NAME
DBIx::Class::ResultSet - Represents a query used for fetching a set of results.
SYNOPSIS
my $users_rs = $schema->resultset('User');
my $registered_users_rs = $schema->resultset('User')->search({ registered => 1 });
my @cds_in_2005 = $schema->resultset('CD')->search({ year => 2005 })->all();DESCRIPTION
A ResultSet is an object which stores a set of conditions representing a query. It is the backbone of DBIx::Class (i.e. the really important/useful bit).
No SQL is executed on the database when a ResultSet is created, it just stores all the conditions needed to create the query.
A basic ResultSet representing the data of an entire table is returned by calling resultset on a DBIx::Class::Schema and passing in a Source name.
my $users_rs = $schema->resultset('User');A new ResultSet is returned from calling "search" on an existing ResultSet. The new one will contain all the conditions of the original, plus any new conditions added in the search call.
A ResultSet is also an iterator. "next" is used to return all the DBIx::Class::Rows the ResultSet represents.
The query that the ResultSet represents is only executed against the database when these methods are called:
EXAMPLES
Chaining resultsets
Let's say you've got a query that needs to be run to return some data to the user. But, you have an authorization system in place that prevents certain users from seeing certain information. So, you want to construct the basic query in one method, but add constraints to it in another.
sub get_data {
my $self = shift;
my $request = $self->get_request; # Get a request object somehow.
my $schema = $self->get_schema; # Get the DBIC schema object somehow.
my $cd_rs = $schema->resultset('CD')->search({
title => $request->param('title'),
year => $request->param('year'),
});
$self->apply_security_policy( $cd_rs );
return $cd_rs->all();
}
sub apply_security_policy {
my $self = shift;
my ($rs) = @_;
return $rs->search({
subversive => 0,
});
}Resolving conditions and attributes
When a resultset is chained from another resultset, conditions and attributes with the same keys need resolving.
"join", "prefetch", "+select", "+as" attributes are merged into the existing ones from the original resultset.
The "where", "having" attribute, and any search conditions are merged with an SQL AND to the existing condition from the original resultset.
All other attributes are overridden by any new ones supplied in the search attributes.
Multiple queries
Since a resultset just defines a query, you can do all sorts of things with it with the same object.
# Don't hit the DB yet.
my $cd_rs = $schema->resultset('CD')->search({
title => 'something',
year => 2009,
});
# Each of these hits the DB individually.
my $count = $cd_rs->count;
my $most_recent = $cd_rs->get_column('date_released')->max();
my @records = $cd_rs->all;And it's not just limited to SELECT statements.
$cd_rs->delete();This is even cooler:
$cd_rs->create({ artist => 'Fred' });Which is the same as:
$schema->resultset('CD')->create({
title => 'something',
year => 2009,
artist => 'Fred'
});See: "search", "count", "get_column", "all", "create".
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
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
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 = 2004If 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
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. search_literal is a convenience method. It is equivalent to calling $schema->search(\[]), but if you want to ensure columns are bound correctly, use search.
Example of how to use search instead of search_literal
my @cds = $cd_rs->search_literal('cdid = ? AND (artist = ? OR artist = ?)', (2, 1, 2));
my @cds = $cd_rs->search(\[ 'cdid = ? AND (artist = ? OR artist = ?)', [ 'cdid', 2 ], [ 'artist', 1 ], [ 'artist', 2 ] ]);See "Searching" in DBIx::Class::Manual::Cookbook and "Searching" in DBIx::Class::Manual::FAQ for searching techniques that do not require search_literal.
find
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.
In addition to key, "find" recognizes and applies standard resultset attributes in the same way as "search" does.
Note: If your query does not return only one row, a warning is generated:
Query returned more than one rowSee 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
$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
Returns a storage-driven cursor to the given resultset. See DBIx::Class::Cursor for more information.
single
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 rowIn 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
my $max_length = $rs->get_column('length')->max;Returns a DBIx::Class::ResultSetColumn instance for a column of the ResultSet.
search_like
# WHERE title LIKE '%blue%'
$cd_rs = $rs->search_like({ title => '%blue%'});Performs a search, but uses LIKE instead of = as the condition. Note that this is simply a convenience method retained for ex Class::DBI users. You most likely want to use "search" with specific operators.
For more information, see DBIx::Class::Manual::Cookbook.
This method is deprecated and will be removed in 0.09. Use "search()" instead. An example conversion is:
->search_like({ foo => 'bar' });
# Becomes
->search({ foo => { like => 'bar' } });slice
Returns a resultset or object list representing a subset of elements from the resultset slice is called on. Indexes are from 0, i.e., to get the first three records, call:
my ($one, $two, $three) = $rs->slice(0, 2);next
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
An accessor for the primary ResultSource object from which this ResultSet is derived.
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
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
Counts the results in a literal query. Equivalent to calling "search_literal" with the passed arguments, then "count".
all
Returns all elements in the resultset. Called implicitly if the resultset is returned in list context.
reset
Resets the resultset's cursor, so you can iterate through the elements again.
first
Resets the resultset and returns an object for the first result (if the resultset returns anything).
update
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
Fetches all objects and updates them one at a time. Note that update_all will run DBIC cascade triggers, while "update" will not.
delete
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 riskIn 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
Fetches all objects and deletes them one at a time. Note that delete_all will run DBIC cascade triggers, while "delete" will not.
populate
Accepts either an arrayref of hashrefs or alternatively an arrayref of arrayrefs. For the arrayref of hashrefs style each hashref should be a structure suitable forsubmitting 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'For the arrayref of arrayrefs style, the first element should be a list of the fieldsnames to which the remaining elements are rows being inserted. For example:
$Arstist_rs->populate([
[qw/artistid name/],
[100, 'A Formally Unknown Singer'],
[101, 'A singer that jumped the shark two albums ago'],
[102, 'An actually cool singer.'],
]);Please note an important effect on your data when choosing between void and wantarray context. Since void context goes straight to insert_bulk in DBIx::Class::Storage::DBI this will skip any component that is overriding c<insert>. So if you are using something like DBIx-Class-UUIDColumns to create primary keys for you, you will find that your PKs are empty. In this case you will have to use the wantarray context in order to create those values.
_normalize_populate_args ($args)
Private method used by "populate" to normalize its incoming arguments. Factored out in case you want to subclass and accept new argument structures to the "populate" method.
pager
Return Value a Data::Page object for the current resultset. Only makes sense for queries with a page attribute.
To get the full count of entries for a paged resultset, call total_entries on the Data::Page object.
page
Returns a resultset for the $page_number page of the resultset on which page is called, where each page contains a number of rows equal to the 'rows' attribute set on the resultset (10 by default).
new_result
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.
as_query (EXPERIMENTAL)
Returns the SQL query and bind vars associated with the invocant.
This is generally used as the RHS for a subquery.
NOTE: This feature is still experimental.
find_or_new
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 its 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 its 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
$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
$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
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
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
Clears the cache for the resultset.
related_resultset
Returns a related resultset for the supplied relationship name.
$artist_rs = $schema->resultset('CD')->related_resultset('Artist');current_source_alias
Returns the current table alias for the result source this resultset is built on, that will be used in the SQL query. Usually it is me.
Currently the source alias that refers to the result set returned by a "search"/"find" family method depends on how you got to the resultset: it's me by default, but eg. "search_related" aliases it to the related result source name (and keeps me referring to the original result set). The long term goal is to make DBIx::Class always alias the current resultset as me (and make this method unnecessary).
Thus it's currently necessary to use this method in predefined queries (see "Predefined searches" in DBIx::Class::Manual::Cookbook) when referring to the source alias of the current result set:
# in a result set class
sub modified_by {
my ($self, $user) = @_;
my $me = $self->current_source_alias;
return $self->search(
"$me.modified" => $user->id,
);
}throw_exception
See "throw_exception" in DBIx::Class::Schema for details.
ATTRIBUTES
Attributes are used to refine a ResultSet in various ways when searching for data. They can be passed to any method which takes an \%attrs argument. See "search", "search_rs", "find", "count".
These are in no particular order:
order_by
Which column(s) to order the results by. If a single column name, or an arrayref of names is supplied, the argument is passed through directly to SQL. The hashref syntax allows for connection-agnostic specification of ordering direction:
For descending order:
order_by => { -desc => [qw/col1 col2 col3/] }
For explicit ascending order:
order_by => { -asc => 'col' }The old scalarref syntax (i.e. order_by => \'year DESC') is still supported, although you are strongly encouraged to use the hashref syntax as outlined above.
columns
Shortcut to request a particular set of columns to be retrieved. Each column spec may be a string (a table column name), or a hash (in which case the key is the as value, and the value is used as the select expression). 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.)
+columns
Indicates additional columns to be selected from storage. Works the same as "columns" but adds columns to the selection. (You may also use the include_columns attribute, as in earlier versions of DBIC). For example:-
$schema->resultset('CD')->search(undef, {
'+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.
include_columns
Deprecated. Acts as a synonym for "+columns" for backward compatibility.
select
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
as
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 EmployeeIf 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
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
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.artistidDBIx::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 = $schema->resultset('Artist')->search(
undef,
{
prefetch => [
{ cds => 'tracks' },
{ artist_tags => 'tags' }
]
}
);NOTE: If you specify a prefetch attribute, the join and select attributes will be ignored.
page
Makes the resultset paged and specifies the page to retrieve. Effectively identical to creating a non-pages resultset and then calling ->page($page) on it.
If rows attribute is not specified it defualts to 10 rows per page.
When you have a paged resultset, "count" will only return the number of rows in the page. To get the total, use the "pager" and call total_entries on it.
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
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
A arrayref of columns to group by. Can include columns of joined tables.
group_by => [qw/ column1 column2 ... /]having
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
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 queryBy default, searches are not cached.
For more examples of using these attributes, see DBIx::Class::Manual::Cookbook.
from
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 JOINThe 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.idIf you need to express really complex joins or you need a subselect, you can supply literal SQL to from via a scalar reference. In this case the contents of the scalar will replace the table name asscoiated with the resultsource.
WARNING: This technique might very well not work as expected on chained searches - you have been warned.
# Assuming the Event resultsource is defined as:
MySchema::Event->add_columns (
sequence => {
data_type => 'INT',
is_auto_increment => 1,
},
location => {
data_type => 'INT',
},
type => {
data_type => 'INT',
},
);
MySchema::Event->set_primary_key ('sequence');
# This will get back the latest event for every location. The column
# selector is still provided by DBIC, all we do is add a JOIN/WHERE
# combo to limit the resultset
$rs = $schema->resultset('Event');
$table = $rs->result_source->name;
$latest = $rs->search (
undef,
{ from => \ "
(SELECT e1.* FROM $table e1
JOIN $table e2
ON e1.location = e2.location
AND e1.sequence < e2.sequence
WHERE e2.sequence is NULL
) me",
},
);
# Equivalent SQL (with the DBIC chunks added):
SELECT me.sequence, me.location, me.type FROM
(SELECT e1.* FROM events e1
JOIN events e2
ON e1.location = e2.location
AND e1.sequence < e2.sequence
WHERE e2.sequence is NULL
) me;for
Set to 'update' for a SELECT ... FOR UPDATE or 'shared' for a SELECT ... FOR SHARED.