NAME

DBIx::Class::ResultSet - Responsible for fetching and creating resultset.

SYNOPSIS

my $rs   = $schema->resultset('User')->search({ registered => 1 });
my @rows = $schema->resultset('CD')->search({ year => 2005 })->all();

DESCRIPTION

The resultset is also known as an iterator. It is responsible for handling queries that may return an arbitrary number of rows, e.g. via "search" or a has_many relationship.

In the examples below, the following table classes are used:

package MyApp::Schema::Artist;
use base qw/DBIx::Class/;
__PACKAGE__->load_components(qw/Core/);
__PACKAGE__->table('artist');
__PACKAGE__->add_columns(qw/artistid name/);
__PACKAGE__->set_primary_key('artistid');
__PACKAGE__->has_many(cds => 'MyApp::Schema::CD');
1;

package MyApp::Schema::CD;
use base qw/DBIx::Class/;
__PACKAGE__->load_components(qw/Core/);
__PACKAGE__->table('cd');
__PACKAGE__->add_columns(qw/cdid artist title year/);
__PACKAGE__->set_primary_key('cdid');
__PACKAGE__->belongs_to(artist => 'MyApp::Schema::Artist');
1;

OVERLOADING

If a resultset is used in a numeric context it returns the "count". However, if it is used in a booleand context it is always true. So if you want to check if a resultset has any results use if $rs != 0. if $rs will always be true.

METHODS

new

Arguments: $source, \%$attrs
Return Value: $rs

The resultset constructor. Takes a source object (usually a DBIx::Class::ResultSourceProxy::Table) and an attribute hash (see "ATTRIBUTES" below). Does not perform any queries -- these are executed as needed by the other methods.

Generally you won't need to construct a resultset manually. You'll automatically get one from e.g. a "search" called in scalar context:

my $rs = $schema->resultset('CD')->search({ title => '100th Window' });

IMPORTANT: If called on an object, proxies to new_result instead so

my $cd = $schema->resultset('CD')->new({ title => 'Spoon' });

will return a CD object, not a ResultSet.

search

Arguments: $cond, \%attrs?
Return Value: $resultset (scalar context), @row_objs (list context)

my @cds    = $cd_rs->search({ year => 2001 }); # "... WHERE year = 2001"
my $new_rs = $cd_rs->search({ year => 2005 });

my $new_rs = $cd_rs->search([ { year => 2005 }, { year => 2004 } ]);
               # year = 2005 OR year = 2004

If you need to pass in additional attributes but no additional condition, call it as search(undef, \%attrs).

# "SELECT name, artistid FROM $artist_table"
my @all_artists = $schema->resultset('Artist')->search(undef, {
  columns => [qw/name artistid/],
});

For a list of attributes that can be passed to search, see "ATTRIBUTES". For more examples of using this function, see Searching. For a complete documentation for the first argument, see SQL::Abstract.

For more help on using joins with search, see DBIx::Class::Manual::Joining.

search_rs

Arguments: $cond, \%attrs?
Return Value: $resultset

This method does the same exact thing as search() except it will always return a resultset, even in list context.

search_literal

Arguments: $sql_fragment, @bind_values
Return Value: $resultset (scalar context), @row_objs (list context)

my @cds   = $cd_rs->search_literal('year = ? AND title = ?', qw/2001 Reload/);
my $newrs = $artist_rs->search_literal('name = ?', 'Metallica');

Pass a literal chunk of SQL to be added to the conditional part of the resultset query.

CAVEAT: search_literal is provided for Class::DBI compatibility and should only be used in that context. There are known problems using search_literal in chained queries; it can result in bind values in the wrong order. See "Searching" in DBIx::Class::Manual::Cookbook and "Searching" in DBIx::Class::Manual::FAQ for searching techniques that do not require search_literal.

find

Arguments: @values | \%cols, \%attrs?
Return Value: $row_object | undef

Finds a row based on its primary key or unique constraint. For example, to find a row by its primary key:

my $cd = $schema->resultset('CD')->find(5);

You can also find a row by a specific unique constraint using the key attribute. For example:

my $cd = $schema->resultset('CD')->find('Massive Attack', 'Mezzanine', {
  key => 'cd_artist_title'
});

Additionally, you can specify the columns explicitly by name:

my $cd = $schema->resultset('CD')->find(
  {
    artist => 'Massive Attack',
    title  => 'Mezzanine',
  },
  { key => 'cd_artist_title' }
);

If the key is specified as primary, it searches only on the primary key.

If no key is specified, it searches on all unique constraints defined on the source for which column data is provided, including the primary key.

If your table does not have a primary key, you must provide a value for the key attribute matching one of the unique constraints on the source.

Note: If your query does not return only one row, a warning is generated:

Query returned more than one row

See also "find_or_create" and "update_or_create". For information on how to declare unique constraints, see "add_unique_constraint" in DBIx::Class::ResultSource.

search_related

Arguments: $rel, $cond, \%attrs?
Return Value: $new_resultset

$new_rs = $cd_rs->search_related('artist', {
  name => 'Emo-R-Us',
});

Searches the specified relationship, optionally specifying a condition and attributes for matching records. See "ATTRIBUTES" for more information.

search_related_rs

This method works exactly the same as search_related, except that it guarantees a restultset, even in list context.

cursor

Arguments: none
Return Value: $cursor

Returns a storage-driven cursor to the given resultset. See DBIx::Class::Cursor for more information.

single

Arguments: $cond?
Return Value: $row_object?

my $cd = $schema->resultset('CD')->single({ year => 2001 });

Inflates the first result without creating a cursor if the resultset has any records in it; if not returns nothing. Used by "find" as a lean version of "search".

While this method can take an optional search condition (just like "search") being a fast-code-path it does not recognize search attributes. If you need to add extra joins or similar, call "search" and then chain-call "single" on the DBIx::Class::ResultSet returned.

Note

As of 0.08100, this method enforces the assumption that the preceeding query returns only one row. If more than one row is returned, you will receive a warning:

Query returned more than one row

In this case, you should be using "first" or "find" instead, or if you really know what you are doing, use the "rows" attribute to explicitly limit the size of the resultset.

get_column

Arguments: $cond?
Return Value: $resultsetcolumn

my $max_length = $rs->get_column('length')->max;

Returns a DBIx::Class::ResultSetColumn instance for a column of the ResultSet.

search_like

Arguments: $cond, \%attrs?
Return Value: $resultset (scalar context), @row_objs (list context)

# WHERE title LIKE '%blue%'
$cd_rs = $rs->search_like({ title => '%blue%'});

Performs a search, but uses LIKE instead of = as the condition. Note that this is simply a convenience method. You most likely want to use "search" with specific operators.

For more information, see DBIx::Class::Manual::Cookbook.

slice

Arguments: $first, $last
Return Value: $resultset (scalar context), @row_objs (list context)

Returns a resultset or object list representing a subset of elements from the resultset slice is called on. Indexes are from 0, i.e., to get the first three records, call:

my ($one, $two, $three) = $rs->slice(0, 2);

Arguments: none
Return Value: $result?

Returns the next element in the resultset (undef is there is none).

Can be used to efficiently iterate over records in the resultset:

my $rs = $schema->resultset('CD')->search;
while (my $cd = $rs->next) {
  print $cd->title;
}

Note that you need to store the resultset object, and call next on it. Calling resultset('Table')->next repeatedly will always return the first record from the resultset.

result_source

Arguments: $result_source?
Return Value: $result_source

An accessor for the primary ResultSource object from which this ResultSet is derived.

result_class

Arguments: $result_class?
Return Value: $result_class

An accessor for the class to use when creating row objects. Defaults to result_source->result_class - which in most cases is the name of the "table" class.

count

Arguments: $cond, \%attrs??
Return Value: $count

Performs an SQL COUNT with the same query as the resultset was built with to find the number of elements. If passed arguments, does a search on the resultset and counts the results of that.

Note: When using count with group_by, DBIx::Class emulates GROUP BY using COUNT( DISTINCT( columns ) ). Some databases (notably SQLite) do not support DISTINCT with multiple columns. If you are using such a database, you should only use columns from the main table in your group_by clause.

count_literal

Arguments: $sql_fragment, @bind_values
Return Value: $count

Counts the results in a literal query. Equivalent to calling "search_literal" with the passed arguments, then "count".

all

Arguments: none
Return Value: @objects

Returns all elements in the resultset. Called implicitly if the resultset is returned in list context.

reset

Arguments: none
Return Value: $self

Resets the resultset's cursor, so you can iterate through the elements again.

first

Arguments: none
Return Value: $object?

Resets the resultset and returns an object for the first result (if the resultset returns anything).

update

Arguments: \%values
Return Value: $storage_rv

Sets the specified columns in the resultset to the supplied values in a single query. Return value will be true if the update succeeded or false if no records were updated; exact type of success value is storage-dependent.

update_all

Arguments: \%values
Return Value: 1

Fetches all objects and updates them one at a time. Note that update_all will run DBIC cascade triggers, while "update" will not.

delete

Arguments: none
Return Value: 1

Deletes the contents of the resultset from its result source. Note that this will not run DBIC cascade triggers. See "delete_all" if you need triggers to run. See also "delete" in DBIx::Class::Row.

delete may not generate correct SQL for a query with joins or a resultset chained from a related resultset. In this case it will generate a warning:-

WARNING! Currently $rs->delete() does not generate proper SQL on
joined resultsets, and may delete rows well outside of the contents
of $rs. Use at your own risk

In these cases you may find that delete_all is more appropriate, or you need to respecify your query in a way that can be expressed without a join.

delete_all

Arguments: none
Return Value: 1

Fetches all objects and deletes them one at a time. Note that delete_all will run DBIC cascade triggers, while "delete" will not.

populate

Arguments: \@data;

Pass an arrayref of hashrefs. Each hashref should be a structure suitable for submitting to a $resultset->create(...) method.

In void context, insert_bulk in DBIx::Class::Storage::DBI is used to insert the data, as this is a faster method.

Otherwise, each set of data is inserted into the database using "create" in DBIx::Class::ResultSet, and a arrayref of the resulting row objects is returned.

Example: Assuming an Artist Class that has many CDs Classes relating:

my $Artist_rs = $schema->resultset("Artist");

## Void Context Example 
$Artist_rs->populate([
   { artistid => 4, name => 'Manufactured Crap', cds => [ 
      { title => 'My First CD', year => 2006 },
      { title => 'Yet More Tweeny-Pop crap', year => 2007 },
    ],
   },
   { artistid => 5, name => 'Angsty-Whiny Girl', cds => [
      { title => 'My parents sold me to a record company' ,year => 2005 },
      { title => 'Why Am I So Ugly?', year => 2006 },
      { title => 'I Got Surgery and am now Popular', year => 2007 }
    ],
   },
]);

## Array Context Example
my ($ArtistOne, $ArtistTwo, $ArtistThree) = $Artist_rs->populate([
  { name => "Artist One"},
  { name => "Artist Two"},
  { name => "Artist Three", cds=> [
  { title => "First CD", year => 2007},
  { title => "Second CD", year => 2008},
]}
]);

print $ArtistOne->name; ## response is 'Artist One'
print $ArtistThree->cds->count ## reponse is '2'

Please note an important effect on your data when choosing between void and wantarray context. Since void context goes straight to insert_bulk in DBIx::Class::Storage::DBI this will skip any component that is overriding c<insert>. So if you are using something like DBIx-Class-UUIDColumns to create primary keys for you, you will find that your PKs are empty. In this case you will have to use the wantarray context in order to create those values.

Arguments: none
Return Value: $pager

Return Value a Data::Page object for the current resultset. Only makes sense for queries with a page attribute.

new_result

Arguments: \%vals
Return Value: $rowobject

Creates a new row object in the resultset's result class and returns it. The row is not inserted into the database at this point, call "insert" in DBIx::Class::Row to do that. Calling "in_storage" in DBIx::Class::Row will tell you whether the row object has been inserted or not.

Passes the hashref of input on to "new" in DBIx::Class::Row.

find_or_new

Arguments: \%vals, \%attrs?
Return Value: $rowobject

my $artist = $schema->resultset('Artist')->find_or_new(
  { artist => 'fred' }, { key => 'artists' });

$cd->cd_to_producer->find_or_new({ producer => $producer },
                                 { key => 'primary });

Find an existing record from this resultset, based on it's primary key, or a unique constraint. If none exists, instantiate a new result object and return it. The object will not be saved into your storage until you call "insert" in DBIx::Class::Row on it.

You most likely want this method when looking for existing rows using a unique constraint that is not the primary key, or looking for related rows.

If you want objects to be saved immediately, use "find_or_create" instead.

Note: find_or_new is probably not what you want when creating a new row in a table that uses primary keys supplied by the database. Passing in a primary key column with a value of undef will cause "find" to attempt to search for a row with a value of NULL.

create

Arguments: \%vals
Return Value: a DBIx::Class::Row $object

Attempt to create a single new row or a row with multiple related rows in the table represented by the resultset (and related tables). This will not check for duplicate rows before inserting, use "find_or_create" to do that.

To create one row for this resultset, pass a hashref of key/value pairs representing the columns of the table and the values you wish to store. If the appropriate relationships are set up, foreign key fields can also be passed an object representing the foreign row, and the value will be set to it's primary key.

To create related objects, pass a hashref for the value if the related item is a foreign key relationship ("belongs_to" in DBIx::Class::Relationship), and use the name of the relationship as the key. (NOT the name of the field, necessarily). For has_many and has_one relationships, pass an arrayref of hashrefs containing the data for each of the rows to create in the foreign tables, again using the relationship name as the key.

Instead of hashrefs of plain related data (key/value pairs), you may also pass new or inserted objects. New objects (not inserted yet, see "new"), will be inserted into their appropriate tables.

Effectively a shortcut for ->new_result(\%vals)->insert.

Example of creating a new row.

  $person_rs->create({
    name=>"Some Person",
	email=>"somebody@someplace.com"
  });

Example of creating a new row and also creating rows in a related has_many or has_one resultset. Note Arrayref.

$artist_rs->create(
   { artistid => 4, name => 'Manufactured Crap', cds => [ 
      { title => 'My First CD', year => 2006 },
      { title => 'Yet More Tweeny-Pop crap', year => 2007 },
    ],
   },
);

Example of creating a new row and also creating a row in a related belongs_toresultset. Note Hashref.

  $cd_rs->create({
    title=>"Music for Silly Walks",
	year=>2000,
	artist => {
	  name=>"Silly Musician",
	}
  });

find_or_create

Arguments: \%vals, \%attrs?
Return Value: $rowobject

$cd->cd_to_producer->find_or_create({ producer => $producer },
                                    { key => 'primary });

Tries to find a record based on its primary key or unique constraints; if none is found, creates one and returns that instead.

my $cd = $schema->resultset('CD')->find_or_create({
  cdid   => 5,
  artist => 'Massive Attack',
  title  => 'Mezzanine',
  year   => 2005,
});

Also takes an optional key attribute, to search by a specific key or unique constraint. For example:

my $cd = $schema->resultset('CD')->find_or_create(
  {
    artist => 'Massive Attack',
    title  => 'Mezzanine',
  },
  { key => 'cd_artist_title' }
);

Note: Because find_or_create() reads from the database and then possibly inserts based on the result, this method is subject to a race condition. Another process could create a record in the table after the find has completed and before the create has started. To avoid this problem, use find_or_create() inside a transaction.

Note: find_or_create is probably not what you want when creating a new row in a table that uses primary keys supplied by the database. Passing in a primary key column with a value of undef will cause "find" to attempt to search for a row with a value of NULL.

See also "find" and "update_or_create". For information on how to declare unique constraints, see "add_unique_constraint" in DBIx::Class::ResultSource.

update_or_create

Arguments: \%col_values, { key => $unique_constraint }?
Return Value: $rowobject

$resultset->update_or_create({ col => $val, ... });

First, searches for an existing row matching one of the unique constraints (including the primary key) on the source of this resultset. If a row is found, updates it with the other given column values. Otherwise, creates a new row.

Takes an optional key attribute to search on a specific unique constraint. For example:

# In your application
my $cd = $schema->resultset('CD')->update_or_create(
  {
    artist => 'Massive Attack',
    title  => 'Mezzanine',
    year   => 1998,
  },
  { key => 'cd_artist_title' }
);

$cd->cd_to_producer->update_or_create({ 
  producer => $producer, 
  name => 'harry',
}, { 
  key => 'primary,
});

If no key is specified, it searches on all unique constraints defined on the source, including the primary key.

If the key is specified as primary, it searches only on the primary key.

See also "find" and "find_or_create". For information on how to declare unique constraints, see "add_unique_constraint" in DBIx::Class::ResultSource.

Note: update_or_create is probably not what you want when looking for a row in a table that uses primary keys supplied by the database, unless you actually have a key value. Passing in a primary key column with a value of undef will cause "find" to attempt to search for a row with a value of NULL.

get_cache

Arguments: none
Return Value: \@cache_objects?

Gets the contents of the cache for the resultset, if the cache is set.

The cache is populated either by using the "prefetch" attribute to "search" or by calling "set_cache".

set_cache

Arguments: \@cache_objects
Return Value: \@cache_objects

Sets the contents of the cache for the resultset. Expects an arrayref of objects of the same class as those produced by the resultset. Note that if the cache is set the resultset will return the cached objects rather than re-querying the database even if the cache attr is not set.

The contents of the cache can also be populated by using the "prefetch" attribute to "search".

clear_cache

Arguments: none
Return Value: []

Clears the cache for the resultset.

related_resultset

Arguments: $relationship_name
Return Value: $resultset

Returns a related resultset for the supplied relationship name.

$artist_rs = $schema->resultset('CD')->related_resultset('Artist');

throw_exception

See "throw_exception" in DBIx::Class::Schema for details.

ATTRIBUTES

The resultset takes various attributes that modify its behavior. Here's an overview of them:

order_by

Value: ($order_by | \@order_by)

Which column(s) to order the results by. This is currently passed through directly to SQL, so you can give e.g. year DESC for a descending order on the column `year'.

Please note that if you have quote_char enabled (see "connect_info" in DBIx::Class::Storage::DBI) you will need to do \'year DESC' to specify an order. (The scalar ref causes it to be passed as raw sql to the DB, so you will need to manually quote things as appropriate.)

columns

Value: \@columns

Shortcut to request a particular set of columns to be retrieved. Adds me. onto the start of any column without a . in it and sets select from that, then auto-populates as from select as normal. (You may also use the cols attribute, as in earlier versions of DBIC.)

include_columns

Value: \@columns

Shortcut to include additional columns in the returned results - for example

$schema->resultset('CD')->search(undef, {
  include_columns => ['artist.name'],
  join => ['artist']
});

would return all CDs and include a 'name' column to the information passed to object inflation. Note that the 'artist' is the name of the column (or relationship) accessor, and 'name' is the name of the column accessor in the related table.

select

Value: \@select_columns

Indicates which columns should be selected from the storage. You can use column names, or in the case of RDBMS back ends, function or stored procedure names:

$rs = $schema->resultset('Employee')->search(undef, {
  select => [
    'name',
    { count => 'employeeid' },
    { sum => 'salary' }
  ]
});

When you use function/stored procedure names and do not supply an as attribute, the column names returned are storage-dependent. E.g. MySQL would return a column named count(employeeid) in the above example.

+select

Indicates additional columns to be selected from storage. Works the same as "select" but adds columns to the selection.

+as

Indicates additional column names for those added via "+select".

as

Value: \@inflation_names

Indicates column names for object inflation. That is, as indicates the name that the column can be accessed as via the get_column method (or via the object accessor, if one already exists). It has nothing to do with the SQL code SELECT foo AS bar.

The as attribute is used in conjunction with select, usually when select contains one or more function or stored procedure names:

$rs = $schema->resultset('Employee')->search(undef, {
  select => [
    'name',
    { count => 'employeeid' }
  ],
  as => ['name', 'employee_count'],
});

my $employee = $rs->first(); # get the first Employee

If the object against which the search is performed already has an accessor matching a column name specified in as, the value can be retrieved using the accessor as normal:

my $name = $employee->name();

If on the other hand an accessor does not exist in the object, you need to use get_column instead:

my $employee_count = $employee->get_column('employee_count');

You can create your own accessors if required - see DBIx::Class::Manual::Cookbook for details.

Please note: This will NOT insert an AS employee_count into the SQL statement produced, it is used for internal access only. Thus attempting to use the accessor in an order_by clause or similar will fail miserably.

To get around this limitation, you can supply literal SQL to your select attibute that contains the AS alias text, eg:

select => [\'myfield AS alias']

join

Value: ($rel_name | \@rel_names | \%rel_names)

Contains a list of relationships that should be joined for this query. For example:

# Get CDs by Nine Inch Nails
my $rs = $schema->resultset('CD')->search(
  { 'artist.name' => 'Nine Inch Nails' },
  { join => 'artist' }
);

Can also contain a hash reference to refer to the other relation's relations. For example:

package MyApp::Schema::Track;
use base qw/DBIx::Class/;
__PACKAGE__->table('track');
__PACKAGE__->add_columns(qw/trackid cd position title/);
__PACKAGE__->set_primary_key('trackid');
__PACKAGE__->belongs_to(cd => 'MyApp::Schema::CD');
1;

# In your application
my $rs = $schema->resultset('Artist')->search(
  { 'track.title' => 'Teardrop' },
  {
    join     => { cd => 'track' },
    order_by => 'artist.name',
  }
);

You need to use the relationship (not the table) name in conditions, because they are aliased as such. The current table is aliased as "me", so you need to use me.column_name in order to avoid ambiguity. For example:

# Get CDs from 1984 with a 'Foo' track 
my $rs = $schema->resultset('CD')->search(
  { 
    'me.year' => 1984,
    'tracks.name' => 'Foo'
  },
  { join => 'tracks' }
);

If the same join is supplied twice, it will be aliased to <rel>_2 (and similarly for a third time). For e.g.

my $rs = $schema->resultset('Artist')->search({
  'cds.title'   => 'Down to Earth',
  'cds_2.title' => 'Popular',
}, {
  join => [ qw/cds cds/ ],
});

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 prefetch below.

For more help on using joins with search, see DBIx::Class::Manual::Joining.

prefetch

Value: ($rel_name | \@rel_names | \%rel_names)

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

DBIx::Class has no need to go back to the database when we access the cd or artist relationships, which saves us two SQL statements in this case.

Simple prefetches will be joined automatically, so there is no need for a join attribute in the above search.

prefetch can be used with the following relationship types: belongs_to, has_one (or if you're using add_relationship, any relationship declared with an accessor type of 'single' or 'filter'). A more complex example that prefetches an artists cds, the tracks on those cds, and the tags associted with that artist is given below (assuming many-to-many from artists to tags):

my $rs = $schema->resultset('Artist')->search(
  undef,
  {
    prefetch => [
      { cds => 'tracks' },
      { artist_tags => 'tags' }
    ]
  }
);

NOTE: If you specify a prefetch attribute, the join and select attributes will be ignored.

rows

Value: $rows

Specifes the maximum number of rows for direct retrieval or the number of rows per page if the page attribute or method is used.

offset

Value: $offset

Specifies the (zero-based) row number for the first row to be returned, or the of the first row of the first page if paging is used.

group_by

Value: \@columns

A arrayref of columns to group by. Can include columns of joined tables.

group_by => [qw/ column1 column2 ... /]

having

Value: $condition

HAVING is a select statement attribute that is applied between GROUP BY and ORDER BY. It is applied to the after the grouping calculations have been done.

having => { 'count(employee)' => { '>=', 100 } }

distinct

Value: (0 | 1)

Set to 1 to group by all columns.

where

Adds to the WHERE clause.

# only return rows WHERE deleted IS NULL for all searches
__PACKAGE__->resultset_attributes({ where => { deleted => undef } }); )

Can be overridden by passing { where = undef }> as an attribute to a resulset.

cache

Set to 1 to cache search results. This prevents extra SQL queries if you revisit rows in your ResultSet:

my $resultset = $schema->resultset('Artist')->search( undef, { cache => 1 } );

while( my $artist = $resultset->next ) {
  ... do stuff ...
}

$rs->first; # without cache, this would issue a query

By default, searches are not cached.

For more examples of using these attributes, see DBIx::Class::Manual::Cookbook.

from

Value: \@from_clause

The from attribute gives you manual control over the FROM clause of SQL statements generated by DBIx::Class, allowing you to express custom JOIN clauses.

NOTE: Use this on your own risk. This allows you to shoot off your foot!

join will usually do what you need and it is strongly recommended that you avoid using from unless you cannot achieve the desired result using join. And we really do mean "cannot", not just tried and failed. Attempting to use this because you're having problems with join is like trying to use x86 ASM because you've got a syntax error in your C. Trust us on this.

Now, if you're still really, really sure you need to use this (and if you're not 100% sure, ask the mailing list first), here's an explanation of how this works.

The syntax is as follows -

[
  { <alias1> => <table1> },
  [
    { <alias2> => <table2>, -join_type => 'inner|left|right' },
    [], # nested JOIN (optional)
    { <table1.column1> => <table2.column2>, ... (more conditions) },
  ],
  # More of the above [ ] may follow for additional joins
]

<table1> <alias1>
JOIN
  <table2> <alias2>
  [JOIN ...]
ON <table1.column1> = <table2.column2>
<more joins may follow>

An easy way to follow the examples below is to remember the following:

Anything inside "[]" is a JOIN
Anything inside "{}" is a condition for the enclosing JOIN

The following examples utilize a "person" table in a family tree application. In order to express parent->child relationships, this table is self-joined:

# Person->belongs_to('father' => 'Person');
# Person->belongs_to('mother' => 'Person');

from can be used to nest joins. Here we return all children with a father, then search against all mothers of those children:

$rs = $schema->resultset('Person')->search(
    undef,
    {
        alias => 'mother', # alias columns in accordance with "from"
        from => [
            { mother => 'person' },
            [
                [
                    { child => 'person' },
                    [
                        { father => 'person' },
                        { 'father.person_id' => 'child.father_id' }
                    ]
                ],
                { 'mother.person_id' => 'child.mother_id' }
            ],
        ]
    },
);

# Equivalent SQL:
# SELECT mother.* FROM person mother
# JOIN (
#   person child
#   JOIN person father
#   ON ( father.person_id = child.father_id )
# )
# ON ( mother.person_id = child.mother_id )

The type of any join can be controlled manually. To search against only people with a father in the person table, we could explicitly use INNER JOIN:

$rs = $schema->resultset('Person')->search(
    undef,
    {
        alias => 'child', # alias columns in accordance with "from"
        from => [
            { child => 'person' },
            [
                { father => 'person', -join_type => 'inner' },
                { 'father.id' => 'child.father_id' }
            ],
        ]
    },
);

# Equivalent SQL:
# SELECT child.* FROM person child
# INNER JOIN person father ON child.father_id = father.id

for

Value: ( 'update' | 'shared' )

Set to 'update' for a SELECT ... FOR UPDATE or 'shared' for a SELECT ... FOR SHARED.

To install DBIx::Class, copy and paste the appropriate command in to your terminal.

cpanm

cpanm DBIx::Class

CPAN shell

perl -MCPAN -e shell
install DBIx::Class

For more information on module installation, please visit the detailed CPAN module installation guide.

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