[dbsrgits/DBIx-Class.git] / lib / DBIx / Class / ResultSource.pm

package DBIx::Class::ResultSource;

use strict;
use warnings;

use DBIx::Class::ResultSet;
use DBIx::Class::ResultSourceHandle;
use Carp::Clan qw/^DBIx::Class/;
use Storable;

use base qw/DBIx::Class/;

__PACKAGE__->mk_group_accessors('simple' => qw/_ordered_columns
  _columns _primaries _unique_constraints name resultset_attributes
  schema from _relationships column_info_from_storage source_info
  source_name sqlt_deploy_callback/);

__PACKAGE__->mk_group_accessors('component_class' => qw/resultset_class
  result_class/);

=head1 NAME

DBIx::Class::ResultSource - Result source object

=head1 SYNOPSIS

=head1 DESCRIPTION

A ResultSource is a component of a schema from which results can be directly
retrieved, most usually a table (see L<DBIx::Class::ResultSource::Table>)

Basic view support also exists, see L<<DBIx::Class::ResultSource::View>.

=head1 METHODS

=pod

=cut

sub new {
  my ($class, $attrs) = @_;
  $class = ref $class if ref $class;

  my $new = bless { %{$attrs || {}} }, $class;
  $new->{resultset_class} ||= 'DBIx::Class::ResultSet';
  $new->{resultset_attributes} = { %{$new->{resultset_attributes} || {}} };
  $new->{_ordered_columns} = [ @{$new->{_ordered_columns}||[]}];
  $new->{_columns} = { %{$new->{_columns}||{}} };
  $new->{_relationships} = { %{$new->{_relationships}||{}} };
  $new->{name} ||= "!!NAME NOT SET!!";
  $new->{_columns_info_loaded} ||= 0;
  $new->{sqlt_deploy_callback} ||= "default_sqlt_deploy_hook";
  return $new;
}

=pod

=head2 add_columns

=over

=item Arguments: @columns

=item Return value: The ResultSource object

=back

  $source->add_columns(qw/col1 col2 col3/);

  $source->add_columns('col1' => \%col1_info, 'col2' => \%col2_info, ...);

Adds columns to the result source. If supplied key => hashref pairs, uses
the hashref as the column_info for that column. Repeated calls of this
method will add more columns, not replace them.

The column names given will be created as accessor methods on your
L<DBIx::Class::Row> objects. You can change the name of the accessor
by supplying an L</accessor> in the column_info hash.

The contents of the column_info are not set in stone. The following
keys are currently recognised/used by DBIx::Class:

=over 4

=item accessor

Use this to set the name of the accessor method for this column. If unset,
the name of the column will be used.

=item data_type

This contains the column type. It is automatically filled by the
L<SQL::Translator::Producer::DBIx::Class::File> producer, and the
L<DBIx::Class::Schema::Loader> module. If you do not enter a
data_type, DBIx::Class will attempt to retrieve it from the
database for you, using L<DBI>'s column_info method. The values of this
key are typically upper-cased.

Currently there is no standard set of values for the data_type. Use
whatever your database supports.

=item size

The length of your column, if it is a column type that can have a size
restriction. This is currently only used by L<DBIx::Class::Schema/deploy>.

=item is_nullable

Set this to a true value for a columns that is allowed to contain
NULL values. This is currently only used by L<DBIx::Class::Schema/deploy>.

=item is_auto_increment

Set this to a true value for a column whose value is somehow
automatically set. This is used to determine which columns to empty
when cloning objects using C<copy>. It is also used by
L<DBIx::Class::Schema/deploy>.

=item is_foreign_key

Set this to a true value for a column that contains a key from a
foreign table. This is currently only used by
L<DBIx::Class::Schema/deploy>.

=item default_value

Set this to the default value which will be inserted into a column
by the database. Can contain either a value or a function (use a
reference to a scalar e.g. C<\'now()'> if you want a function). This
is currently only used by L<DBIx::Class::Schema/deploy>.

=item sequence

Set this on a primary key column to the name of the sequence used to
generate a new key value. If not specified, L<DBIx::Class::PK::Auto>
will attempt to retrieve the name of the sequence from the database
automatically.

=item auto_nextval

Set this to a true value for a column whose value is retrieved
automatically from an oracle sequence. If you do not use an Oracle
trigger to get the nextval, you have to set sequence as well.

=item extra

This is used by L<DBIx::Class::Schema/deploy> and L<SQL::Translator>
to add extra non-generic data to the column. For example: C<< extra
=> { unsigned => 1} >> is used by the MySQL producer to set an integer
column to unsigned. For more details, see
L<SQL::Translator::Producer::MySQL>.

=back

=head2 add_column

=over

=item Arguments: $colname, [ \%columninfo ]

=item Return value: 1/0 (true/false)

=back

  $source->add_column('col' => \%info?);

Add a single column and optional column info. Uses the same column
info keys as L</add_columns>.

=cut

sub add_columns {
  my ($self, @cols) = @_;
  $self->_ordered_columns(\@cols) unless $self->_ordered_columns;

  my @added;
  my $columns = $self->_columns;
  while (my $col = shift @cols) {
    # If next entry is { ... } use that for the column info, if not
    # use an empty hashref
    my $column_info = ref $cols[0] ? shift(@cols) : {};
    push(@added, $col) unless exists $columns->{$col};
    $columns->{$col} = $column_info;
  }
  push @{ $self->_ordered_columns }, @added;
  return $self;
}

sub add_column { shift->add_columns(@_); } # DO NOT CHANGE THIS TO GLOB

=head2 has_column

=over

=item Arguments: $colname

=item Return value: 1/0 (true/false)

=back

  if ($source->has_column($colname)) { ... }

Returns true if the source has a column of this name, false otherwise.

=cut

sub has_column {
  my ($self, $column) = @_;
  return exists $self->_columns->{$column};
}

=head2 column_info

=over

=item Arguments: $colname

=item Return value: Hashref of info

=back

  my $info = $source->column_info($col);

Returns the column metadata hashref for a column, as originally passed
to L</add_columns>. See the description of L</add_columns> for information
on the contents of the hashref.

=cut

sub column_info {
  my ($self, $column) = @_;
  $self->throw_exception("No such column $column")
    unless exists $self->_columns->{$column};
  #warn $self->{_columns_info_loaded}, "\n";
  if ( ! $self->_columns->{$column}{data_type}
       and $self->column_info_from_storage
       and ! $self->{_columns_info_loaded}
       and $self->schema and $self->storage )
  {
    $self->{_columns_info_loaded}++;
    my $info = {};
    my $lc_info = {};
    # eval for the case of storage without table
    eval { $info = $self->storage->columns_info_for( $self->from ) };
    unless ($@) {
      for my $realcol ( keys %{$info} ) {
        $lc_info->{lc $realcol} = $info->{$realcol};
      }
      foreach my $col ( keys %{$self->_columns} ) {
        $self->_columns->{$col} = {
          %{ $self->_columns->{$col} },
          %{ $info->{$col} || $lc_info->{lc $col} || {} }
        };
      }
    }
  }
  return $self->_columns->{$column};
}

=head2 columns

=over

=item Arguments: None

=item Return value: Ordered list of column names

=back

  my @column_names = $source->columns;

Returns all column names in the order they were declared to L</add_columns>.

=cut

sub columns {
  my $self = shift;
  $self->throw_exception(
    "columns() is a read-only accessor, did you mean add_columns()?"
  ) if (@_ > 1);
  return @{$self->{_ordered_columns}||[]};
}

=head2 remove_columns

=over

=item Arguments: @colnames

=item Return value: undefined

=back

  $source->remove_columns(qw/col1 col2 col3/);

Removes the given list of columns by name, from the result source.

B<Warning>: Removing a column that is also used in the sources primary
key, or in one of the sources unique constraints, B<will> result in a
broken result source.

=head2 remove_column

=over

=item Arguments: $colname

=item Return value: undefined

=back

  $source->remove_column('col');

Remove a single column by name from the result source, similar to
L</remove_columns>.

B<Warning>: Removing a column that is also used in the sources primary
key, or in one of the sources unique constraints, B<will> result in a
broken result source.

=cut

sub remove_columns {
  my ($self, @to_remove) = @_;

  my $columns = $self->_columns
    or return;

  my %to_remove;
  for (@to_remove) {
    delete $columns->{$_};
    ++$to_remove{$_};
  }

  $self->_ordered_columns([ grep { not $to_remove{$_} } @{$self->_ordered_columns} ]);
}

sub remove_column { shift->remove_columns(@_); } # DO NOT CHANGE THIS TO GLOB

=head2 set_primary_key

=over 4

=item Arguments: @cols

=item Return value: undefined

=back

Defines one or more columns as primary key for this source. Should be
called after L</add_columns>.

Additionally, defines a L<unique constraint|add_unique_constraint>
named C<primary>.

The primary key columns are used by L<DBIx::Class::PK::Auto> to
retrieve automatically created values from the database.

=cut

sub set_primary_key {
  my ($self, @cols) = @_;
  # check if primary key columns are valid columns
  foreach my $col (@cols) {
    $self->throw_exception("No such column $col on table " . $self->name)
      unless $self->has_column($col);
  }
  $self->_primaries(\@cols);

  $self->add_unique_constraint(primary => \@cols);
}

=head2 primary_columns

=over 4

=item Arguments: None

=item Return value: Ordered list of primary column names

=back

Read-only accessor which returns the list of primary keys, supplied by
L</set_primary_key>.

=cut

sub primary_columns {
  return @{shift->_primaries||[]};
}

=head2 add_unique_constraint

=over 4

=item Arguments: [ $name ], \@colnames

=item Return value: undefined

=back

Declare a unique constraint on this source. Call once for each unique
constraint.

  # For UNIQUE (column1, column2)
  __PACKAGE__->add_unique_constraint(
    constraint_name => [ qw/column1 column2/ ],
  );

Alternatively, you can specify only the columns:

  __PACKAGE__->add_unique_constraint([ qw/column1 column2/ ]);

This will result in a unique constraint named C<table_column1_column2>, where
C<table> is replaced with the table name.

Unique constraints are used, for example, when you call
L<DBIx::Class::ResultSet/find>. Only columns in the constraint are searched.

Throws an error if any of the given column names do not yet exist on
the result source.

=cut

sub add_unique_constraint {
  my $self = shift;
  my $cols = pop @_;
  my $name = shift;

  $name ||= $self->name_unique_constraint($cols);

  foreach my $col (@$cols) {
    $self->throw_exception("No such column $col on table " . $self->name)
      unless $self->has_column($col);
  }

  my %unique_constraints = $self->unique_constraints;
  $unique_constraints{$name} = $cols;
  $self->_unique_constraints(\%unique_constraints);
}

=head2 name_unique_constraint

=over 4

=item Arguments: @colnames

=item Return value: Constraint name

=back

  $source->table('mytable');
  $source->name_unique_constraint('col1', 'col2');
  # returns
  'mytable_col1_col2'

Return a name for a unique constraint containing the specified
columns. The name is created by joining the table name and each column
name, using an underscore character.

For example, a constraint on a table named C<cd> containing the columns
C<artist> and C<title> would result in a constraint name of C<cd_artist_title>.

This is used by L</add_unique_constraint> if you do not specify the
optional constraint name.

=cut

sub name_unique_constraint {
  my ($self, $cols) = @_;

  return join '_', $self->name, @$cols;
}

=head2 unique_constraints

=over 4

=item Arguments: None

=item Return value: Hash of unique constraint data

=back

  $source->unique_constraints();

Read-only accessor which returns a hash of unique constraints on this source.

The hash is keyed by constraint name, and contains an arrayref of
column names as values.

=cut

sub unique_constraints {
  return %{shift->_unique_constraints||{}};
}

=head2 unique_constraint_names

=over 4

=item Arguments: None

=item Return value: Unique constraint names

=back

  $source->unique_constraint_names();

Returns the list of unique constraint names defined on this source.

=cut

sub unique_constraint_names {
  my ($self) = @_;

  my %unique_constraints = $self->unique_constraints;

  return keys %unique_constraints;
}

=head2 unique_constraint_columns

=over 4

=item Arguments: $constraintname

=item Return value: List of constraint columns

=back

  $source->unique_constraint_columns('myconstraint');

Returns the list of columns that make up the specified unique constraint.

=cut

sub unique_constraint_columns {
  my ($self, $constraint_name) = @_;

  my %unique_constraints = $self->unique_constraints;

  $self->throw_exception(
    "Unknown unique constraint $constraint_name on '" . $self->name . "'"
  ) unless exists $unique_constraints{$constraint_name};

  return @{ $unique_constraints{$constraint_name} };
}

=head2 sqlt_deploy_callback

=over

=item Arguments: $callback

=back

  __PACKAGE__->sqlt_deploy_callback('mycallbackmethod');

An accessor to set a callback to be called during deployment of
the schema via L<DBIx::Class::Schema/create_ddl_dir> or
L<DBIx::Class::Schema/deploy>.

The callback can be set as either a code reference or the name of a
method in the current result class.

If not set, the L</default_sqlt_deploy_hook> is called.

Your callback will be passed the $source object representing the
ResultSource instance being deployed, and the
L<SQL::Translator::Schema::Table> object being created from it. The
callback can be used to manipulate the table object or add your own
customised indexes. If you need to manipulate a non-table object, use
the L<DBIx::Class::Schema/sqlt_deploy_hook>.

See L<DBIx::Class::Manual::Cookbook/Adding Indexes And Functions To
Your SQL> for examples.

This sqlt deployment callback can only be used to manipulate
SQL::Translator objects as they get turned into SQL. To execute
post-deploy statements which SQL::Translator does not currently
handle, override L<DBIx::Class::Schema/deploy> in your Schema class
and call L<dbh_do|DBIx::Class::Storage::DBI/dbh_do>.

=head2 default_sqlt_deploy_hook

=over

=item Arguments: $source, $sqlt_table

=item Return value: undefined

=back

This is the sensible default for L</sqlt_deploy_callback>.

If a method named C<sqlt_deploy_hook> exists in your Result class, it
will be called and passed the current C<$source> and the
C<$sqlt_table> being deployed.

=cut

sub default_sqlt_deploy_hook {
  my $self = shift;

  my $class = $self->result_class;

  if ($class and $class->can('sqlt_deploy_hook')) {
    $class->sqlt_deploy_hook(@_);
  }
}

sub _invoke_sqlt_deploy_hook {
  my $self = shift;
  if ( my $hook = $self->sqlt_deploy_callback) {
    $self->$hook(@_);
  }
}

=head2 resultset

=over 4

=item Arguments: None

=item Return value: $resultset

=back

Returns a resultset for the given source. This will initially be created
on demand by calling

  $self->resultset_class->new($self, $self->resultset_attributes)

but is cached from then on unless resultset_class changes.

=head2 resultset_class

=over 4

=item Arguments: $classname

=item Return value: $classname

=back

  package My::ResultSetClass;
  use base 'DBIx::Class::ResultSet';
  ...

  $source->resultset_class('My::ResultSet::Class');

Set the class of the resultset. This is useful if you want to create your
own resultset methods. Create your own class derived from
L<DBIx::Class::ResultSet>, and set it here. If called with no arguments,
this method returns the name of the existing resultset class, if one
exists.

=head2 resultset_attributes

=over 4

=item Arguments: \%attrs

=item Return value: \%attrs

=back

  $source->resultset_attributes({ order_by => [ 'id' ] });

Store a collection of resultset attributes, that will be set on every
L<DBIx::Class::ResultSet> produced from this result source. For a full
list see L<DBIx::Class::ResultSet/ATTRIBUTES>.

=cut

sub resultset {
  my $self = shift;
  $self->throw_exception(
    'resultset does not take any arguments. If you want another resultset, '.
    'call it on the schema instead.'
  ) if scalar @_;

  return $self->resultset_class->new(
    $self,
    {
      %{$self->{resultset_attributes}},
      %{$self->schema->default_resultset_attributes}
    },
  );
}

=head2 source_name

=over 4

=item Arguments: $source_name

=item Result value: $source_name

=back

Set an alternate name for the result source when it is loaded into a schema.
This is useful if you want to refer to a result source by a name other than
its class name.

  package ArchivedBooks;
  use base qw/DBIx::Class/;
  __PACKAGE__->table('books_archive');
  __PACKAGE__->source_name('Books');

  # from your schema...
  $schema->resultset('Books')->find(1);

=head2 from

=over 4

=item Arguments: None

=item Return value: FROM clause

=back

  my $from_clause = $source->from();

Returns an expression of the source to be supplied to storage to specify
retrieval from this source. In the case of a database, the required FROM
clause contents.

=head2 schema

=over 4

=item Arguments: None

=item Return value: A schema object

=back

  my $schema = $source->schema();

Returns the L<DBIx::Class::Schema> object that this result source 
belongs to.

=head2 storage

=over 4

=item Arguments: None

=item Return value: A Storage object

=back

  $source->storage->debug(1);

Returns the storage handle for the current schema.

See also: L<DBIx::Class::Storage>

=cut

sub storage { shift->schema->storage; }

=head2 add_relationship

=over 4

=item Arguments: $relname, $related_source_name, \%cond, [ \%attrs ]

=item Return value: 1/true if it succeeded

=back

  $source->add_relationship('relname', 'related_source', $cond, $attrs);

L<DBIx::Class::Relationship> describes a series of methods which
create pre-defined useful types of relationships. Look there first
before using this method directly.

The relationship name can be arbitrary, but must be unique for each
relationship attached to this result source. 'related_source' should
be the name with which the related result source was registered with
the current schema. For example:

  $schema->source('Book')->add_relationship('reviews', 'Review', {
    'foreign.book_id' => 'self.id',
  });

The condition C<$cond> needs to be an L<SQL::Abstract>-style
representation of the join between the tables. For example, if you're
creating a relation from Author to Book,

  { 'foreign.author_id' => 'self.id' }

will result in the JOIN clause

  author me JOIN book foreign ON foreign.author_id = me.id

You can specify as many foreign => self mappings as necessary.

Valid attributes are as follows:

=over 4

=item join_type

Explicitly specifies the type of join to use in the relationship. Any
SQL join type is valid, e.g. C<LEFT> or C<RIGHT>. It will be placed in
the SQL command immediately before C<JOIN>.

=item proxy

An arrayref containing a list of accessors in the foreign class to proxy in
the main class. If, for example, you do the following:

  CD->might_have(liner_notes => 'LinerNotes', undef, {
    proxy => [ qw/notes/ ],
  });

Then, assuming LinerNotes has an accessor named notes, you can do:

  my $cd = CD->find(1);
  # set notes -- LinerNotes object is created if it doesn't exist
  $cd->notes('Notes go here');

=item accessor

Specifies the type of accessor that should be created for the
relationship. Valid values are C<single> (for when there is only a single
related object), C<multi> (when there can be many), and C<filter> (for
when there is a single related object, but you also want the relationship
accessor to double as a column accessor). For C<multi> accessors, an
add_to_* method is also created, which calls C<create_related> for the
relationship.

=back

Throws an exception if the condition is improperly supplied, or cannot
be resolved using L</resolve_join>.

=cut

sub add_relationship {
  my ($self, $rel, $f_source_name, $cond, $attrs) = @_;
  $self->throw_exception("Can't create relationship without join condition")
    unless $cond;
  $attrs ||= {};

  # Check foreign and self are right in cond
  if ( (ref $cond ||'') eq 'HASH') {
    for (keys %$cond) {
      $self->throw_exception("Keys of condition should be of form 'foreign.col', not '$_'")
        if /\./ && !/^foreign\./;
    }
  }

  my %rels = %{ $self->_relationships };
  $rels{$rel} = { class => $f_source_name,
                  source => $f_source_name,
                  cond  => $cond,
                  attrs => $attrs };
  $self->_relationships(\%rels);

  return $self;

  # XXX disabled. doesn't work properly currently. skip in tests.

  my $f_source = $self->schema->source($f_source_name);
  unless ($f_source) {
    $self->ensure_class_loaded($f_source_name);
    $f_source = $f_source_name->result_source;
    #my $s_class = ref($self->schema);
    #$f_source_name =~ m/^${s_class}::(.*)$/;
    #$self->schema->register_class(($1 || $f_source_name), $f_source_name);
    #$f_source = $self->schema->source($f_source_name);
  }
  return unless $f_source; # Can't test rel without f_source

  eval { $self->resolve_join($rel, 'me') };

  if ($@) { # If the resolve failed, back out and re-throw the error
    delete $rels{$rel}; #
    $self->_relationships(\%rels);
    $self->throw_exception("Error creating relationship $rel: $@");
  }
  1;
}

=head2 relationships

=over 4

=item Arguments: None

=item Return value: List of relationship names

=back

  my @relnames = $source->relationships();

Returns all relationship names for this source.

=cut

sub relationships {
  return keys %{shift->_relationships};
}

=head2 relationship_info

=over 4

=item Arguments: $relname

=item Return value: Hashref of relation data,

=back

Returns a hash of relationship information for the specified relationship
name. The keys/values are as specified for L</add_relationship>.

=cut

sub relationship_info {
  my ($self, $rel) = @_;
  return $self->_relationships->{$rel};
}

=head2 has_relationship

=over 4

=item Arguments: $rel

=item Return value: 1/0 (true/false)

=back

Returns true if the source has a relationship of this name, false otherwise.

=cut

sub has_relationship {
  my ($self, $rel) = @_;
  return exists $self->_relationships->{$rel};
}

=head2 reverse_relationship_info

=over 4

=item Arguments: $relname

=item Return value: Hashref of relationship data

=back

Looks through all the relationships on the source this relationship
points to, looking for one whose condition is the reverse of the
condition on this relationship.

A common use of this is to find the name of the C<belongs_to> relation
opposing a C<has_many> relation. For definition of these look in
L<DBIx::Class::Relationship>.

The returned hashref is keyed by the name of the opposing
relationship, and contains it's data in the same manner as
L</relationship_info>.

=cut

sub reverse_relationship_info {
  my ($self, $rel) = @_;
  my $rel_info = $self->relationship_info($rel);
  my $ret = {};

  return $ret unless ((ref $rel_info->{cond}) eq 'HASH');

  my @cond = keys(%{$rel_info->{cond}});
  my @refkeys = map {/^\w+\.(\w+)$/} @cond;
  my @keys = map {$rel_info->{cond}->{$_} =~ /^\w+\.(\w+)$/} @cond;

  # Get the related result source for this relationship
  my $othertable = $self->related_source($rel);

  # Get all the relationships for that source that related to this source
  # whose foreign column set are our self columns on $rel and whose self
  # columns are our foreign columns on $rel.
  my @otherrels = $othertable->relationships();
  my $otherrelationship;
  foreach my $otherrel (@otherrels) {
    my $otherrel_info = $othertable->relationship_info($otherrel);

    my $back = $othertable->related_source($otherrel);
    next unless $back->source_name eq $self->source_name;

    my @othertestconds;

    if (ref $otherrel_info->{cond} eq 'HASH') {
      @othertestconds = ($otherrel_info->{cond});
    }
    elsif (ref $otherrel_info->{cond} eq 'ARRAY') {
      @othertestconds = @{$otherrel_info->{cond}};
    }
    else {
      next;
    }

    foreach my $othercond (@othertestconds) {
      my @other_cond = keys(%$othercond);
      my @other_refkeys = map {/^\w+\.(\w+)$/} @other_cond;
      my @other_keys = map {$othercond->{$_} =~ /^\w+\.(\w+)$/} @other_cond;
      next if (!$self->compare_relationship_keys(\@refkeys, \@other_keys) ||
               !$self->compare_relationship_keys(\@other_refkeys, \@keys));
      $ret->{$otherrel} =  $otherrel_info;
    }
  }
  return $ret;
}

=head2 compare_relationship_keys

=over 4

=item Arguments: \@keys1, \@keys2

=item Return value: 1/0 (true/false)

=back

Returns true if both sets of keynames are the same, false otherwise.

=cut

sub compare_relationship_keys {
  my ($self, $keys1, $keys2) = @_;

  # Make sure every keys1 is in keys2
  my $found;
  foreach my $key (@$keys1) {
    $found = 0;
    foreach my $prim (@$keys2) {
      if ($prim eq $key) {
        $found = 1;
        last;
      }
    }
    last unless $found;
  }

  # Make sure every key2 is in key1
  if ($found) {
    foreach my $prim (@$keys2) {
      $found = 0;
      foreach my $key (@$keys1) {
        if ($prim eq $key) {
          $found = 1;
          last;
        }
      }
      last unless $found;
    }
  }

  return $found;
}

=head2 resolve_join

=over 4

=item Arguments: $relation

=item Return value: Join condition arrayref

=back

Returns the join structure required for the related result source.

=cut

sub resolve_join {
  my ($self, $join, $alias, $seen, $force_left) = @_;
  $seen ||= {};
  $force_left ||= { force => 0 };
  if (ref $join eq 'ARRAY') {
    return map { $self->resolve_join($_, $alias, $seen) } @$join;
  } elsif (ref $join eq 'HASH') {
    return
      map {
        my $as = ($seen->{$_} ? $_.'_'.($seen->{$_}+1) : $_);
        local $force_left->{force};
        (
          $self->resolve_join($_, $alias, $seen, $force_left),
          $self->related_source($_)->resolve_join(
            $join->{$_}, $as, $seen, $force_left
          )
        );
      } keys %$join;
  } elsif (ref $join) {
    $self->throw_exception("No idea how to resolve join reftype ".ref $join);
  } else {
    my $count = ++$seen->{$join};
    #use Data::Dumper; warn Dumper($seen);
    my $as = ($count > 1 ? "${join}_${count}" : $join);
    my $rel_info = $self->relationship_info($join);
    $self->throw_exception("No such relationship ${join}") unless $rel_info;
    my $type;
    if ($force_left->{force}) {
      $type = 'left';
    } else {
      $type = $rel_info->{attrs}{join_type} || '';
      $force_left->{force} = 1 if lc($type) eq 'left';
    }
    return [ { $as => $self->related_source($join)->from,
               -join_type => $type },
             $self->resolve_condition($rel_info->{cond}, $as, $alias) ];
  }
}

=head2 pk_depends_on

=over 4

=item Arguments: $relname, $rel_data

=item Return value: 1/0 (true/false)

=back

Determines whether a relation is dependent on an object from this source
having already been inserted. Takes the name of the relationship and a
hashref of columns of the related object.

=cut

sub pk_depends_on {
  my ($self, $relname, $rel_data) = @_;
  my $cond = $self->relationship_info($relname)->{cond};

  return 0 unless ref($cond) eq 'HASH';

  # map { foreign.foo => 'self.bar' } to { bar => 'foo' }

  my $keyhash = { map { my $x = $_; $x =~ s/.*\.//; $x; } reverse %$cond };

  # assume anything that references our PK probably is dependent on us
  # rather than vice versa, unless the far side is (a) defined or (b)
  # auto-increment

  my $rel_source = $self->related_source($relname);

  foreach my $p ($self->primary_columns) {
    if (exists $keyhash->{$p}) {
      unless (defined($rel_data->{$keyhash->{$p}})
              || $rel_source->column_info($keyhash->{$p})
                            ->{is_auto_increment}) {
        return 0;
      }
    }
  }

  return 1;
}

=head2 resolve_condition

=over 4

=item Arguments: $cond, $as, $alias|$object

=back

Resolves the passed condition to a concrete query fragment. If given an alias,
returns a join condition; if given an object, inverts that object to produce
a related conditional from that object.

=cut

our $UNRESOLVABLE_CONDITION = \'1 = 0';

sub resolve_condition {
  my ($self, $cond, $as, $for) = @_;
  #warn %$cond;
  if (ref $cond eq 'HASH') {
    my %ret;
    foreach my $k (keys %{$cond}) {
      my $v = $cond->{$k};
      # XXX should probably check these are valid columns
      $k =~ s/^foreign\.// ||
        $self->throw_exception("Invalid rel cond key ${k}");
      $v =~ s/^self\.// ||
        $self->throw_exception("Invalid rel cond val ${v}");
      if (ref $for) { # Object
        #warn "$self $k $for $v";
        unless ($for->has_column_loaded($v)) {
          if ($for->in_storage) {
            $self->throw_exception("Column ${v} not loaded on ${for} trying to resolve relationship");
          }
          return $UNRESOLVABLE_CONDITION;
        }
        $ret{$k} = $for->get_column($v);
        #$ret{$k} = $for->get_column($v) if $for->has_column_loaded($v);
        #warn %ret;
      } elsif (!defined $for) { # undef, i.e. "no object"
        $ret{$k} = undef;
      } elsif (ref $as eq 'HASH') { # reverse hashref
        $ret{$v} = $as->{$k};
      } elsif (ref $as) { # reverse object
        $ret{$v} = $as->get_column($k);
      } elsif (!defined $as) { # undef, i.e. "no reverse object"
        $ret{$v} = undef;
      } else {
        $ret{"${as}.${k}"} = "${for}.${v}";
      }
    }
    return \%ret;
  } elsif (ref $cond eq 'ARRAY') {
    return [ map { $self->resolve_condition($_, $as, $for) } @$cond ];
  } else {
   die("Can't handle this yet :(");
  }
}

=head2 resolve_prefetch

=over 4

=item Arguments: hashref/arrayref/scalar

=back

Accepts one or more relationships for the current source and returns an
array of column names for each of those relationships. Column names are
prefixed relative to the current source, in accordance with where they appear
in the supplied relationships. Examples:

  my $source = $schema->resultset('Tag')->source;
  @columns = $source->resolve_prefetch( { cd => 'artist' } );

  # @columns =
  #(
  #  'cd.cdid',
  #  'cd.artist',
  #  'cd.title',
  #  'cd.year',
  #  'cd.artist.artistid',
  #  'cd.artist.name'
  #)

  @columns = $source->resolve_prefetch( qw[/ cd /] );

  # @columns =
  #(
  #   'cd.cdid',
  #   'cd.artist',
  #   'cd.title',
  #   'cd.year'
  #)

  $source = $schema->resultset('CD')->source;
  @columns = $source->resolve_prefetch( qw[/ artist producer /] );

  # @columns =
  #(
  #  'artist.artistid',
  #  'artist.name',
  #  'producer.producerid',
  #  'producer.name'
  #)

=cut

sub resolve_prefetch {
  my ($self, $pre, $alias, $seen, $order, $collapse) = @_;
  $seen ||= {};
  #$alias ||= $self->name;
  #warn $alias, Dumper $pre;
  if( ref $pre eq 'ARRAY' ) {
    return
      map { $self->resolve_prefetch( $_, $alias, $seen, $order, $collapse ) }
        @$pre;
  }
  elsif( ref $pre eq 'HASH' ) {
    my @ret =
    map {
      $self->resolve_prefetch($_, $alias, $seen, $order, $collapse),
      $self->related_source($_)->resolve_prefetch(
               $pre->{$_}, "${alias}.$_", $seen, $order, $collapse)
    } keys %$pre;
    #die Dumper \@ret;
    return @ret;
  }
  elsif( ref $pre ) {
    $self->throw_exception(
      "don't know how to resolve prefetch reftype ".ref($pre));
  }
  else {
    my $count = ++$seen->{$pre};
    my $as = ($count > 1 ? "${pre}_${count}" : $pre);
    my $rel_info = $self->relationship_info( $pre );
    $self->throw_exception( $self->name . " has no such relationship '$pre'" )
      unless $rel_info;
    my $as_prefix = ($alias =~ /^.*?\.(.+)$/ ? $1.'.' : '');
    my $rel_source = $self->related_source($pre);

    if (exists $rel_info->{attrs}{accessor}
         && $rel_info->{attrs}{accessor} eq 'multi') {
      $self->throw_exception(
        "Can't prefetch has_many ${pre} (join cond too complex)")
        unless ref($rel_info->{cond}) eq 'HASH';
      my $dots = @{[$as_prefix =~ m/\./g]} + 1; # +1 to match the ".${as_prefix}"
      if (my ($fail) = grep { @{[$_ =~ m/\./g]} == $dots }
                         keys %{$collapse}) {
        my ($last) = ($fail =~ /([^\.]+)$/);
        carp (
          "Prefetching multiple has_many rels ${last} and ${pre} "
          .(length($as_prefix)
            ? "at the same level (${as_prefix}) "
            : "at top level "
          )
          . 'will currently disrupt both the functionality of $rs->count(), '
          . 'and the amount of objects retrievable via $rs->next(). '
          . 'Use at your own risk.'
        );
      }
      #my @col = map { (/^self\.(.+)$/ ? ("${as_prefix}.$1") : ()); }
      #              values %{$rel_info->{cond}};
      $collapse->{".${as_prefix}${pre}"} = [ $rel_source->primary_columns ];
        # action at a distance. prepending the '.' allows simpler code
        # in ResultSet->_collapse_result
      my @key = map { (/^foreign\.(.+)$/ ? ($1) : ()); }
                    keys %{$rel_info->{cond}};
      my @ord = (ref($rel_info->{attrs}{order_by}) eq 'ARRAY'
                   ? @{$rel_info->{attrs}{order_by}}
                   : (defined $rel_info->{attrs}{order_by}
                       ? ($rel_info->{attrs}{order_by})
                       : ()));
      push(@$order, map { "${as}.$_" } (@key, @ord));
    }

    return map { [ "${as}.$_", "${as_prefix}${pre}.$_", ] }
      $rel_source->columns;
    #warn $alias, Dumper (\@ret);
    #return @ret;
  }
}

=head2 related_source

=over 4

=item Arguments: $relname

=item Return value: $source

=back

Returns the result source object for the given relationship.

=cut

sub related_source {
  my ($self, $rel) = @_;
  if( !$self->has_relationship( $rel ) ) {
    $self->throw_exception("No such relationship '$rel'");
  }
  return $self->schema->source($self->relationship_info($rel)->{source});
}

=head2 related_class

=over 4

=item Arguments: $relname

=item Return value: $classname

=back

Returns the class name for objects in the given relationship.

=cut

sub related_class {
  my ($self, $rel) = @_;
  if( !$self->has_relationship( $rel ) ) {
    $self->throw_exception("No such relationship '$rel'");
  }
  return $self->schema->class($self->relationship_info($rel)->{source});
}

=head2 handle

Obtain a new handle to this source. Returns an instance of a 
L<DBIx::Class::ResultSourceHandle>.

=cut

sub handle {
    return new DBIx::Class::ResultSourceHandle({
        schema         => $_[0]->schema,
        source_moniker => $_[0]->source_name
    });
}

=head2 throw_exception

See L<DBIx::Class::Schema/"throw_exception">.

=cut

sub throw_exception {
  my $self = shift;
  if (defined $self->schema) {
    $self->schema->throw_exception(@_);
  } else {
    croak(@_);
  }
}

=head2 source_info

Stores a hashref of per-source metadata.  No specific key names
have yet been standardized, the examples below are purely hypothetical
and don't actually accomplish anything on their own:

  __PACKAGE__->source_info({
    "_tablespace" => 'fast_disk_array_3',
    "_engine" => 'InnoDB',
  });

=head2 new

  $class->new();

  $class->new({attribute_name => value});

Creates a new ResultSource object.  Not normally called directly by end users.

=head2 column_info_from_storage

=over

=item Arguments: 1/0 (default: 0)

=item Return value: 1/0

=back

  __PACKAGE__->column_info_from_storage(1);

Enables the on-demand automatic loading of the above column
metadata from storage as neccesary.  This is *deprecated*, and
should not be used.  It will be removed before 1.0.


=head1 AUTHORS

Matt S. Trout <mst@shadowcatsystems.co.uk>

=head1 LICENSE

You may distribute this code under the same terms as Perl itself.

=cut

1;