my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db');
-=item 2. The B<resultset> method returns a ResultSet representing a query with no conditions on the given B<Source>:
+=item 2. The B<resultset> method returns a ResultSet representing a query with no conditions on the given B<ResultSource>:
my $user_resultset = $schema->resultset('User');
print $user->username;
-See the [DBIx::Class::Row]() documentation for more things you can do
+See the L<DBIx::Class::Row> documentation for more things you can do
with Row objects.
=head2 Simple SELECT, one row via the primary key
FROM users
WHERE username = 'fredbloggs';
-B<find> also works well on unique constraints, for example the username of our user. Unique constraints can be defined on Result classes using B<add_unique_constraint> (See L<CREATE|DBIx::Class::Manual::SQLHackers::CREATE>.
+B<find> also works well on unique constraints, for example the username of our user. Unique constraints can be defined on Result classes using B<add_unique_constraint> (See L<CREATE|DBIx::Class::Manual::SQLHackers::CREATE>).
=over
=back
-To run the query, use the B<all> or B<next> methods show at the beginning of this page.
+To run the query, use the B<all> or B<next> methods shown at the beginning of this page.
=head2 SELECT with different WHERE conditions
There's usually little reason to do this sort of query, as fetching all the data in a row doesn't cost any more time than fetching some of it. Unless of course your source is a View with calculations, or has huge blobs, or.. Okay, you might well want to do this occasionally.
+# this is completely false, is there a doc that states this that we need to fix?
+# find() takes all search() attributes, including things like prefetch
B<find> will always pull all the columns for the found row, so use the *search* method for this.
=over
=back
-Note that accessors for other columns not fetched will return B<undef>. To discover whether a columns data has been loaded or not, use the B<has_column_loaded> method.
+Note that accessors for other columns not fetched will return B<undef>, which is also the perl equivalent of the SQL C<NULL> value. To discover whether a columns data has been loaded or not, use L<DBIx::Class::Row/has_column_loaded>.
=head2 SELECT with aggregates
my $sum_prices_rs = $schema->resultset('Price')->search(
{ },
- { select => [ { SUM => 'amount'} ],
- as => [ 'sum_amount' ] }
+ { columns => { sum_amount => { SUM => 'amount'} } },
);
=back
my $posts_count_per_user = $schema->resultset('User')->search(
{ },
- { select => [ qw/id username posts.id posts.title/ ],
- as => [ qw/id username posts.id posts.title/ ],
+ { columns => [ qw/id username posts.id posts.title/ ],
join => 'posts',
}
);
JOIN posts posts ON posts.used_id = users.id
GROUP BY users.id, username;
-To group your results, use the B<group_by> attribute on a B<search> method. We also use the B<select> and B<as> attributes to select and name a subset of columns.
+To group your results, use the B<group_by> attribute on a B<search> method. We also use the B<columns> attribute to select and name a subset of columns.
=over
my $posts_count_per_user = $schema->resultset('User')->search(
{ },
- { select => [ qw/id username/, { count => 'posts.id' } ],
- as => [ qw/id username post_count/ ],
+ { columns => [ qw/id username/, { post_count => { count => 'posts.id' } } ],
join => 'posts',
group_by => [qw/id username/],
}
=item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to sort data on:
+# this will not collapse results (you will get users * (amount of posts || 1) as a result, sure you want to showcase this?
my $sorted_users = $schema->resultset('User')->search(
{ },
- { '+select' => [ qw/posts.id posts.title/ ],
- '+as' => [ qw/posts.id posts.title/ ],
+ { '+columns' => [ qw/posts.id posts.title/ ],
join => 'posts',
order_by => [qw/username posts.title/],
}
The results will be ordered by username, then post title, ready for outputting.
-Note how we have added the title of each post, this prevents us having to fire off a second query to fetch the post data to output it. The B<+select> attribute specifies an extended set of columns to fetch, in addition to the columns of the main query table.
+Note how we have added the title of each post, this prevents us having to fire off a second query to fetch the post data to output it. The B<+columns> attribute specifies an extended set of columns to fetch, in addition to the columns of the main query table.
To retrieve the extra data, call the usual relationship accessor:
SELECT users.id, username, dob
FROM users
JOIN posts posts ON posts.used_id = users.id
- GROUP BY users.id, username;
+ GROUP BY users.id, username, dob
HAVING count(posts.id) = 1
To add a B<having> clause to your query, use the corresponding B<having> attribute.
my $filtered_users = $schema->resultset('User')->search(
{ },
- { '+select' => [ qw/me.id me.username me.dob/ ],
- '+as' => [ qw/me.id me.username me.dob/ ],
+ { 'columns' => [ qw/me.id me.username me.dob/ ],
join => 'posts',
- group_by => [qw/me.id me.username/],
+ group_by => [qw/me.id me.username me.dob/],
having => [{ 'posts.id' => 1 }],
}
);
SELECT DISTINCT(posts.title)
FROM posts
-DBIx::Class doesn't currently produce a B<DISTINCT> keyword, but will output a B<GROUP BY> to simulate the same effect.
+To produce DISTINCT clauses, we need to use a hashref argument to the list of items passed to the B<columns> attribute.
=over
my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db');
-=item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to group data on:
+=item 2. Call the B<search> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to find distinct rows on:
my $distinct_posts = $schema->resultset('Post')->search(
{ },
- { columns => ['me.title'],
- distinct => 1,
+ { columns => [{ 'd_title' => { distinct => 'me.title' } }],
}
);
=back
-This actually outputs:
+This can also be achieved by using the ResultSet method B<get_column>. The method returns a ResultSetColumn object based on the given column name argument, which can call SQL aggregate functions based upon the column of that data.
- SELECT posts.title
- FROM posts
- GROUP BY posts.title
+So we can also do this, for single column DISTINCT clauses:
+
+=over
+
+=item 1. Create a Schema object representing the database you are working with:
+
+ my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db');
+
+=item 2. Call the B<get_column> method on the resultset of the L<ResultSource|DBIx::Class::ResultSource> you wish to find distinct rows on:
+
+ my $rs_column = $schema->resultset('Post')->get_column('title');
+
+=item 3. Call the B<func> method on the resultset column object and pass it the name of the function to apply:
+
+ my $titles = $rs_column->func('distinct');
+
+=back
+
+The result will be an arrayref of the actual values. If a ResultSet object is needed for further refinement, use B<func_rs> instead.
=head2 SELECT ... FOR UPDATE
The resultset and rows will be returned as normal, and can be used to update the rows without worrying about other
-=head2 SELECT with LIMIT
+=head2 SELECT with LIMIT and OFFSET
SELECT users.id, users.username
FROM users
ORDER BY user.dob DESC
- LIMIT 10;
+ LIMIT 10 OFFSET 11;
-To reduce the set or rows fetched, use the B<rows> attribute.
+To reduce the set of rows fetched, use the B<rows> and B<page> attributes. The value of B<page> will default to 1, which means no OFFSET will be applied.
=over
{ columns => [qw/me.id me.username/],
order_by => { '-desc' => ['user.dob'] },
rows => 10,
+ page => 2,
}
);
-This will return exactly 10 row objects, sorted by descending date of birth of the users.
+This will return exactly 10 row objects, sorted by descending date of birth of the users, starting at the 11th row of the sorted result.
=back
projects / dbsrgits/DBIx-Class-Manual-SQLHackers.git / blobdiff