-=head1 NAME
+=head1 NAME
DBIx::Class::Manual::Cookbook - Miscellaneous recipes
-=head1 RECIPES
+=head1 SEARCHING
-=head2 Searching
-
-=head3 Paged results
+=head2 Paged results
When you expect a large number of results, you can ask L<DBIx::Class> for a
-paged resultset, which will fetch only a small number of records at a time:
+paged resultset, which will fetch only a defined number of records at a time:
my $rs = $schema->resultset('Artist')->search(
undef,
return $rs->all(); # all records for page 1
-The C<page> attribute does not have to be specified in your search:
-
- my $rs = $schema->resultset('Artist')->search(
- undef,
- {
- rows => 10,
- }
- );
-
- return $rs->page(1); # DBIx::Class::ResultSet containing first 10 records
+ return $rs->page(2); # records for page 2
-In either of the above cases, you can return a L<Data::Page> object for the
-resultset (suitable for use in e.g. a template) using the C<pager> method:
+You can get a L<Data::Page> object for the resultset (suitable for use
+in e.g. a template) using the C<pager> method:
return $rs->pager();
-=head3 Complex WHERE clauses
+=head2 Complex WHERE clauses
Sometimes you need to formulate a query using specific operators:
This results in something like the following C<WHERE> clause:
- WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%'
+ WHERE artist LIKE ? AND title LIKE ?
+
+And the following bind values for the placeholders: C<'%Lamb%'>, C<'%Fear of
+Fours%'>.
Other queries might require slightly more complex logic:
For more information on generating complex queries, see
L<SQL::Abstract/WHERE CLAUSES>.
-=head3 Using specific columns
+=head2 Retrieve one and only one row from a resultset
+
+Sometimes you need only the first "top" row of a resultset. While this
+can be easily done with L<< $rs->first|DBIx::Class::ResultSet/first
+>>, it is suboptimal, as a full blown cursor for the resultset will be
+created and then immediately destroyed after fetching the first row
+object. L<< $rs->single|DBIx::Class::ResultSet/single >> is designed
+specifically for this case - it will grab the first returned result
+without even instantiating a cursor.
+
+Before replacing all your calls to C<first()> with C<single()> please observe the
+following CAVEATS:
+
+=over
+
+=item *
+
+While single() takes a search condition just like search() does, it does
+_not_ accept search attributes. However one can always chain a single() to
+a search():
+
+ my $top_cd = $cd_rs->search({}, { order_by => 'rating' })->single;
+
+
+=item *
+
+Since single() is the engine behind find(), it is designed to fetch a
+single row per database query. Thus a warning will be issued when the
+underlying SELECT returns more than one row. Sometimes however this usage
+is valid: i.e. we have an arbitrary number of cd's but only one of them is
+at the top of the charts at any given time. If you know what you are doing,
+you can silence the warning by explicitly limiting the resultset size:
+
+ my $top_cd = $cd_rs->search ({}, { order_by => 'rating', rows => 1 })->single;
+
+=back
+
+=head2 Arbitrary SQL through a custom ResultSource
+
+Sometimes you have to run arbitrary SQL because your query is too complex
+(e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
+be optimized for your database in a special way, but you still want to
+get the results as a L<DBIx::Class::ResultSet>.
+
+This is accomplished by defining a
+L<ResultSource::View|DBIx::Class::ResultSource::View> for your query,
+almost like you would define a regular ResultSource.
+
+ package My::Schema::Result::UserFriendsComplex;
+ use strict;
+ use warnings;
+ use base qw/DBIx::Class::Core/;
+
+ __PACKAGE__->table_class('DBIx::Class::ResultSource::View');
+
+ # ->table, ->add_columns, etc.
+
+ # do not attempt to deploy() this view
+ __PACKAGE__->result_source_instance->is_virtual(1);
+
+ __PACKAGE__->result_source_instance->view_definition(q[
+ SELECT u.* FROM user u
+ INNER JOIN user_friends f ON u.id = f.user_id
+ WHERE f.friend_user_id = ?
+ UNION
+ SELECT u.* FROM user u
+ INNER JOIN user_friends f ON u.id = f.friend_user_id
+ WHERE f.user_id = ?
+ ]);
+
+Next, you can execute your complex query using bind parameters like this:
+
+ my $friends = $schema->resultset( 'UserFriendsComplex' )->search( {},
+ {
+ bind => [ 12345, 12345 ]
+ }
+ );
+
+... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
+that you cannot modify the rows it contains, e.g. cannot call L</update>,
+L</delete>, ... on it).
+
+Note that you cannot have bind parameters unless is_virtual is set to true.
+
+=over
+
+=item * NOTE
+
+If you're using the old deprecated C<< $rsrc_instance->name(\'( SELECT ...') >>
+method for custom SQL execution, you are highly encouraged to update your code
+to use a virtual view as above. If you do not want to change your code, and just
+want to suppress the deprecation warning when you call
+L<DBIx::Class::Schema/deploy>, add this line to your source definition, so that
+C<deploy> will exclude this "table":
+
+ sub sqlt_deploy_hook { $_[1]->schema->drop_table ($_[1]) }
+
+=back
+
+=head2 Using specific columns
When you only want specific columns from a table, you can use
C<columns> to specify which ones you need. This is useful to avoid
This is a shortcut for C<select> and C<as>, see below. C<columns>
cannot be used together with C<select> and C<as>.
-=head3 Using database functions or stored procedures
+=head2 Using database functions or stored procedures
The combination of C<select> and C<as> can be used to return the result of a
database function or stored procedure as a column value. You use C<select> to
# SELECT name name, LENGTH( name )
# FROM artist
-Note that the C< as > attribute has absolutely nothing to with the sql
-syntax C< SELECT foo AS bar > (see the documentation in
-L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
-column in your base class (i.e. it was added with C<add_columns>), you
-just access it as normal. Our C<Artist> class has a C<name> column, so
-we just use the C<name> accessor:
+Note that the C<as> attribute B<has absolutely nothing to do> with the SQL
+syntax C< SELECT foo AS bar > (see the documentation in
+L<DBIx::Class::ResultSet/ATTRIBUTES>). You can control the C<AS> part of the
+generated SQL via the C<-as> field attribute as follows:
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ join => 'cds',
+ distinct => 1,
+ '+select' => [ { count => 'cds.cdid', -as => 'amount_of_cds' } ],
+ '+as' => [qw/num_cds/],
+ order_by => { -desc => 'amount_of_cds' },
+ }
+ );
+
+ # Equivalent SQL
+ # SELECT me.artistid, me.name, me.rank, me.charfield, COUNT( cds.cdid ) AS amount_of_cds
+ # FROM artist me LEFT JOIN cd cds ON cds.artist = me.artistid
+ # GROUP BY me.artistid, me.name, me.rank, me.charfield
+ # ORDER BY amount_of_cds DESC
+
+
+If your alias exists as a column in your base class (i.e. it was added with
+L<add_columns|DBIx::Class::ResultSource/add_columns>), you just access it as
+normal. Our C<Artist> class has a C<name> column, so we just use the C<name>
+accessor:
my $artist = $rs->first();
my $name = $artist->name();
# Define accessor manually:
sub name_length { shift->get_column('name_length'); }
-
+
# Or use DBIx::Class::AccessorGroup:
__PACKAGE__->mk_group_accessors('column' => 'name_length');
-=head3 SELECT DISTINCT with multiple columns
+See also L</Using SQL functions on the left hand side of a comparison>.
+
+=head2 SELECT DISTINCT with multiple columns
- my $rs = $schema->resultset('Foo')->search(
+ my $rs = $schema->resultset('Artist')->search(
{},
{
- select => [
- { distinct => [ $source->columns ] }
- ],
- as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
+ columns => [ qw/artist_id name rank/ ],
+ distinct => 1
+ }
+ );
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ columns => [ qw/artist_id name rank/ ],
+ group_by => [ qw/artist_id name rank/ ],
}
);
- my $count = $rs->next->get_column('count');
+ # Equivalent SQL:
+ # SELECT me.artist_id, me.name, me.rank
+ # FROM artist me
+ # GROUP BY artist_id, name, rank
-=head3 SELECT COUNT(DISTINCT colname)
+=head2 SELECT COUNT(DISTINCT colname)
- my $rs = $schema->resultset('Foo')->search(
+ my $rs = $schema->resultset('Artist')->search(
{},
{
- select => [
- { count => { distinct => 'colname' } }
- ],
- as => [ 'count' ]
+ columns => [ qw/name/ ],
+ distinct => 1
+ }
+ );
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ columns => [ qw/name/ ],
+ group_by => [ qw/name/ ],
}
);
-=head3 Grouping results
+ my $count = $rs->count;
+
+ # Equivalent SQL:
+ # SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) count_subq:
+
+=head2 Grouping results
L<DBIx::Class> supports C<GROUP BY> as follows:
{},
{
join => [qw/ cds /],
- select => [ 'name', { count => 'cds.cdid' } ],
+ select => [ 'name', { count => 'cds.id' } ],
as => [qw/ name cd_count /],
group_by => [qw/ name /]
}
);
# Equivalent SQL:
- # SELECT name, COUNT( cds.cdid ) FROM artist me
- # LEFT JOIN cd cds ON ( cds.artist = me.artistid )
+ # SELECT name, COUNT( cd.id ) FROM artist
+ # LEFT JOIN cd ON artist.id = cd.artist
# GROUP BY name
Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
are in any way unsure about the use of the attributes above (C< join
>, C< select >, C< as > and C< group_by >).
-=head3 Predefined searches
+=head2 Subqueries
+
+You can write subqueries relatively easily in DBIC.
+
+ my $inside_rs = $schema->resultset('Artist')->search({
+ name => [ 'Billy Joel', 'Brittany Spears' ],
+ });
+
+ my $rs = $schema->resultset('CD')->search({
+ artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
+ });
+
+The usual operators ( =, !=, IN, NOT IN, etc.) are supported.
+
+B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
+The following will B<not> work:
+
+ my $rs = $schema->resultset('CD')->search({
+ artist_id => $inside_rs->get_column('id')->as_query, # does NOT work
+ });
+
+=head3 Support
+
+Subqueries are supported in the where clause (first hashref), and in the
+from, select, and +select attributes.
+
+=head3 Correlated subqueries
+
+ my $cdrs = $schema->resultset('CD');
+ my $rs = $cdrs->search({
+ year => {
+ '=' => $cdrs->search(
+ { artist_id => { '=' => \'me.artist_id' } },
+ { alias => 'inner' }
+ )->get_column('year')->max_rs->as_query,
+ },
+ });
+
+That creates the following SQL:
+
+ SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
+ FROM cd me
+ WHERE year = (
+ SELECT MAX(inner.year)
+ FROM cd inner
+ WHERE artist_id = me.artist_id
+ )
+
+=head2 Predefined searches
You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
-and define often used searches as methods:
+and defining often used searches as methods:
package My::DBIC::ResultSet::CD;
use strict;
1;
-To use your resultset, first tell DBIx::Class to create an instance of it
-for you, in your My::DBIC::Schema::CD class:
+If you're using L<DBIx::Class::Schema/load_namespaces>, simply place the file
+into the C<ResultSet> directory next to your C<Result> directory, and it will
+be automatically loaded.
+
+If however you are still using L<DBIx::Class::Schema/load_classes>, first tell
+DBIx::Class to create an instance of the ResultSet class for you, in your
+My::DBIC::Schema::CD class:
+
+ # class definition as normal
+ use base 'DBIx::Class::Core';
+ __PACKAGE__->table('cd');
+ # tell DBIC to use the custom ResultSet class
__PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
+Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
+
Then call your new method in your code:
my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
+=head2 Using SQL functions on the left hand side of a comparison
-=head3 Predefined searches without writing a ResultSet class
+Using SQL functions on the left hand side of a comparison is generally not a
+good idea since it requires a scan of the entire table. (Unless your RDBMS
+supports indexes on expressions - including return values of functions - and
+you create an index on the return value of the function in question.) However,
+it can be accomplished with C<DBIx::Class> when necessary.
-Alternatively you can automatically generate a DBIx::Class::ResultSet
-class by using the ResultSetManager component and tagging your method
-as ResultSet:
+If you do not have quoting on, simply include the function in your search
+specification as you would any column:
- __PACKAGE__->load_components(qw/ ResultSetManager Core /);
+ $rs->search({ 'YEAR(date_of_birth)' => 1979 });
- sub search_cds_ordered : ResultSet {
- my ($self) = @_;
- return $self->search(
- {},
- { order_by => 'name DESC' },
- );
- }
+With quoting on, or for a more portable solution, use literal SQL values with
+placeholders:
-Then call your method in the same way from your code:
+ $rs->search(\[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ]);
- my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
+ # Equivalent SQL:
+ # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?
+
+ $rs->search({
+ name => 'Bob',
+ -nest => \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ],
+ });
+
+ # Equivalent SQL:
+ # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?
+
+Note: the C<plain_value> string in the C<< [ plain_value => 1979 ] >> part
+should be either the same as the name of the column (do this if the type of the
+return value of the function is the same as the type of the column) or
+otherwise it's essentially a dummy string currently (use C<plain_value> as a
+habit). It is used by L<DBIx::Class> to handle special column types.
+
+See also L<SQL::Abstract/Literal SQL with placeholders and bind values
+(subqueries)>.
+
+=head1 JOINS AND PREFETCHING
=head2 Using joins and prefetch
You can use the C<join> attribute to allow searching on, or sorting your
-results by, one or more columns in a related table. To return all CDs matching
-a particular artist name:
+results by, one or more columns in a related table.
+
+This requires that you have defined the L<DBIx::Class::Relationship>. For example :
+
+ My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
+
+To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
my $rs = $schema->resultset('CD')->search(
{
- 'artist.name' => 'Bob Marley'
+ 'artists.name' => 'Bob Marley'
},
{
- join => [qw/artist/], # join the artist table
+ join => 'artists', # join the artist table
}
);
# JOIN artist ON cd.artist = artist.id
# WHERE artist.name = 'Bob Marley'
+In that example both the join, and the condition use the relationship name rather than the table name
+(see L<DBIx::Class::Manual::Joining> for more details on aliasing ).
+
If required, you can now sort on any column in the related tables by including
-it in your C<order_by> attribute:
+it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
my $rs = $schema->resultset('CD')->search(
{
- 'artist.name' => 'Bob Marley'
+ 'artists.name' => 'Bob Marley'
},
{
- join => [qw/ artist /],
- order_by => [qw/ artist.name /]
+ join => 'artists',
+ order_by => [qw/ artists.name /]
}
- };
+ );
# Equivalent SQL:
# SELECT cd.* FROM cd
my $rs = $schema->resultset('CD')->search(
{
- 'artist.name' => 'Bob Marley'
+ 'artists.name' => 'Bob Marley'
},
{
- join => [qw/ artist /],
- order_by => [qw/ artist.name /],
- prefetch => [qw/ artist /] # return artist data too!
+ join => 'artists',
+ order_by => [qw/ artists.name /],
+ prefetch => 'artists' # return artist data too!
}
);
so no additional SQL statements are executed. You now have a much more
efficient query.
-Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
-C<has_many> relationships.
-
Also note that C<prefetch> should only be used when you know you will
definitely use data from a related table. Pre-fetching related tables when you
only need columns from the main table will make performance worse!
-=head3 Multi-step joins
+=head2 Multiple joins
+
+In the examples above, the C<join> attribute was a scalar. If you
+pass an array reference instead, you can join to multiple tables. In
+this example, we want to limit the search further, using
+C<LinerNotes>:
+
+ # Relationships defined elsewhere:
+ # CD->belongs_to('artist' => 'Artist');
+ # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
+ my $rs = $schema->resultset('CD')->search(
+ {
+ 'artist.name' => 'Bob Marley'
+ 'liner_notes.notes' => { 'like', '%some text%' },
+ },
+ {
+ join => [qw/ artist liner_notes /],
+ order_by => [qw/ artist.name /],
+ }
+ );
+
+ # Equivalent SQL:
+ # SELECT cd.*, artist.*, liner_notes.* FROM cd
+ # JOIN artist ON cd.artist = artist.id
+ # JOIN liner_notes ON cd.id = liner_notes.cd
+ # WHERE artist.name = 'Bob Marley'
+ # ORDER BY artist.name
+
+=head2 Multi-step joins
Sometimes you want to join more than one relationship deep. In this example,
we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
# Equivalent SQL:
# SELECT artist.* FROM artist
- # JOIN ( cd ON artist.id = cd.artist )
- # JOIN ( liner_notes ON cd.id = liner_notes.cd )
+ # LEFT JOIN cd ON artist.id = cd.artist
+ # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
# WHERE liner_notes.notes LIKE '%some text%'
Joins can be nested to an arbitrary level. So if we decide later that we
# Equivalent SQL:
# SELECT artist.* FROM artist
- # JOIN ( cd ON artist.id = cd.artist )
- # JOIN ( liner_notes ON cd.id = liner_notes.cd )
- # JOIN ( author ON author.id = liner_notes.author )
+ # LEFT JOIN cd ON artist.id = cd.artist
+ # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
+ # LEFT JOIN author ON author.id = liner_notes.author
# WHERE liner_notes.notes LIKE '%some text%'
# AND author.name = 'A. Writer'
+=head2 Multi-step and multiple joins
+
+With various combinations of array and hash references, you can join
+tables in any combination you desire. For example, to join Artist to
+CD and Concert, and join CD to LinerNotes:
+
+ # Relationships defined elsewhere:
+ # Artist->has_many('concerts' => 'Concert', 'artist');
+
+ my $rs = $schema->resultset('Artist')->search(
+ { },
+ {
+ join => [
+ {
+ cds => 'liner_notes'
+ },
+ 'concerts'
+ ],
+ }
+ );
+
+ # Equivalent SQL:
+ # SELECT artist.* FROM artist
+ # LEFT JOIN cd ON artist.id = cd.artist
+ # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
+ # LEFT JOIN concert ON artist.id = concert.artist
+
=head2 Multi-step prefetch
-From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
+C<prefetch> can be nested more than one relationship
deep using the same syntax as a multi-step join:
my $rs = $schema->resultset('Tag')->search(
# Equivalent SQL:
# SELECT tag.*, cd.*, artist.* FROM tag
- # JOIN cd ON tag.cd = cd.cdid
- # JOIN artist ON cd.artist = artist.artistid
+ # JOIN cd ON tag.cd = cd.id
+ # JOIN artist ON cd.artist = artist.id
Now accessing our C<cd> and C<artist> relationships does not need additional
SQL statements:
my $tag = $rs->first;
print $tag->cd->artist->name;
-=head2 Columns of data
+=head1 ROW-LEVEL OPERATIONS
-If you want to find the sum of a particular column there are several
-ways, the obvious one is to use search:
+=head2 Retrieving a row object's Schema
- my $rs = $schema->resultset('Items')->search(
- {},
- {
- select => [ { sum => 'Cost' } ],
- as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
- }
- );
- my $tc = $rs->first->get_column('total_cost');
+It is possible to get a Schema object from a row object like so:
-Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
-returned when you ask the C<ResultSet> for a column using
-C<get_column>:
+ my $schema = $cd->result_source->schema;
+ # use the schema as normal:
+ my $artist_rs = $schema->resultset('Artist');
- my $cost = $schema->resultset('Items')->get_column('Cost');
- my $tc = $cost->sum;
+This can be useful when you don't want to pass around a Schema object to every
+method.
-With this you can also do:
+=head2 Getting the value of the primary key for the last database insert
- my $minvalue = $cost->min;
- my $maxvalue = $cost->max;
+AKA getting last_insert_id
-Or just iterate through the values of this column only:
+Thanks to the core component PK::Auto, this is straightforward:
- while ( my $c = $cost->next ) {
- print $c;
- }
+ my $foo = $rs->create(\%blah);
+ # do more stuff
+ my $id = $foo->id; # foo->my_primary_key_field will also work.
- foreach my $c ($cost->all) {
- print $c;
- }
+If you are not using autoincrementing primary keys, this will probably
+not work, but then you already know the value of the last primary key anyway.
-C<ResultSetColumn> only has a limited number of built-in functions, if
-you need one that it doesn't have, then you can use the C<func> method
-instead:
+=head2 Stringification
- my $avg = $cost->func('AVERAGE');
+Employ the standard stringification technique by using the L<overload>
+module.
-This will cause the following SQL statement to be run:
+To make an object stringify itself as a single column, use something
+like this (replace C<name> with the column/method of your choice):
- SELECT AVERAGE(Cost) FROM Items me
+ use overload '""' => sub { shift->name}, fallback => 1;
-Which will of course only work if your database supports this function.
-See L<DBIx::Class::ResultSetColumn> for more documentation.
+For more complex stringification, you can use an anonymous subroutine:
-=head2 Using relationships
+ use overload '""' => sub { $_[0]->name . ", " .
+ $_[0]->address }, fallback => 1;
-=head3 Create a new row in a related table
+=head3 Stringification Example
- my $book->create_related('author', { name => 'Fred'});
+Suppose we have two tables: C<Product> and C<Category>. The table
+specifications are:
-=head3 Search in a related table
+ Product(id, Description, category)
+ Category(id, Description)
-Only searches for books named 'Titanic' by the author in $author.
+C<category> is a foreign key into the Category table.
- my $author->search_related('books', { name => 'Titanic' });
+If you have a Product object C<$obj> and write something like
-=head3 Delete data in a related table
+ print $obj->category
-Deletes only the book named Titanic by the author in $author.
+things will not work as expected.
- my $author->delete_related('books', { name => 'Titanic' });
+To obtain, for example, the category description, you should add this
+method to the class defining the Category table:
-=head3 Ordering a relationship result set
+ use overload "" => sub {
+ my $self = shift;
-If you always want a relation to be ordered, you can specify this when you
-create the relationship.
+ return $self->Description;
+ }, fallback => 1;
-To order C<< $book->pages >> by descending page_number.
+=head2 Want to know if find_or_create found or created a row?
- Book->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
+Just use C<find_or_new> instead, then check C<in_storage>:
+ my $obj = $rs->find_or_new({ blah => 'blarg' });
+ unless ($obj->in_storage) {
+ $obj->insert;
+ # do whatever else you wanted if it was a new row
+ }
+=head2 Static sub-classing DBIx::Class result classes
-=head2 Transactions
+AKA adding additional relationships/methods/etc. to a model for a
+specific usage of the (shared) model.
-As of version 0.04001, there is improved transaction support in
-L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
-example of the recommended way to use it:
+B<Schema definition>
- my $genus = $schema->resultset('Genus')->find(12);
+ package My::App::Schema;
- my $coderef2 = sub {
- $genus->extinct(1);
- $genus->update;
- };
+ use base 'DBIx::Class::Schema';
- my $coderef1 = sub {
- $genus->add_to_species({ name => 'troglodyte' });
- $genus->wings(2);
- $genus->update;
- $schema->txn_do($coderef2); # Can have a nested transaction
- return $genus->species;
- };
+ # load subclassed classes from My::App::Schema::Result/ResultSet
+ __PACKAGE__->load_namespaces;
- my $rs;
- eval {
- $rs = $schema->txn_do($coderef1);
- };
+ # load classes from shared model
+ load_classes({
+ 'My::Shared::Model::Result' => [qw/
+ Foo
+ Bar
+ /]});
- if ($@) { # Transaction failed
- die "the sky is falling!" #
- if ($@ =~ /Rollback failed/); # Rollback failed
+ 1;
- deal_with_failed_transaction();
- }
+B<Result-Subclass definition>
-Nested transactions will work as expected. That is, only the outermost
-transaction will actually issue a commit to the $dbh, and a rollback
-at any level of any transaction will cause the entire nested
-transaction to fail. Support for savepoints and for true nested
-transactions (for databases that support them) will hopefully be added
-in the future.
+ package My::App::Schema::Result::Baz;
+
+ use strict;
+ use warnings;
+ use base 'My::Shared::Model::Result::Baz';
+
+ # WARNING: Make sure you call table() again in your subclass,
+ # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
+ # and the class name is not correctly registered as a source
+ __PACKAGE__->table('baz');
+
+ sub additional_method {
+ return "I'm an additional method only needed by this app";
+ }
+
+ 1;
+
+=head2 Dynamic Sub-classing DBIx::Class proxy classes
+
+AKA multi-class object inflation from one table
+
+L<DBIx::Class> classes are proxy classes, therefore some different
+techniques need to be employed for more than basic subclassing. In
+this example we have a single user table that carries a boolean bit
+for admin. We would like like to give the admin users
+objects (L<DBIx::Class::Row>) the same methods as a regular user but
+also special admin only methods. It doesn't make sense to create two
+separate proxy-class files for this. We would be copying all the user
+methods into the Admin class. There is a cleaner way to accomplish
+this.
+
+Overriding the C<inflate_result> method within the User proxy-class
+gives us the effect we want. This method is called by
+L<DBIx::Class::ResultSet> when inflating a result from storage. So we
+grab the object being returned, inspect the values we are looking for,
+bless it if it's an admin object, and then return it. See the example
+below:
+
+B<Schema Definition>
+
+ package My::Schema;
+
+ use base qw/DBIx::Class::Schema/;
+
+ __PACKAGE__->load_namespaces;
+
+ 1;
+
+
+B<Proxy-Class definitions>
+
+ package My::Schema::Result::User;
+
+ use strict;
+ use warnings;
+ use base qw/DBIx::Class::Core/;
+
+ ### Define what our admin class is, for ensure_class_loaded()
+ my $admin_class = __PACKAGE__ . '::Admin';
+
+ __PACKAGE__->table('users');
+
+ __PACKAGE__->add_columns(qw/user_id email password
+ firstname lastname active
+ admin/);
+
+ __PACKAGE__->set_primary_key('user_id');
+
+ sub inflate_result {
+ my $self = shift;
+ my $ret = $self->next::method(@_);
+ if( $ret->admin ) {### If this is an admin, rebless for extra functions
+ $self->ensure_class_loaded( $admin_class );
+ bless $ret, $admin_class;
+ }
+ return $ret;
+ }
+
+ sub hello {
+ print "I am a regular user.\n";
+ return ;
+ }
+
+ 1;
+
+
+ package My::Schema::Result::User::Admin;
+
+ use strict;
+ use warnings;
+ use base qw/My::Schema::Result::User/;
+
+ # This line is important
+ __PACKAGE__->table('users');
+
+ sub hello
+ {
+ print "I am an admin.\n";
+ return;
+ }
+
+ sub do_admin_stuff
+ {
+ print "I am doing admin stuff\n";
+ return ;
+ }
+
+ 1;
+
+B<Test File> test.pl
+
+ use warnings;
+ use strict;
+ use My::Schema;
+
+ my $user_data = { email => 'someguy@place.com',
+ password => 'pass1',
+ admin => 0 };
+
+ my $admin_data = { email => 'someadmin@adminplace.com',
+ password => 'pass2',
+ admin => 1 };
+
+ my $schema = My::Schema->connection('dbi:Pg:dbname=test');
+
+ $schema->resultset('User')->create( $user_data );
+ $schema->resultset('User')->create( $admin_data );
+
+ ### Now we search for them
+ my $user = $schema->resultset('User')->single( $user_data );
+ my $admin = $schema->resultset('User')->single( $admin_data );
+
+ print ref $user, "\n";
+ print ref $admin, "\n";
+
+ print $user->password , "\n"; # pass1
+ print $admin->password , "\n";# pass2; inherited from User
+ print $user->hello , "\n";# I am a regular user.
+ print $admin->hello, "\n";# I am an admin.
+
+ ### The statement below will NOT print
+ print "I can do admin stuff\n" if $user->can('do_admin_stuff');
+ ### The statement below will print
+ print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
+
+Alternatively you can use L<DBIx::Class::DynamicSubclass> that implements
+exactly the above functionality.
+
+=head2 Skip row object creation for faster results
+
+DBIx::Class is not built for speed, it's built for convenience and
+ease of use, but sometimes you just need to get the data, and skip the
+fancy objects.
+
+To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
+
+ my $rs = $schema->resultset('CD');
+
+ $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
+
+ my $hash_ref = $rs->find(1);
+
+Wasn't that easy?
+
+Beware, changing the Result class using
+L<DBIx::Class::ResultSet/result_class> will replace any existing class
+completely including any special components loaded using
+load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
+
+=head2 Get raw data for blindingly fast results
+
+If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
+above is not fast enough for you, you can use a DBIx::Class to return values
+exactly as they come out of the database with none of the convenience methods
+wrapped round them.
+
+This is used like so:
+
+ my $cursor = $rs->cursor
+ while (my @vals = $cursor->next) {
+ # use $val[0..n] here
+ }
+
+You will need to map the array offsets to particular columns (you can
+use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
+
+=head1 RESULTSET OPERATIONS
+
+=head2 Getting Schema from a ResultSet
+
+To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
+
+ $rs->result_source->schema
+
+=head2 Getting Columns Of Data
+
+AKA Aggregating Data
+
+If you want to find the sum of a particular column there are several
+ways, the obvious one is to use search:
+
+ my $rs = $schema->resultset('Items')->search(
+ {},
+ {
+ select => [ { sum => 'Cost' } ],
+ as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
+ }
+ );
+ my $tc = $rs->first->get_column('total_cost');
+
+Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
+returned when you ask the C<ResultSet> for a column using
+C<get_column>:
+
+ my $cost = $schema->resultset('Items')->get_column('Cost');
+ my $tc = $cost->sum;
+
+With this you can also do:
+
+ my $minvalue = $cost->min;
+ my $maxvalue = $cost->max;
+
+Or just iterate through the values of this column only:
+
+ while ( my $c = $cost->next ) {
+ print $c;
+ }
+
+ foreach my $c ($cost->all) {
+ print $c;
+ }
+
+C<ResultSetColumn> only has a limited number of built-in functions. If
+you need one that it doesn't have, then you can use the C<func> method
+instead:
+
+ my $avg = $cost->func('AVERAGE');
+
+This will cause the following SQL statement to be run:
+
+ SELECT AVERAGE(Cost) FROM Items me
+
+Which will of course only work if your database supports this function.
+See L<DBIx::Class::ResultSetColumn> for more documentation.
+
+=head2 Creating a result set from a set of rows
+
+Sometimes you have a (set of) row objects that you want to put into a
+resultset without the need to hit the DB again. You can do that by using the
+L<set_cache|DBIx::Class::Resultset/set_cache> method:
+
+ my @uploadable_groups;
+ while (my $group = $groups->next) {
+ if ($group->can_upload($self)) {
+ push @uploadable_groups, $group;
+ }
+ }
+ my $new_rs = $self->result_source->resultset;
+ $new_rs->set_cache(\@uploadable_groups);
+ return $new_rs;
+
+
+=head1 USING RELATIONSHIPS
+
+=head2 Create a new row in a related table
+
+ my $author = $book->create_related('author', { name => 'Fred'});
+
+=head2 Search in a related table
+
+Only searches for books named 'Titanic' by the author in $author.
+
+ my $books_rs = $author->search_related('books', { name => 'Titanic' });
+
+=head2 Delete data in a related table
+
+Deletes only the book named Titanic by the author in $author.
+
+ $author->delete_related('books', { name => 'Titanic' });
+
+=head2 Ordering a relationship result set
+
+If you always want a relation to be ordered, you can specify this when you
+create the relationship.
+
+To order C<< $book->pages >> by descending page_number, create the relation
+as follows:
+
+ __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );
+
+=head2 Filtering a relationship result set
+
+If you want to get a filtered result set, you can just add add to $attr as follows:
+
+ __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
=head2 Many-to-many relationships
This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
- package My::DB;
- # ... set up connection ...
-
package My::User;
- use base 'My::DB';
+ use base 'DBIx::Class::Core';
__PACKAGE__->table('user');
__PACKAGE__->add_columns(qw/id name/);
__PACKAGE__->set_primary_key('id');
__PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
package My::UserAddress;
- use base 'My::DB';
+ use base 'DBIx::Class::Core';
__PACKAGE__->table('user_address');
__PACKAGE__->add_columns(qw/user address/);
__PACKAGE__->set_primary_key(qw/user address/);
__PACKAGE__->belongs_to('address' => 'My::Address');
package My::Address;
- use base 'My::DB';
+ use base 'DBIx::Class::Core';
__PACKAGE__->table('address');
__PACKAGE__->add_columns(qw/id street town area_code country/);
__PACKAGE__->set_primary_key('id');
$rs = $user->addresses(); # get all addresses for a user
$rs = $address->users(); # get all users for an address
-=head2 Setting default values for a row
+ my $address = $user->add_to_addresses( # returns a My::Address instance,
+ # NOT a My::UserAddress instance!
+ {
+ country => 'United Kingdom',
+ area_code => 'XYZ',
+ town => 'London',
+ street => 'Sesame',
+ }
+ );
-It's as simple as overriding the C<new> method. Note the use of
-C<next::method>.
+=head2 Relationships across DB schemas
- sub new {
- my ( $class, $attrs ) = @_;
+Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
+is easy as long as the schemas themselves are all accessible via the same DBI
+connection. In most cases, this means that they are on the same database host
+as each other and your connecting database user has the proper permissions to them.
- $attrs->{foo} = 'bar' unless defined $attrs->{foo};
+To accomplish this one only needs to specify the DB schema name in the table
+declaration, like so...
+
+ package MyDatabase::Main::Artist;
+ use base qw/DBIx::Class::Core/;
+
+ __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
+
+ __PACKAGE__->add_columns(qw/ artist_id name /);
+ __PACKAGE__->set_primary_key('artist_id');
+ __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
- $class->next::method($attrs);
+ 1;
+
+Whatever string you specify there will be used to build the "FROM" clause in SQL
+queries.
+
+The big drawback to this is you now have DB schema names hardcoded in your
+class files. This becomes especially troublesome if you have multiple instances
+of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
+the DB schemas are named based on the environment (e.g. database1_dev).
+
+However, one can dynamically "map" to the proper DB schema by overriding the
+L<connection|DBIx::Class::Schama/connection> method in your Schema class and
+building a renaming facility, like so:
+
+ package MyDatabase::Schema;
+ use Moose;
+
+ extends 'DBIx::Class::Schema';
+
+ around connection => sub {
+ my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
+
+ my $postfix = delete $attr->{schema_name_postfix};
+
+ $inner->(@_);
+
+ if ( $postfix ) {
+ $self->append_db_name($postfix);
+ }
+ };
+
+ sub append_db_name {
+ my ( $self, $postfix ) = @_;
+
+ my @sources_with_db
+ = grep
+ { $_->name =~ /^\w+\./mx }
+ map
+ { $self->source($_) }
+ $self->sources;
+
+ foreach my $source (@sources_with_db) {
+ my $name = $source->name;
+ $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
+
+ $source->name($name);
+ }
}
-For more information about C<next::method>, look in the L<Class::C3>
-documentation. See also L<DBIx::Class::Manual::Component> for more
-ways to write your own base classes to do this.
+ 1;
-People looking for ways to do "triggers" with DBIx::Class are probably
-just looking for this.
+By overridding the L<connection|DBIx::Class::Schama/connection>
+method and extracting a custom option from the provided \%attr hashref one can
+then simply iterate over all the Schema's ResultSources, renaming them as
+needed.
-=head2 Stringification
+To use this facility, simply add or modify the \%attr hashref that is passed to
+L<connection|DBIx::Class::Schama/connect>, as follows:
-Employ the standard stringification technique by using the C<overload>
-module.
+ my $schema
+ = MyDatabase::Schema->connect(
+ $dsn,
+ $user,
+ $pass,
+ {
+ schema_name_postfix => '_dev'
+ # ... Other options as desired ...
+ })
-To make an object stringify itself as a single column, use something
-like this (replace C<foo> with the column/method of your choice):
+Obviously, one could accomplish even more advanced mapping via a hash map or a
+callback routine.
- use overload '""' => sub { shift->name}, fallback => 1;
+=head1 TRANSACTIONS
-For more complex stringification, you can use an anonymous subroutine:
+As of version 0.04001, there is improved transaction support in
+L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
+example of the recommended way to use it:
- use overload '""' => sub { $_[0]->name . ", " .
- $_[0]->address }, fallback => 1;
+ my $genus = $schema->resultset('Genus')->find(12);
-=head3 Stringification Example
+ my $coderef2 = sub {
+ $genus->extinct(1);
+ $genus->update;
+ };
-Suppose we have two tables: C<Product> and C<Category>. The table
-specifications are:
+ my $coderef1 = sub {
+ $genus->add_to_species({ name => 'troglodyte' });
+ $genus->wings(2);
+ $genus->update;
+ $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
+ return $genus->species;
+ };
- Product(id, Description, category)
- Category(id, Description)
+ my $rs;
+ eval {
+ $rs = $schema->txn_do($coderef1);
+ };
-C<category> is a foreign key into the Category table.
+ if ($@) { # Transaction failed
+ die "the sky is falling!" #
+ if ($@ =~ /Rollback failed/); # Rollback failed
-If you have a Product object C<$obj> and write something like
+ deal_with_failed_transaction();
+ }
+
+Nested transactions will work as expected. That is, only the outermost
+transaction will actually issue a commit to the $dbh, and a rollback
+at any level of any transaction will cause the entire nested
+transaction to fail.
+
+=head2 Nested transactions and auto-savepoints
+
+If savepoints are supported by your RDBMS, it is possible to achieve true
+nested transactions with minimal effort. To enable auto-savepoints via nested
+transactions, supply the C<< auto_savepoint = 1 >> connection attribute.
+
+Here is an example of true nested transactions. In the example, we start a big
+task which will create several rows. Generation of data for each row is a
+fragile operation and might fail. If we fail creating something, depending on
+the type of failure, we want to abort the whole task, or only skip the failed
+row.
+
+ my $schema = MySchema->connect("dbi:Pg:dbname=my_db");
+
+ # Start a transaction. Every database change from here on will only be
+ # committed into the database if the eval block succeeds.
+ eval {
+ $schema->txn_do(sub {
+ # SQL: BEGIN WORK;
+
+ my $job = $schema->resultset('Job')->create({ name=> 'big job' });
+ # SQL: INSERT INTO job ( name) VALUES ( 'big job' );
+
+ for (1..10) {
+
+ # Start a nested transaction, which in fact sets a savepoint.
+ eval {
+ $schema->txn_do(sub {
+ # SQL: SAVEPOINT savepoint_0;
+
+ my $thing = $schema->resultset('Thing')->create({ job=>$job->id });
+ # SQL: INSERT INTO thing ( job) VALUES ( 1 );
+
+ if (rand > 0.8) {
+ # This will generate an error, thus setting $@
+
+ $thing->update({force_fail=>'foo'});
+ # SQL: UPDATE thing SET force_fail = 'foo'
+ # WHERE ( id = 42 );
+ }
+ });
+ };
+ if ($@) {
+ # SQL: ROLLBACK TO SAVEPOINT savepoint_0;
+
+ # There was an error while creating a $thing. Depending on the error
+ # we want to abort the whole transaction, or only rollback the
+ # changes related to the creation of this $thing
+
+ # Abort the whole job
+ if ($@ =~ /horrible_problem/) {
+ print "something horrible happend, aborting job!";
+ die $@; # rethrow error
+ }
+
+ # Ignore this $thing, report the error, and continue with the
+ # next $thing
+ print "Cannot create thing: $@";
+ }
+ # There was no error, so save all changes since the last
+ # savepoint.
+
+ # SQL: RELEASE SAVEPOINT savepoint_0;
+ }
+ });
+ };
+ if ($@) {
+ # There was an error while handling the $job. Rollback all changes
+ # since the transaction started, including the already committed
+ # ('released') savepoints. There will be neither a new $job nor any
+ # $thing entry in the database.
+
+ # SQL: ROLLBACK;
+
+ print "ERROR: $@\n";
+ }
+ else {
+ # There was no error while handling the $job. Commit all changes.
+ # Only now other connections can see the newly created $job and
+ # @things.
+
+ # SQL: COMMIT;
+
+ print "Ok\n";
+ }
+
+In this example it might be hard to see where the rollbacks, releases and
+commits are happening, but it works just the same as for plain L<<txn_do>>: If
+the C<eval>-block around C<txn_do> fails, a rollback is issued. If the C<eval>
+succeeds, the transaction is committed (or the savepoint released).
+
+While you can get more fine-grained controll using C<svp_begin>, C<svp_release>
+and C<svp_rollback>, it is strongly recommended to use C<txn_do> with coderefs.
+
+=head1 SQL
+
+=head2 Creating Schemas From An Existing Database
+
+L<DBIx::Class::Schema::Loader> will connect to a database and create a
+L<DBIx::Class::Schema> and associated sources by examining the database.
+
+The recommend way of achieving this is to use the
+L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
+
+ perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
+ -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
+
+This will create a tree of files rooted at C<./lib/My/Schema/> containing
+source definitions for all the tables found in the C<foo> database.
+
+=head2 Creating DDL SQL
+
+The following functionality requires you to have L<SQL::Translator>
+(also known as "SQL Fairy") installed.
+
+To create a set of database-specific .sql files for the above schema:
+
+ my $schema = My::Schema->connect($dsn);
+ $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
+ '0.1',
+ './dbscriptdir/'
+ );
+
+By default this will create schema files in the current directory, for
+MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
+
+To create a new database using the schema:
+
+ my $schema = My::Schema->connect($dsn);
+ $schema->deploy({ add_drop_table => 1});
+
+To import created .sql files using the mysql client:
+
+ mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
+
+To create C<ALTER TABLE> conversion scripts to update a database to a
+newer version of your schema at a later point, first set a new
+C<$VERSION> in your Schema file, then:
+
+ my $schema = My::Schema->connect($dsn);
+ $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
+ '0.2',
+ '/dbscriptdir/',
+ '0.1'
+ );
+
+This will produce new database-specific .sql files for the new version
+of the schema, plus scripts to convert from version 0.1 to 0.2. This
+requires that the files for 0.1 as created above are available in the
+given directory to diff against.
+
+=head2 Select from dual
+
+Dummy tables are needed by some databases to allow calling functions
+or expressions that aren't based on table content, for examples of how
+this applies to various database types, see:
+L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
+
+Note: If you're using Oracles dual table don't B<ever> do anything
+other than a select, if you CRUD on your dual table you *will* break
+your database.
+
+Make a table class as you would for any other table
+
+ package MyAppDB::Dual;
+ use strict;
+ use warnings;
+ use base 'DBIx::Class::Core';
+ __PACKAGE__->table("Dual");
+ __PACKAGE__->add_columns(
+ "dummy",
+ { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
+ );
+
+Once you've loaded your table class select from it using C<select>
+and C<as> instead of C<columns>
+
+ my $rs = $schema->resultset('Dual')->search(undef,
+ { select => [ 'sydate' ],
+ as => [ 'now' ]
+ },
+ );
+
+All you have to do now is be careful how you access your resultset, the below
+will not work because there is no column called 'now' in the Dual table class
+
+ while (my $dual = $rs->next) {
+ print $dual->now."\n";
+ }
+ # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
+
+You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
+your Dual class for whatever you wanted to select from dual, but that's just
+silly, instead use C<get_column>
+
+ while (my $dual = $rs->next) {
+ print $dual->get_column('now')."\n";
+ }
+
+Or use C<cursor>
+
+ my $cursor = $rs->cursor;
+ while (my @vals = $cursor->next) {
+ print $vals[0]."\n";
+ }
+
+In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
+L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
+current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
+"sequence.nextval" anymore from dual. To avoid this problem, just tell
+L<SQL::Translator> to not create table dual:
+
+ my $sqlt_args = {
+ add_drop_table => 1,
+ parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
+ };
+ $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
+
+Or use L<DBIx::Class::ResultClass::HashRefInflator>
+
+ $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
+ while ( my $dual = $rs->next ) {
+ print $dual->{now}."\n";
+ }
+
+Here are some example C<select> conditions to illustrate the different syntax
+you could use for doing stuff like
+C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
+
+ # get a sequence value
+ select => [ 'A_SEQ.nextval' ],
+
+ # get create table sql
+ select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
+
+ # get a random num between 0 and 100
+ select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
+
+ # what year is it?
+ select => [ { 'extract' => [ \'year from sysdate' ] } ],
+
+ # do some math
+ select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
+
+ # which day of the week were you born on?
+ select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
- print $obj->category
+ # select 16 rows from dual
+ select => [ "'hello'" ],
+ as => [ 'world' ],
+ group_by => [ 'cube( 1, 2, 3, 4 )' ],
-things will not work as expected.
-To obtain, for example, the category description, you should add this
-method to the class defining the Category table:
- use overload "" => sub {
- my $self = shift;
+=head2 Adding Indexes And Functions To Your SQL
- return $self->Description;
- }, fallback => 1;
+Often you will want indexes on columns on your table to speed up searching. To
+do this, create a method called C<sqlt_deploy_hook> in the relevant source
+class (refer to the advanced
+L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
+to share a hook between multiple sources):
-=head2 Disconnecting cleanly
+ package My::Schema::Result::Artist;
-If you find yourself quitting an app with Control-C a lot during
-development, you might like to put the following signal handler in
-your main database class to make sure it disconnects cleanly:
+ __PACKAGE__->table('artist');
+ __PACKAGE__->add_columns(id => { ... }, name => { ... })
- $SIG{INT} = sub {
- __PACKAGE__->storage->disconnect;
- };
+ sub sqlt_deploy_hook {
+ my ($self, $sqlt_table) = @_;
-=head2 Schema import/export
+ $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
+ }
-This functionality requires you to have L<SQL::Translator> (also known as
-"SQL Fairy") installed.
+ 1;
-To create a DBIx::Class schema from an existing database:
+Sometimes you might want to change the index depending on the type of the
+database for which SQL is being generated:
- sqlt --from DBI
- --to DBIx::Class::File
- --prefix "MySchema" > MySchema.pm
+ my ($db_type = $sqlt_table->schema->translator->producer_type)
+ =~ s/^SQL::Translator::Producer:://;
-To create a MySQL database from an existing L<DBIx::Class> schema, convert the
-schema to MySQL's dialect of SQL:
+You can also add hooks to the schema level to stop certain tables being
+created:
- sqlt --from SQL::Translator::Parser::DBIx::Class
- --to MySQL
- --DBIx::Class "MySchema.pm" > Schema1.sql
-
-And import using the mysql client:
+ package My::Schema;
- mysql -h "host" -D "database" -u "user" -p < Schema1.sql
+ ...
-=head2 Easy migration from class-based to schema-based setup
+ sub sqlt_deploy_hook {
+ my ($self, $sqlt_schema) = @_;
-You want to start using the schema-based approach to L<DBIx::Class>
-(see L<SchemaIntro.pod>), but have an established class-based setup with lots
-of existing classes that you don't want to move by hand. Try this nifty script
-instead:
+ $sqlt_schema->drop_table('table_name');
+ }
- use MyDB;
- use SQL::Translator;
-
- my $schema = MyDB->schema_instance;
-
- my $translator = SQL::Translator->new(
- debug => $debug || 0,
- trace => $trace || 0,
- no_comments => $no_comments || 0,
- show_warnings => $show_warnings || 0,
- add_drop_table => $add_drop_table || 0,
- validate => $validate || 0,
- parser_args => {
- 'DBIx::Schema' => $schema,
- },
- producer_args => {
- 'prefix' => 'My::Schema',
- },
- );
-
- $translator->parser('SQL::Translator::Parser::DBIx::Class');
- $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
-
- my $output = $translator->translate(@args) or die
- "Error: " . $translator->error;
-
- print $output;
+You could also add views, procedures or triggers to the output using
+L<SQL::Translator::Schema/add_view>,
+L<SQL::Translator::Schema/add_procedure> or
+L<SQL::Translator::Schema/add_trigger>.
-You could use L<Module::Find> to search for all subclasses in the MyDB::*
-namespace, which is currently left as an exercise for the reader.
=head2 Schema versioning
=back
-=head3 Create a DBIx::Class schema
+B<Create a DBIx::Class schema>
This can either be done manually, or generated from an existing database as
-described under C<Schema import/export>.
-
-=head3 Save the schema
-
-Use C<sqlt> to transform your schema into an SQL script suitable for your
-customer's database. E.g. for MySQL:
-
- sqlt --from SQL::Translator::Parser::DBIx::Class
- --to MySQL
- --DBIx::Class "MySchema.pm" > Schema1.mysql.sql
+described under L</Creating Schemas From An Existing Database>
-If you need to target databases from multiple vendors, just generate an SQL
-script suitable for each. To support PostgreSQL too:
+B<Save the schema>
- sqlt --from SQL::Translator::DBIx::Class
- --to PostgreSQL
- --DBIx::Class "MySchema.pm" > Schema1.pgsql.sql
+Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
-=head3 Deploy to customers
+B<Deploy to customers>
There are several ways you could deploy your schema. These are probably
beyond the scope of this recipe, but might include:
=back
-=head3 Modify the schema to change functionality
+B<Modify the schema to change functionality>
+
+As your application evolves, it may be necessary to modify your schema
+to change functionality. Once the changes are made to your schema in
+DBIx::Class, export the modified schema and the conversion scripts as
+in L</Creating DDL SQL>.
+
+B<Deploy update to customers>
+
+Add the L<DBIx::Class::Schema::Versioned> schema component to your
+Schema class. This will add a new table to your database called
+C<dbix_class_schema_vesion> which will keep track of which version is installed
+and warn if the user tries to run a newer schema version than the
+database thinks it has.
+
+Alternatively, you can send the conversion SQL scripts to your
+customers as above.
+
+=head2 Setting quoting for the generated SQL
+
+If the database contains column names with spaces and/or reserved words, they
+need to be quoted in the SQL queries. This is done using:
+
+ $schema->storage->sql_maker->quote_char([ qw/[ ]/] );
+ $schema->storage->sql_maker->name_sep('.');
+
+The first sets the quote characters. Either a pair of matching
+brackets, or a C<"> or C<'>:
-As your application evolves, it may be necessary to modify your schema to
-change functionality. Once the changes are made to your schema in DBIx::Class,
-export the modified schema as before, taking care not to overwrite the original:
+ $schema->storage->sql_maker->quote_char('"');
- sqlt --from SQL::Translator::DBIx::Class
- --to MySQL
- --DBIx::Class "Anything.pm" > Schema2.mysql.sql
+Check the documentation of your database for the correct quote
+characters to use. C<name_sep> needs to be set to allow the SQL
+generator to put the quotes the correct place.
-Next, use sqlt-diff to create an SQL script that will update the customer's
-database schema:
+In most cases you should set these as part of the arguments passed to
+L<DBIx::Class::Schema/connect>:
- sqlt-diff --to MySQL Schema1=MySQL Schema2=MySQL > SchemaUpdate.mysql.sql
+ my $schema = My::Schema->connect(
+ 'dbi:mysql:my_db',
+ 'db_user',
+ 'db_password',
+ {
+ quote_char => '"',
+ name_sep => '.'
+ }
+ )
-=head3 Deploy update to customers
+In some cases, quoting will be required for all users of a schema. To enforce
+this, you can also overload the C<connection> method for your schema class:
-The schema update can be deployed to customers using the same method as before.
+ sub connection {
+ my $self = shift;
+ my $rv = $self->next::method( @_ );
+ $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
+ $rv->storage->sql_maker->name_sep('.');
+ return $rv;
+ }
=head2 Setting limit dialect for SQL::Abstract::Limit
The JDBC bridge is one way of getting access to a MSSQL server from a platform
that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
-=head2 Setting quoting for the generated SQL.
+The limit dialect can also be set at connect time by specifying a
+C<limit_dialect> key in the final hash as shown above.
-If the database contains column names with spaces and/or reserved words, they
-need to be quoted in the SQL queries. This is done using:
+=head2 Working with PostgreSQL array types
- __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
- __PACKAGE__->storage->sql_maker->name_sep('.');
+You can also assign values to PostgreSQL array columns by passing array
+references in the C<\%columns> (C<\%vals>) hashref of the
+L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
+methods:
-The first sets the quote characters. Either a pair of matching
-brackets, or a C<"> or C<'>:
-
- __PACKAGE__->storage->sql_maker->quote_char('"');
+ $resultset->create({
+ numbers => [1, 2, 3]
+ });
-Check the documentation of your database for the correct quote
-characters to use. C<name_sep> needs to be set to allow the SQL
-generator to put the quotes the correct place.
+ $row->update(
+ {
+ numbers => [1, 2, 3]
+ },
+ {
+ day => '2008-11-24'
+ }
+ );
+
+In conditions (e.g. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
+methods) you cannot directly use array references (since this is interpreted as
+a list of values to be C<OR>ed), but you can use the following syntax to force
+passing them as bind values:
+
+ $resultset->search(
+ {
+ numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
+ }
+ );
+
+See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
+placeholders and bind values (subqueries)> for more explanation. Note that
+L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
+the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
+arrayrefs together with the column name, like this: C<< [column_name => value]
+>>.
+
+=head1 BOOTSTRAPPING/MIGRATING
+
+=head2 Easy migration from class-based to schema-based setup
+
+You want to start using the schema-based approach to L<DBIx::Class>
+(see L<SchemaIntro.pod>), but have an established class-based setup with lots
+of existing classes that you don't want to move by hand. Try this nifty script
+instead:
+
+ use MyDB;
+ use SQL::Translator;
+
+ my $schema = MyDB->schema_instance;
+
+ my $translator = SQL::Translator->new(
+ debug => $debug || 0,
+ trace => $trace || 0,
+ no_comments => $no_comments || 0,
+ show_warnings => $show_warnings || 0,
+ add_drop_table => $add_drop_table || 0,
+ validate => $validate || 0,
+ parser_args => {
+ 'DBIx::Schema' => $schema,
+ },
+ producer_args => {
+ 'prefix' => 'My::Schema',
+ },
+ );
+
+ $translator->parser('SQL::Translator::Parser::DBIx::Class');
+ $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
+
+ my $output = $translator->translate(@args) or die
+ "Error: " . $translator->error;
+
+ print $output;
+
+You could use L<Module::Find> to search for all subclasses in the MyDB::*
+namespace, which is currently left as an exercise for the reader.
-=head2 Overloading methods
+=head1 OVERLOADING METHODS
-L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
-method calls. You have to use calls to C<next::method> to overload methods.
-More information on using L<Class::C3> with L<DBIx::Class> can be found in
+L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
+method calls, useful for things like default values and triggers. You have to
+use calls to C<next::method> to overload methods. More information on using
+L<Class::C3> with L<DBIx::Class> can be found in
L<DBIx::Class::Manual::Component>.
-=head3 Changing one field whenever another changes
+=head2 Setting default values for a row
+
+It's as simple as overriding the C<new> method. Note the use of
+C<next::method>.
+
+ sub new {
+ my ( $class, $attrs ) = @_;
+
+ $attrs->{foo} = 'bar' unless defined $attrs->{foo};
+
+ my $new = $class->next::method($attrs);
+
+ return $new;
+ }
+
+For more information about C<next::method>, look in the L<Class::C3>
+documentation. See also L<DBIx::Class::Manual::Component> for more
+ways to write your own base classes to do this.
+
+People looking for ways to do "triggers" with DBIx::Class are probably
+just looking for this.
+
+=head2 Changing one field whenever another changes
-For example, say that you have three columns, C<id>, C<number>, and
+For example, say that you have three columns, C<id>, C<number>, and
C<squared>. You would like to make changes to C<number> and have
C<squared> be automagically set to the value of C<number> squared.
You can accomplish this by overriding C<store_column>:
Note that the hard work is done by the call to C<next::method>, which
redispatches your call to store_column in the superclass(es).
-=head3 Automatically creating related objects
+=head2 Automatically creating related objects
-You might have a class C<Artist> which has many C<CD>s. Further, if you
+You might have a class C<Artist> which has many C<CD>s. Further, you
want to create a C<CD> object every time you insert an C<Artist> object.
You can accomplish this by overriding C<insert> on your objects:
where C<fill_from_artist> is a method you specify in C<CD> which sets
values in C<CD> based on the data in the C<Artist> object you pass in.
-=head2 Debugging DBIx::Class objects with Data::Dumper
+=head2 Wrapping/overloading a column accessor
+
+B<Problem:>
+
+Say you have a table "Camera" and want to associate a description
+with each camera. For most cameras, you'll be able to generate the description from
+the other columns. However, in a few special cases you may want to associate a
+custom description with a camera.
+
+B<Solution:>
+
+In your database schema, define a description field in the "Camera" table that
+can contain text and null values.
+
+In DBIC, we'll overload the column accessor to provide a sane default if no
+custom description is defined. The accessor will either return or generate the
+description, depending on whether the field is null or not.
+
+First, in your "Camera" schema class, define the description field as follows:
+
+ __PACKAGE__->add_columns(description => { accessor => '_description' });
+
+Next, we'll define the accessor-wrapper subroutine:
+
+ sub description {
+ my $self = shift;
+
+ # If there is an update to the column, we'll let the original accessor
+ # deal with it.
+ return $self->_description(@_) if @_;
+
+ # Fetch the column value.
+ my $description = $self->_description;
+
+ # If there's something in the description field, then just return that.
+ return $description if defined $description && length $descripton;
+
+ # Otherwise, generate a description.
+ return $self->generate_description;
+ }
+
+=head1 DEBUGGING AND PROFILING
+
+=head2 DBIx::Class objects with Data::Dumper
L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
be hard to find the pertinent data in all the data it can generate.
will automagically clean up your data before printing it. See
L<Data::Dumper/EXAMPLES> for more information.
-=head2 Retrieving a row object's Schema
-
-It is possible to get a Schema object from a row object like so:
-
- my $schema = $cd->result_source->schema;
- # use the schema as normal:
- my $artist_rs = $schema->resultset('Artist');
-
-This can be useful when you don't want to pass around a Schema object to every
-method.
-
=head2 Profiling
When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
my $sql = shift();
my $params = @_;
- print "Executing $sql: ".join(', ', @params)."\n";
+ $self->print("Executing $sql: ".join(', ', @params)."\n");
$start = time();
}
my $sql = shift();
my @params = @_;
- printf("Execution took %0.4f seconds.\n", time() - $start);
+ my $elapsed = sprintf("%0.4f", time() - $start);
+ $self->print("Execution took $elapsed seconds.\n");
$start = undef;
}
You can then install that class as the debugging object:
- __PACKAGE__->storage()->debugobj(new My::Profiler());
- __PACKAGE__->storage()->debug(1);
+ __PACKAGE__->storage->debugobj(new My::Profiler());
+ __PACKAGE__->storage->debug(1);
A more complicated example might involve storing each execution of SQL in an
array:
You could then create average, high and low execution times for an SQL
statement and dig down to see if certain parameters cause aberrant behavior.
+You might want to check out L<DBIx::Class::QueryLog> as well.
-=head2 Getting the value of the primary key for the last database insert
+=head1 STARTUP SPEED
-AKA getting last_insert_id
+L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
+as the ORM loads all the relevant classes. This section examines
+techniques for reducing the startup delay.
-If you are using PK::Auto, this is straightforward:
+These tips are are listed in order of decreasing effectiveness - so the
+first tip, if applicable, should have the greatest effect on your
+application.
- my $foo = $rs->create(\%blah);
- # do more stuff
- my $id = $foo->id; # foo->my_primary_key_field will also work.
+=head2 Statically Define Your Schema
-If you are not using autoincrementing primary keys, this will probably
-not work, but then you already know the value of the last primary key anyway.
+If you are using
+L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
+classes dynamically based on the database schema then there will be a
+significant startup delay.
-=head2 Dynamic Sub-classing DBIx::Class proxy classes
-(AKA multi-class object inflation from one table)
-
-L<DBIx::Class> classes are proxy classes, therefore some different
-techniques need to be employed for more than basic subclassing. In
-this example we have a single user table that carries a boolean bit
-for admin. We would like like to give the admin users
-objects(L<DBIx::Class::Row>) the same methods as a regular user but
-also special admin only methods. It doesn't make sense to create two
-seperate proxy-class files for this. We would be copying all the user
-methods into the Admin class. There is a cleaner way to accomplish
-this.
+For production use a statically defined schema (which can be generated
+using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
+the database schema once - see
+L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
+L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
+details on creating static schemas from a database).
-Overriding the C<inflate_result> method within the User proxy-class
-gives us the effect we want. This method is called by
-L<DBIx::Class::ResultSet> when inflating a result from storage. So we
-grab the object being returned, inspect the values we are looking for,
-bless it if it's an admin object, and then return it. See the example
-below:
-
-B<Schema Definition>
-
- package DB::Schema;
-
- use base qw/DBIx::Class::Schema/;
-
- __PACKAGE__->load_classes(qw/User/);
-
-
-B<Proxy-Class definitions>
-
- package DB::Schema::User;
-
- use strict;
- use warnings;
- use base qw/DBIx::Class/;
-
- ### Defined what our admin class is for ensure_class_loaded
- my $admin_class = __PACKAGE__ . '::Admin';
-
- __PACKAGE__->load_components(qw/Core/);
-
- __PACKAGE__->table('users');
-
- __PACKAGE__->add_columns(qw/user_id email password
- firstname lastname active
- admin/);
-
- __PACKAGE__->set_primary_key('user_id');
-
- sub inflate_result {
- my $self = shift;
- my $ret = $self->next::method(@_);
- if( $ret->admin ) {### If this is an admin rebless for extra functions
- $self->ensure_class_loaded( $admin_class );
- bless $ret, $admin_class;
- }
- return $ret;
- }
-
- sub hello {
- print "I am a regular user.\n";
- return ;
- }
-
-
- package DB::Schema::User::Admin;
-
- use strict;
- use warnings;
- use base qw/DB::Schema::User/;
-
- sub hello
- {
- print "I am an admin.\n";
- return;
- }
-
- sub do_admin_stuff
- {
- print "I am doing admin stuff\n";
- return ;
- }
-
-B<Test File> test.pl
-
- use warnings;
- use strict;
- use DB::Schema;
-
- my $user_data = { email => 'someguy@place.com',
- password => 'pass1',
- admin => 0 };
-
- my $admin_data = { email => 'someadmin@adminplace.com',
- password => 'pass2',
- admin => 1 };
-
- my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
-
- $schema->resultset('User')->create( $user_data );
- $schema->resultset('User')->create( $admin_data );
-
- ### Now we search for them
- my $user = $schema->resultset('User')->single( $user_data );
- my $admin = $schema->resultset('User')->single( $admin_data );
-
- print ref $user, "\n";
- print ref $admin, "\n";
-
- print $user->password , "\n"; # pass1
- print $admin->password , "\n";# pass2; inherited from User
- print $user->hello , "\n";# I am a regular user.
- print $admin->hello, "\n";# I am an admin.
-
- ### The statement below will NOT print
- print "I can do admin stuff\n" if $user->can('do_admin_stuff');
- ### The statement below will print
- print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
+=head2 Move Common Startup into a Base Class
-=head2 Skip object creation for faster results
+Typically L<DBIx::Class> result classes start off with
-DBIx::Class is not built for speed, it's built for convenience and
-ease of use, but sometimes you just need to get the data, and skip the
-fancy objects.
-
-To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
-
- my $rs = $schema->resultset('CD');
-
- $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
-
- my $hash_ref = $rs->find(1);
-
-Wasn't that easy?
-
-=head2 Want to know if find_or_create found or created a row?
+ use base qw/DBIx::Class::Core/;
+ __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
-Just use C<find_or_new> instead, then check C<in_storage>:
+If this preamble is moved into a common base class:-
- my $obj = $rs->find_or_new({ blah => 'blarg' });
- unless ($obj->in_storage) {
- $obj->insert;
- # do whatever else you wanted if it was a new row
- }
+ package MyDBICbase;
-=head3 Wrapping/overloading a column accessor
+ use base qw/DBIx::Class::Core/;
+ __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
+ 1;
-Problem: Say you have a table "Camera" and want to associate a description
-with each camera. For most cameras, you'll be able to generate the description from
-the other columns. However, in a few special cases you may want to associate a
-custom description with a camera.
+and each result class then uses this as a base:-
-Solution:
+ use base qw/MyDBICbase/;
-In your database schema, define a description field in the "Camera" table that
-can contain text and null values.
+then the load_components is only performed once, which can result in a
+considerable startup speedup for schemas with many classes.
-In DBIC, we'll overload the column accessor to provide a sane default if no
-custom description is defined. The accessor will either return or generate the
-description, depending on whether the field is null or not.
+=head2 Explicitly List Schema Result Classes
-First, in your "Camera" schema class, define the description field as follows:
+The schema class will normally contain
- __PACKAGE__->add_columns(description => { accessor => '_description' });
+ __PACKAGE__->load_classes();
-Next, we'll define the accessor-wrapper subroutine:
+to load the result classes. This will use L<Module::Find|Module::Find>
+to find and load the appropriate modules. Explicitly defining the
+classes you wish to load will remove the overhead of
+L<Module::Find|Module::Find> and the related directory operations:
- sub description {
- my $self = shift;
+ __PACKAGE__->load_classes(qw/ CD Artist Track /);
- # If there is an update to the column, we'll let the original accessor
- # deal with it.
- return $self->_description(@_) if @_;
+If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
+syntax to load the appropriate classes there is not a direct alternative
+avoiding L<Module::Find|Module::Find>.
- # Fetch the column value.
- my $description = $self->_description;
+=head1 MEMORY USAGE
- # If there's something in the description field, then just return that.
- return $description if defined $description && length $descripton;
+=head2 Cached statements
- # Otherwise, generate a description.
- return $self->generate_description;
- }
+L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
+This is normally a good idea, but if too many statements are cached, the database may use too much
+memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
+to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
+
+ # print all currently cached prepared statements
+ print for keys %{$schema->storage->dbh->{CachedKids}};
+ # get a count of currently cached prepared statements
+ my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
+
+If it's appropriate, you can simply clear these statements, automatically deallocating them in the
+database:
+
+ my $kids = $schema->storage->dbh->{CachedKids};
+ delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
+
+But what you probably want is to expire unused statements and not those that are used frequently.
+You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
+
+ use Tie::Cache;
+ use DB::Main;
+ my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
+ on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },
+ });
=cut
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