use base qw/DBIx::Class/;
use DBIx::Class::Carp;
use DBIx::Class::ResultSetColumn;
-use Scalar::Util qw/blessed weaken/;
+use Scalar::Util qw/blessed weaken reftype/;
use Try::Tiny;
use Data::Compare (); # no imports!!! guard against insane architecture
'bool' => "_bool",
fallback => 1;
+# this is real - CDBICompat overrides it with insanity
+# yes, prototype won't matter, but that's for now ;)
+sub _bool () { 1 }
+
__PACKAGE__->mk_group_accessors('simple' => qw/_result_class result_source/);
=head1 NAME
=head3 Resolving conditions and attributes
-When a resultset is chained from another resultset, conditions and
-attributes with the same keys need resolving.
+When a resultset is chained from another resultset (ie:
+C<my $new_rs = $old_rs->search(\%extra_cond, \%attrs)>), conditions
+and attributes with the same keys need resolving.
+
+If any of L</columns>, L</select>, L</as> are present, they reset the
+original selection, and start the selection "clean".
-L</join>, L</prefetch>, L</+select>, L</+as> attributes are merged
-into the existing ones from the original resultset.
+The L</join>, L</prefetch>, L</+columns>, L</+select>, L</+as> attributes
+are merged into the existing ones from the original resultset.
The L</where> and L</having> attributes, and any search conditions, are
merged with an SQL C<AND> to the existing condition from the original
my $cache;
my %safe = (alias => 1, cache => 1);
if ( ! List::Util::first { !$safe{$_} } keys %$call_attrs and (
- ! defined $_[0]
+ ! defined $call_cond
or
- ref $_[0] eq 'HASH' && ! keys %{$_[0]}
+ ref $call_cond eq 'HASH' && ! keys %$call_cond
or
- ref $_[0] eq 'ARRAY' && ! @{$_[0]}
+ ref $call_cond eq 'ARRAY' && ! @$call_cond
)) {
$cache = $self->get_cache;
}
$attrs->{where}, $attrs
)];
return undef unless @$data;
- $self->{stashed_rows} = [ $data ];
- $self->_construct_objects->[0];
+ $self->{_stashed_rows} = [ $data ];
+ $self->_construct_results->[0];
}
return ($self->all)[0];
}
- return shift(@{$self->{stashed_objects}}) if @{ $self->{stashed_objects}||[] };
+ return shift(@{$self->{_stashed_results}}) if @{ $self->{_stashed_results}||[] };
- $self->{stashed_objects} = $self->_construct_objects
+ $self->{_stashed_results} = $self->_construct_results
or return undef;
- return shift @{$self->{stashed_objects}};
+ return shift @{$self->{_stashed_results}};
}
-# Constructs as many objects as it can in one pass while respecting
+# Constructs as many results as it can in one pass while respecting
# cursor laziness. Several modes of operation:
#
-# * Always builds everything present in @{$self->{stashed_rows}}
+# * Always builds everything present in @{$self->{_stashed_rows}}
# * If called with $fetch_all true - pulls everything off the cursor and
-# builds all objects in one pass
+# builds all result structures (or objects) in one pass
# * If $self->_resolved_attrs->{collapse} is true, checks the order_by
# and if the resultset is ordered properly by the left side:
# * Fetches stuff off the cursor until the "master object" changes,
-# and saves the last extra row (if any) in @{$self->{stashed_rows}}
+# and saves the last extra row (if any) in @{$self->{_stashed_rows}}
# OR
# * Just fetches, and collapses/constructs everything as if $fetch_all
# was requested (there is no other way to collapse except for an
# eager cursor)
# * If no collapse is requested - just get the next row, construct and
# return
-sub _construct_objects {
+sub _construct_results {
my ($self, $fetch_all) = @_;
my $rsrc = $self->result_source;
my $attrs = $self->_resolved_attrs;
- if (!$fetch_all and ! $attrs->{order_by} and $attrs->{collapse}) {
+ if (
+ ! $fetch_all
+ and
+ ! $attrs->{order_by}
+ and
+ $attrs->{collapse}
+ and
+ my @pcols = $rsrc->primary_columns
+ ) {
# default order for collapsing unless the user asked for something
- $attrs->{order_by} = [ map { join '.', $attrs->{alias}, $_} $rsrc->primary_columns ];
+ $attrs->{order_by} = [ map { join '.', $attrs->{alias}, $_} @pcols ];
$attrs->{_ordered_for_collapse} = 1;
$attrs->{_order_is_artificial} = 1;
}
my $cursor = $self->cursor;
# this will be used as both initial raw-row collector AND as a RV of
- # _construct_objects. Not regrowing the array twice matters a lot...
- # a suprising amount actually
- my $rows = (delete $self->{stashed_rows}) || [];
+ # _construct_results. Not regrowing the array twice matters a lot...
+ # a surprising amount actually
+ my $rows = delete $self->{_stashed_rows};
+
+ my $did_fetch_all = $fetch_all;
+
if ($fetch_all) {
# FIXME SUBOPTIMAL - we can do better, cursor->next/all (well diff. methods) should return a ref
- $rows = [ @$rows, $cursor->all ];
+ $rows = [ ($rows ? @$rows : ()), $cursor->all ];
}
- elsif (!$attrs->{collapse}) {
- # FIXME SUBOPTIMAL - we can do better, cursor->next/all (well diff. methods) should return a ref
- push @$rows, do { my @r = $cursor->next; @r ? \@r : () }
- unless @$rows;
- }
- else {
- $attrs->{_ordered_for_collapse} ||= (!$attrs->{order_by}) ? undef : do {
+ elsif( $attrs->{collapse} ) {
+
+ $attrs->{_ordered_for_collapse} = (!$attrs->{order_by}) ? 0 : do {
my $st = $rsrc->schema->storage;
my @ord_cols = map
{ $_->[0] }
{ $colinfos->{$_}{-colname} => $colinfos->{$_} }
@ord_cols
})) ? 1 : 0;
- };
+ } unless defined $attrs->{_ordered_for_collapse};
+
+ if (! $attrs->{_ordered_for_collapse}) {
+ $did_fetch_all = 1;
- if ($attrs->{_ordered_for_collapse}) {
- push @$rows, do { my @r = $cursor->next; @r ? \@r : () };
+ # instead of looping over ->next, use ->all in stealth mode
+ # *without* calling a ->reset afterwards
+ # FIXME ENCAPSULATION - encapsulation breach, cursor method additions pending
+ if (! $cursor->{_done}) {
+ $rows = [ ($rows ? @$rows : ()), $cursor->all ];
+ $cursor->{_done} = 1;
+ }
}
- # instead of looping over ->next, use ->all in stealth mode
- # *without* calling a ->reset afterwards
- # FIXME - encapsulation breach, got to be a better way
- elsif (! $cursor->{_done}) {
- push @$rows, $cursor->all;
- $cursor->{_done} = 1;
- $fetch_all = 1;
+ }
+
+ if (! $did_fetch_all and ! @{$rows||[]} ) {
+ # FIXME SUBOPTIMAL - we can do better, cursor->next/all (well diff. methods) should return a ref
+ if (scalar (my @r = $cursor->next) ) {
+ $rows = [ \@r ];
}
}
- return undef unless @$rows;
+ return undef unless @{$rows||[]};
- my $res_class = $self->result_class;
- my $inflator = $res_class->can ('inflate_result')
- or $self->throw_exception("Inflator $res_class does not provide an inflate_result() method");
+ my @extra_collapser_args;
+ if ($attrs->{collapse} and ! $did_fetch_all ) {
+
+ @extra_collapser_args = (
+ # FIXME SUBOPTIMAL - we can do better, cursor->next/all (well diff. methods) should return a ref
+ sub { my @r = $cursor->next or return; \@r }, # how the collapser gets more rows
+ ($self->{_stashed_rows} = []), # where does it stuff excess
+ );
+ }
+
+ # hotspot - skip the setter
+ my $res_class = $self->_result_class;
+
+ my $inflator_cref = $self->{_result_inflator}{cref} ||= do {
+ $res_class->can ('inflate_result')
+ or $self->throw_exception("Inflator $res_class does not provide an inflate_result() method");
+ };
my $infmap = $attrs->{as};
- if (!$attrs->{collapse} and $attrs->{_single_object_inflation}) {
- # construct a much simpler array->hash folder for the one-table cases right here
+ $self->{_result_inflator}{is_core_row} = ( (
+ $inflator_cref
+ ==
+ ( \&DBIx::Class::Row::inflate_result || die "No ::Row::inflate_result() - can't happen" )
+ ) ? 1 : 0 ) unless defined $self->{_result_inflator}{is_core_row};
+
+ $self->{_result_inflator}{is_hri} = ( (
+ ! $self->{_result_inflator}{is_core_row}
+ and
+ $inflator_cref == (
+ require DBIx::Class::ResultClass::HashRefInflator
+ &&
+ DBIx::Class::ResultClass::HashRefInflator->can('inflate_result')
+ )
+ ) ? 1 : 0 ) unless defined $self->{_result_inflator}{is_hri};
+
+
+ if (! $attrs->{_related_results_construction}) {
+ # construct a much simpler array->hash folder for the one-table cases right here
+ if ($self->{_result_inflator}{is_hri}) {
+ for my $r (@$rows) {
+ $r = { map { $infmap->[$_] => $r->[$_] } 0..$#$infmap };
+ }
+ }
# FIXME SUBOPTIMAL this is a very very very hot spot
# while rather optimal we can *still* do much better, by
- # building a smarter [Row|HRI]::inflate_result(), and
+ # building a smarter Row::inflate_result(), and
# switch to feeding it data via a much leaner interface
#
# crude unscientific benchmarking indicated the shortcut eval is not worth it for
# this particular resultset size
- if (@$rows < 60) {
- my @as_idx = 0..$#$infmap;
+ elsif (@$rows < 60) {
for my $r (@$rows) {
- $r = $inflator->($res_class, $rsrc, { map { $infmap->[$_] => $r->[$_] } @as_idx } );
+ $r = $inflator_cref->($res_class, $rsrc, { map { $infmap->[$_] => $r->[$_] } (0..$#$infmap) } );
}
}
else {
eval sprintf (
- '$_ = $inflator->($res_class, $rsrc, { %s }) for @$rows',
+ '$_ = $inflator_cref->($res_class, $rsrc, { %s }) for @$rows',
join (', ', map { "\$infmap->[$_] => \$_->[$_]" } 0..$#$infmap )
);
}
}
- else {
- $self->{_row_parser} ||= eval sprintf 'sub { %s }', $rsrc->_mk_row_parser({
+ # Special-case multi-object HRI (we always prune, and there is no $inflator_cref pass)
+ elsif ($self->{_result_inflator}{is_hri}) {
+ ( $self->{_row_parser}{hri} ||= $rsrc->_mk_row_parser({
+ eval => 1,
inflate_map => $infmap,
selection => $attrs->{select},
collapse => $attrs->{collapse},
premultiplied => $attrs->{_main_source_premultiplied},
- }) or die $@;
+ hri_style => 1,
+ prune_null_branches => 1,
+ }) )->($rows, @extra_collapser_args);
+ }
+ # Regular multi-object
+ else {
+ my $parser_type = $self->{_result_inflator}{is_core_row} ? 'classic_pruning' : 'classic_nonpruning';
- # modify $rows in-place, shrinking/extending as necessary
- $self->{_row_parser}->($rows, $fetch_all ? () : (
- # FIXME SUBOPTIMAL - we can do better, cursor->next/all (well diff. methods) should return a ref
- sub { my @r = $cursor->next or return; \@r }, # how the collapser gets more rows
- ($self->{stashed_rows} = []), # where does it stuff excess
- ));
+ ( $self->{_row_parser}{$parser_type} ||= $rsrc->_mk_row_parser({
+ eval => 1,
+ inflate_map => $infmap,
+ selection => $attrs->{select},
+ collapse => $attrs->{collapse},
+ premultiplied => $attrs->{_main_source_premultiplied},
+ prune_null_branches => $self->{_result_inflator}{is_core_row},
+ }) )->($rows, @extra_collapser_args);
- $_ = $inflator->($res_class, $rsrc, @$_) for @$rows;
+ $_ = $inflator_cref->($res_class, $rsrc, @$_) for @$rows;
}
- # CDBI compat stuff
- if ($attrs->{record_filter}) {
- $_ = $attrs->{record_filter}->($_) for @$rows;
- }
+ # The @$rows check seems odd at first - why wouldn't we want to warn
+ # regardless? The issue is things like find() etc, where the user
+ # *knows* only one result will come back. In these cases the ->all
+ # is not a pessimization, but rather something we actually want
+ carp_unique(
+ 'Unable to properly collapse has_many results in iterator mode due '
+ . 'to order criteria - performed an eager cursor slurp underneath. '
+ . 'Consider using ->all() instead'
+ ) if ( ! $fetch_all and @$rows > 1 );
return $rows;
}
sub result_class {
my ($self, $result_class) = @_;
if ($result_class) {
- unless (ref $result_class) { # don't fire this for an object
- $self->ensure_class_loaded($result_class);
+
+ # don't fire this for an object
+ $self->ensure_class_loaded($result_class)
+ unless ref($result_class);
+
+ if ($self->get_cache) {
+ carp_unique('Changing the result_class of a ResultSet instance with cached results is a noop - the cache contents will not be altered');
+ }
+ # FIXME ENCAPSULATION - encapsulation breach, cursor method additions pending
+ elsif ($self->{cursor} && $self->{cursor}{_pos}) {
+ $self->throw_exception('Changing the result_class of a ResultSet instance with an active cursor is not supported');
}
+
$self->_result_class($result_class);
- # THIS LINE WOULD BE A BUG - this accessor specifically exists to
- # permit the user to set result class on one result set only; it only
- # chains if provided to search()
- #$self->{attrs}{result_class} = $result_class if ref $self;
+
+ delete $self->{_result_inflator};
}
$self->_result_class;
}
my $tmp_attrs = { %$attrs };
# take off any limits, record_filter is cdbi, and no point of ordering nor locking a count
- delete @{$tmp_attrs}{qw/rows offset order_by record_filter for/};
+ delete @{$tmp_attrs}{qw/rows offset order_by _related_results_construction record_filter for/};
# overwrite the selector (supplied by the storage)
$tmp_attrs->{select} = $rsrc->storage->_count_select ($rsrc, $attrs);
my $sub_attrs = { %$attrs };
# extra selectors do not go in the subquery and there is no point of ordering it, nor locking it
- delete @{$sub_attrs}{qw/collapse columns as select _prefetch_selector_range order_by for/};
+ delete @{$sub_attrs}{qw/collapse columns as select _related_results_construction order_by for/};
# if we multi-prefetch we group_by something unique, as this is what we would
# get out of the rs via ->next/->all. We *DO WANT* to clobber old group_by regardless
->get_column ('count');
}
-sub _bool {
- return 1;
-}
=head2 count_literal
$self->throw_exception("all() doesn't take any arguments, you probably wanted ->search(...)->all()");
}
- delete @{$self}{qw/stashed_rows stashed_objects/};
+ delete @{$self}{qw/_stashed_rows _stashed_results/};
if (my $c = $self->get_cache) {
return @$c;
$self->cursor->reset;
- my $objs = $self->_construct_objects('fetch_all') || [];
+ my $objs = $self->_construct_results('fetch_all') || [];
$self->set_cache($objs) if $self->{attrs}{cache};
sub reset {
my ($self) = @_;
- delete @{$self}{qw/stashed_rows stashed_objects/};
+ delete @{$self}{qw/_stashed_rows _stashed_results/};
$self->{all_cache_position} = 0;
$self->cursor->reset;
return $self;
my $attrs = { %{$self->_resolved_attrs} };
my $join_classifications;
- my $existing_group_by = delete $attrs->{group_by};
+ my ($existing_group_by) = delete @{$attrs}{qw(group_by _grouped_by_distinct)};
# do we need a subquery for any reason?
my $needs_subq = (
);
# make a new $rs selecting only the PKs (that's all we really need for the subq)
- delete $attrs->{$_} for qw/collapse select _prefetch_selector_range as/;
+ delete $attrs->{$_} for qw/select as collapse _related_results_construction/;
$attrs->{columns} = [ map { "$attrs->{alias}.$_" } @$idcols ];
$attrs->{group_by} = \ ''; # FIXME - this is an evil hack, it causes the optimiser to kick in and throw away the LEFT joins
my $subrs = (ref $self)->new($rsrc, $attrs);
my ($merged_cond, $cols_from_relations) = $self->_merge_with_rscond($values);
- my %new = (
+ my $new = $self->result_class->new({
%$merged_cond,
- @$cols_from_relations
+ ( @$cols_from_relations
? (-cols_from_relations => $cols_from_relations)
- : (),
+ : ()
+ ),
-result_source => $self->result_source, # DO NOT REMOVE THIS, REQUIRED
- );
+ });
- return $self->result_class->new(\%new);
+ if (
+ reftype($new) eq 'HASH'
+ and
+ ! keys %$new
+ and
+ blessed($new)
+ ) {
+ carp_unique (sprintf (
+ "%s->new returned a blessed empty hashref - a strong indicator something is wrong with its inheritance chain",
+ $self->result_class,
+ ));
+ }
+
+ $new;
}
# _merge_with_rscond
sub related_resultset {
my ($self, $rel) = @_;
- $self->{related_resultsets} ||= {};
return $self->{related_resultsets}{$rel} ||= do {
my $rsrc = $self->result_source;
my $rel_info = $rsrc->relationship_info($rel);
#XXX - temp fix for result_class bug. There likely is a more elegant fix -groditi
delete @{$attrs}{qw(result_class alias)};
- my $new_cache;
+ my $related_cache;
if (my $cache = $self->get_cache) {
- if ($cache->[0] && $cache->[0]->related_resultset($rel)->get_cache) {
- $new_cache = [ map { @{$_->related_resultset($rel)->get_cache||[]} }
- @$cache ];
- }
+ $related_cache = [ map
+ { @{$_->related_resultset($rel)->get_cache||[]} }
+ @$cache
+ ];
}
my $rel_source = $rsrc->related_source($rel);
where => $attrs->{where},
});
};
- $new->set_cache($new_cache) if $new_cache;
+ $new->set_cache($related_cache) if $related_cache;
$new;
};
}
# ->_resolve_join as otherwise they get lost - captainL
my $join = $self->_merge_joinpref_attr( $attrs->{join}, $attrs->{prefetch} );
- delete @{$attrs}{qw/join prefetch collapse group_by distinct select as columns +select +as +columns/};
+ delete @{$attrs}{qw/join prefetch collapse group_by distinct _grouped_by_distinct select as columns +select +as +columns/};
my $seen = { %{ (delete $attrs->{seen_join}) || {} } };
return {%$attrs, from => $from, seen_join => $seen};
}
-# FIXME - this needs to go live in Schema with the tree walker... or
-# something
-my $inflatemap_checker;
-$inflatemap_checker = sub {
- my ($rsrc, $relpaths) = @_;
-
- my $rels;
-
- for (@$relpaths) {
- $_ =~ /^ ( [^\.]+ ) \. (.+) $/x
- or next;
-
- push @{$rels->{$1}}, $2;
- }
-
- for my $rel (keys %$rels) {
- my $rel_rsrc = try {
- $rsrc->related_source ($rel)
- } catch {
- $rsrc->throw_exception(sprintf(
- "Inflation into non-existent relationship '%s' of '%s' requested, "
- . "check the inflation specification (columns/as) ending in '...%s.%s'",
- $rel,
- $rsrc->source_name,
- $rel,
- ( sort { length($a) <=> length ($b) } @{$rels->{$rel}} )[0],
- ))};
-
- $inflatemap_checker->($rel_rsrc, $rels->{$rel});
- }
-
- return;
-};
-
sub _resolved_attrs {
my $self = shift;
return $self->{_attrs} if $self->{_attrs};
}
}
- # validate the user-supplied 'as' chain
- # folks get too confused by the (logical) exception message, need to
- # go to some lengths to clarify the text
- #
- # FIXME - this needs to go live in Schema with the tree walker... or
- # something
- $inflatemap_checker->($source, \@as);
-
$attrs->{select} = \@sel;
$attrs->{as} = \@as;
carp_unique ("Useless use of distinct on a grouped resultset ('distinct' is ignored when a 'group_by' is present)");
}
else {
+ $attrs->{_grouped_by_distinct} = 1;
# distinct affects only the main selection part, not what prefetch may
# add below.
$attrs->{group_by} = $source->storage->_group_over_selection (
my @prefetch = $source->_resolve_prefetch( $prefetch, $alias, $join_map );
- # we need to somehow mark which columns came from prefetch
- if (@prefetch) {
- my $sel_end = $#{$attrs->{select}};
- $attrs->{_prefetch_selector_range} = [ $sel_end + 1, $sel_end + @prefetch ];
- }
-
push @{ $attrs->{select} }, (map { $_->[0] } @prefetch);
push @{ $attrs->{as} }, (map { $_->[1] } @prefetch);
}
- if ( ! List::Util::first { $_ =~ /\./ } @{$attrs->{as}} ) {
- $attrs->{_single_object_inflation} = 1;
+ if ( List::Util::first { $_ =~ /\./ } @{$attrs->{as}} ) {
+ $attrs->{_related_results_construction} = 1;
+ }
+ else {
$attrs->{collapse} = 0;
}
# A cursor in progress can't be serialized (and would make little sense anyway)
# the parser can be regenerated (and can't be serialized)
- delete @{$to_serialize}{qw/cursor _row_parser/};
+ delete @{$to_serialize}{qw/cursor _row_parser _result_inflator/};
# nor is it sensical to store a not-yet-fired-count pager
if ($to_serialize->{pager} and ref $to_serialize->{pager}{total_entries} eq 'CODE') {
}
}
+1;
+
+__END__
+
# XXX: FIXME: Attributes docs need clearing up
=head1 ATTRIBUTES
=over 4
-=item Value: \@columns
+=item Value: \@columns | \%columns | $column
=back
=back
-=head2 +as
-
-=over 4
-
-Indicates additional column names for those added via L</+select>. See L</as>.
-
-=back
-
=head2 as
=over 4
You can create your own accessors if required - see
L<DBIx::Class::Manual::Cookbook> for details.
+=head2 +as
+
+=over 4
+
+Indicates additional column names for those added via L</+select>. See L</as>.
+
+=back
+
=head2 join
=over 4
will return a set of all artists that have both a cd with title 'Down
to Earth' and a cd with title 'Popular'.
-If you want to fetch related objects from other tables as well, see C<prefetch>
+If you want to fetch related objects from other tables as well, see L</prefetch>
below.
NOTE: An internal join-chain pruner will discard certain joins while
For more help on using joins with search, see L<DBIx::Class::Manual::Joining>.
-=head2 prefetch
+=head2 collapse
=over 4
-=item Value: ($rel_name | \@rel_names | \%rel_names)
+=item Value: (0 | 1)
=back
-Contains one or more relationships that should be fetched along with
-the main query (when they are accessed afterwards the data will
-already be available, without extra queries to the database). This is
-useful for when you know you will need the related objects, because it
-saves at least one query:
-
- my $rs = $schema->resultset('Tag')->search(
- undef,
- {
- prefetch => {
- cd => 'artist'
- }
- }
- );
-
-The initial search results in SQL like the following:
-
- SELECT tag.*, cd.*, artist.* FROM tag
- JOIN cd ON tag.cd = cd.cdid
- JOIN artist ON cd.artist = artist.artistid
-
-L<DBIx::Class> has no need to go back to the database when we access the
-C<cd> or C<artist> relationships, which saves us two SQL statements in this
-case.
-
-Simple prefetches will be joined automatically, so there is no need
-for a C<join> attribute in the above search.
-
-L</prefetch> can be used with the any of the relationship types and
-multiple prefetches can be specified together. Below is a more complex
-example that prefetches a CD's artist, its liner notes (if present),
-the cover image, the tracks on that cd, and the guests on those
-tracks.
-
- # Assuming:
- My::Schema::CD->belongs_to( artist => 'My::Schema::Artist' );
- My::Schema::CD->might_have( liner_note => 'My::Schema::LinerNotes' );
- My::Schema::CD->has_one( cover_image => 'My::Schema::Artwork' );
- My::Schema::CD->has_many( tracks => 'My::Schema::Track' );
-
- My::Schema::Artist->belongs_to( record_label => 'My::Schema::RecordLabel' );
-
- My::Schema::Track->has_many( guests => 'My::Schema::Guest' );
+When set to a true value, indicates that any rows fetched from joined has_many
+relationships are to be aggregated into the corresponding "parent" object. For
+example, the resultset:
+ my $rs = $schema->resultset('CD')->search({}, {
+ '+columns' => [ qw/ tracks.title tracks.position / ],
+ join => 'tracks',
+ collapse => 1,
+ });
- my $rs = $schema->resultset('CD')->search(
- undef,
- {
- prefetch => [
- { artist => 'record_label'}, # belongs_to => belongs_to
- 'liner_note', # might_have
- 'cover_image', # has_one
- { tracks => 'guests' }, # has_many => has_many
- ]
- }
- );
-
-This will produce SQL like the following:
-
- SELECT cd.*, artist.*, record_label.*, liner_note.*, cover_image.*,
- tracks.*, guests.*
- FROM cd me
- JOIN artist artist
- ON artist.artistid = me.artistid
- JOIN record_label record_label
- ON record_label.labelid = artist.labelid
- LEFT JOIN track tracks
- ON tracks.cdid = me.cdid
- LEFT JOIN guest guests
- ON guests.trackid = track.trackid
- LEFT JOIN liner_notes liner_note
- ON liner_note.cdid = me.cdid
- JOIN cd_artwork cover_image
- ON cover_image.cdid = me.cdid
- ORDER BY tracks.cd
-
-Now the C<artist>, C<record_label>, C<liner_note>, C<cover_image>,
-C<tracks>, and C<guests> of the CD will all be available through the
-relationship accessors without the need for additional queries to the
-database.
-
-However, there is one caveat to be observed: it can be dangerous to
-prefetch more than one L<has_many|DBIx::Class::Relationship/has_many>
-relationship on a given level. e.g.:
-
- my $rs = $schema->resultset('CD')->search(
- undef,
- {
- prefetch => [
- 'tracks', # has_many
- { cd_to_producer => 'producer' }, # has_many => belongs_to (i.e. m2m)
- ]
- }
- );
-
-The collapser currently can't identify duplicate tuples for multiple
-L<has_many|DBIx::Class::Relationship/has_many> relationships and as a
-result the second L<has_many|DBIx::Class::Relationship/has_many>
-relation could contain redundant objects.
-
-=head3 Using L</prefetch> with L</join>
-
-L</prefetch> implies a L</join> with the equivalent argument, and is
-properly merged with any existing L</join> specification. So the
-following:
-
- my $rs = $schema->resultset('CD')->search(
- {'record_label.name' => 'Music Product Ltd.'},
- {
- join => {artist => 'record_label'},
- prefetch => 'artist',
- }
- );
+While executing the following query:
-... will work, searching on the record label's name, but only
-prefetching the C<artist>.
+ SELECT me.*, tracks.title, tracks.position
+ FROM cd me
+ LEFT JOIN track tracks
+ ON tracks.cdid = me.cdid
-=head3 Using L</prefetch> with L</select> / L</+select> / L</as> / L</+as>
+Will return only as many objects as there are rows in the CD source, even
+though the result of the query may span many rows. Each of these CD objects
+will in turn have multiple "Track" objects hidden behind the has_many
+generated accessor C<tracks>. Without C<< collapse => 1 >>, the return values
+of this resultset would be as many CD objects as there are tracks (a "Cartesian
+product"), with each CD object containing exactly one of all fetched Track data.
-L</prefetch> implies a L</+select>/L</+as> with the fields of the
-prefetched relations. So given:
+When a collapse is requested on a non-ordered resultset, an order by some
+unique part of the main source (the left-most table) is inserted automatically.
+This is done so that the resultset is allowed to be "lazy" - calling
+L<< $rs->next|/next >> will fetch only as many rows as it needs to build the next
+object with all of its related data.
- my $rs = $schema->resultset('CD')->search(
- undef,
- {
- select => ['cd.title'],
- as => ['cd_title'],
- prefetch => 'artist',
- }
- );
+If an L</order_by> is already declared, and orders the resultset in a way that
+makes collapsing as described above impossible (e.g. C<< ORDER BY
+has_many_rel.column >> or C<ORDER BY RANDOM()>), DBIC will automatically
+switch to "eager" mode and slurp the entire resultset before consturcting the
+first object returned by L</next>.
-The L</select> becomes: C<'cd.title', 'artist.*'> and the L</as>
-becomes: C<'cd_title', 'artist.*'>.
+Setting this attribute on a resultset that does not join any has_many
+relations is a no-op.
-=head3 CAVEATS
+For a more in-depth discussion, see L</PREFETCHING>.
-Prefetch does a lot of deep magic. As such, it may not behave exactly
-as you might expect.
+=head2 prefetch
=over 4
-=item *
-
-Prefetch uses the L</cache> to populate the prefetched relationships. This
-may or may not be what you want.
+=item Value: ($rel_name | \@rel_names | \%rel_names)
-=item *
+=back
-If you specify a condition on a prefetched relationship, ONLY those
-rows that match the prefetched condition will be fetched into that relationship.
-This means that adding prefetch to a search() B<may alter> what is returned by
-traversing a relationship. So, if you have C<< Artist->has_many(CDs) >> and you do
+This attribute is a shorthand for specifying a L</join> spec, adding all
+columns from the joined related sources as L</+columns> and setting
+L</collapse> to a true value. For example, the following two queries are
+equivalent:
- my $artist_rs = $schema->resultset('Artist')->search({
- 'cds.year' => 2008,
- }, {
- join => 'cds',
+ my $rs = $schema->resultset('Artist')->search({}, {
+ prefetch => { cds => ['genre', 'tracks' ] },
});
- my $count = $artist_rs->first->cds->count;
+and
- my $artist_rs_prefetch = $artist_rs->search( {}, { prefetch => 'cds' } );
+ my $rs = $schema->resultset('Artist')->search({}, {
+ join => { cds => ['genre', 'tracks' ] },
+ collapse => 1,
+ '+columns' => [
+ (map
+ { +{ "cds.$_" => "cds.$_" } }
+ $schema->source('Artist')->related_source('cds')->columns
+ ),
+ (map
+ { +{ "cds.genre.$_" => "genre.$_" } }
+ $schema->source('Artist')->related_source('cds')->related_source('genre')->columns
+ ),
+ (map
+ { +{ "cds.tracks.$_" => "tracks.$_" } }
+ $schema->source('Artist')->related_source('cds')->related_source('tracks')->columns
+ ),
+ ],
+ });
- my $prefetch_count = $artist_rs_prefetch->first->cds->count;
+Both producing the following SQL:
+
+ SELECT me.artistid, me.name, me.rank, me.charfield,
+ cds.cdid, cds.artist, cds.title, cds.year, cds.genreid, cds.single_track,
+ genre.genreid, genre.name,
+ tracks.trackid, tracks.cd, tracks.position, tracks.title, tracks.last_updated_on, tracks.last_updated_at
+ FROM artist me
+ LEFT JOIN cd cds
+ ON cds.artist = me.artistid
+ LEFT JOIN genre genre
+ ON genre.genreid = cds.genreid
+ LEFT JOIN track tracks
+ ON tracks.cd = cds.cdid
+ ORDER BY me.artistid
+
+While L</prefetch> implies a L</join>, it is ok to mix the two together, as
+the arguments are properly merged and generally do the right thing. For
+example, you may want to do the following:
+
+ my $artists_and_cds_without_genre = $schema->resultset('Artist')->search(
+ { 'genre.genreid' => undef },
+ {
+ join => { cds => 'genre' },
+ prefetch => 'cds',
+ }
+ );
- cmp_ok( $count, '==', $prefetch_count, "Counts should be the same" );
+Which generates the following SQL:
-that cmp_ok() may or may not pass depending on the datasets involved. This
-behavior may or may not survive the 0.09 transition.
+ SELECT me.artistid, me.name, me.rank, me.charfield,
+ cds.cdid, cds.artist, cds.title, cds.year, cds.genreid, cds.single_track
+ FROM artist me
+ LEFT JOIN cd cds
+ ON cds.artist = me.artistid
+ LEFT JOIN genre genre
+ ON genre.genreid = cds.genreid
+ WHERE genre.genreid IS NULL
+ ORDER BY me.artistid
-=back
+For a more in-depth discussion, see L</PREFETCHING>.
=head2 alias
... FOR SHARED. If \$scalar is passed, this is taken directly and embedded in the
query.
+=head1 PREFETCHING
+
+DBIx::Class supports arbitrary related data prefetching from multiple related
+sources. Any combination of relationship types and column sets are supported.
+If L<collapsing|/collapse> is requested, there is an additional requirement of
+selecting enough data to make every individual object uniquely identifiable.
+
+Here are some more involved examples, based on the following relationship map:
+
+ # Assuming:
+ My::Schema::CD->belongs_to( artist => 'My::Schema::Artist' );
+ My::Schema::CD->might_have( liner_note => 'My::Schema::LinerNotes' );
+ My::Schema::CD->has_many( tracks => 'My::Schema::Track' );
+
+ My::Schema::Artist->belongs_to( record_label => 'My::Schema::RecordLabel' );
+
+ My::Schema::Track->has_many( guests => 'My::Schema::Guest' );
+
+
+
+ my $rs = $schema->resultset('Tag')->search(
+ undef,
+ {
+ prefetch => {
+ cd => 'artist'
+ }
+ }
+ );
+
+The initial search results in SQL like the following:
+
+ SELECT tag.*, cd.*, artist.* FROM tag
+ JOIN cd ON tag.cd = cd.cdid
+ JOIN artist ON cd.artist = artist.artistid
+
+L<DBIx::Class> has no need to go back to the database when we access the
+C<cd> or C<artist> relationships, which saves us two SQL statements in this
+case.
+
+Simple prefetches will be joined automatically, so there is no need
+for a C<join> attribute in the above search.
+
+The L</prefetch> attribute can be used with any of the relationship types
+and multiple prefetches can be specified together. Below is a more complex
+example that prefetches a CD's artist, its liner notes (if present),
+the cover image, the tracks on that CD, and the guests on those
+tracks.
+
+ my $rs = $schema->resultset('CD')->search(
+ undef,
+ {
+ prefetch => [
+ { artist => 'record_label'}, # belongs_to => belongs_to
+ 'liner_note', # might_have
+ 'cover_image', # has_one
+ { tracks => 'guests' }, # has_many => has_many
+ ]
+ }
+ );
+
+This will produce SQL like the following:
+
+ SELECT cd.*, artist.*, record_label.*, liner_note.*, cover_image.*,
+ tracks.*, guests.*
+ FROM cd me
+ JOIN artist artist
+ ON artist.artistid = me.artistid
+ JOIN record_label record_label
+ ON record_label.labelid = artist.labelid
+ LEFT JOIN track tracks
+ ON tracks.cdid = me.cdid
+ LEFT JOIN guest guests
+ ON guests.trackid = track.trackid
+ LEFT JOIN liner_notes liner_note
+ ON liner_note.cdid = me.cdid
+ JOIN cd_artwork cover_image
+ ON cover_image.cdid = me.cdid
+ ORDER BY tracks.cd
+
+Now the C<artist>, C<record_label>, C<liner_note>, C<cover_image>,
+C<tracks>, and C<guests> of the CD will all be available through the
+relationship accessors without the need for additional queries to the
+database.
+
+=head3 CAVEATS
+
+Prefetch does a lot of deep magic. As such, it may not behave exactly
+as you might expect.
+
+=over 4
+
+=item *
+
+Prefetch uses the L</cache> to populate the prefetched relationships. This
+may or may not be what you want.
+
+=item *
+
+If you specify a condition on a prefetched relationship, ONLY those
+rows that match the prefetched condition will be fetched into that relationship.
+This means that adding prefetch to a search() B<may alter> what is returned by
+traversing a relationship. So, if you have C<< Artist->has_many(CDs) >> and you do
+
+ my $artist_rs = $schema->resultset('Artist')->search({
+ 'cds.year' => 2008,
+ }, {
+ join => 'cds',
+ });
+
+ my $count = $artist_rs->first->cds->count;
+
+ my $artist_rs_prefetch = $artist_rs->search( {}, { prefetch => 'cds' } );
+
+ my $prefetch_count = $artist_rs_prefetch->first->cds->count;
+
+ cmp_ok( $count, '==', $prefetch_count, "Counts should be the same" );
+
+That cmp_ok() may or may not pass depending on the datasets involved. In other
+words the C<WHERE> condition would apply to the entire dataset, just like
+it would in regular SQL. If you want to add a condition only to the "right side"
+of a C<LEFT JOIN> - consider declaring and using a L<relationship with a custom
+condition|DBIx::Class::Relationship::Base/condition>
+
+=back
+
=head1 DBIC BIND VALUES
Because DBIC may need more information to bind values than just the column name
You may distribute this code under the same terms as Perl itself.
-=cut
-
-1;
projects / dbsrgits/DBIx-Class.git / blobdiff