DBIx::C...Cookbook(3)

💖 DBIx::Class::Manual::Cookbook 💖

okay bestie, welcome to the User Contributed Perl Documentation for DBIx::Class::Manual::Cookbook(3) — literally a whole bag of miscellaneous recipes. no cap, it's giving “everything you needed but didn't know where to look” energy. 🫶

🍓 NAME 🍓

DBIx::Class::Manual::Cookbook - Miscellaneous recipes

---

✨ SEARCHING ✨

🌸 Paged results 🌸

When you expect a large number of results, you can ask DBIx::Class for a paged resultset, which will fetch only a defined number of records at a time:

my $rs = $schema->resultset('Artist')->search(
  undef,
  {
    page => 1,  # page to return (defaults to 1)
    rows => 10, # number of results per page
  },
);

return $rs->all(); # all records for page 1

return $rs->page(2); # records for page 2

You can get a DBIx::Class::ResultSet::Pager object for the resultset — suitable for use in e.g. a template — using the "pager" method:

return $rs->pager();

🦋 Complex WHERE clauses 🦋

Sometimes you need to formulate a query using specific operators:

my @albums = $schema->resultset('Album')->search({
  artist => { 'like', '%Lamb%' },
  title  => { 'like', '%Fear of Fours%' },
});

This results in something like the following "WHERE" clause:

WHERE artist LIKE ? AND title LIKE ?

And the following bind values for the placeholders: '%Lamb%', '%Fear of Fours%'.

Other queries might require slightly more complex logic:

my @albums = $schema->resultset('Album')->search({
  -or => [
    -and => [
      artist => { 'like', '%Smashing Pumpkins%' },
      title  => 'Siamese Dream',
    ],
    artist => 'Starchildren',
  ],
});

This results in the following "WHERE" clause:

WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
  OR artist = 'Starchildren'

For more information on generating complex queries, see "WHERE CLAUSES" in SQL::Abstract::Classic.

🎀 Retrieve one and only one row from a resultset 🎀

Sometimes you need only the first "top" row of a resultset. While this can be easily done with $rs->first, it is suboptimal, as a full blown cursor for the resultset will be created and then immediately destroyed after fetching the first row object. $rs->single is designed specifically for this case — it will grab the first returned result without even instantiating a cursor.

Before replacing all your calls to first() with single() please observe the following CAVEATS:

• While single() takes a search condition just like search() does, it does _not_ accept search attributes. However one can always chain a single() to a search():

my $top_cd = $cd_rs->search({}, { order_by => 'rating' })->single;

• Since single() is the engine behind find(), it is designed to fetch a single row per database query. Thus a warning will be issued when the underlying SELECT returns more than one row. Sometimes however this usage is valid: i.e. we have an arbitrary number of cd's but only one of them is at the top of the charts at any given time. If you know what you are doing, you can silence the warning by explicitly limiting the resultset size:

my $top_cd = $cd_rs->search ({}, { order_by => 'rating', rows => 1 })->single;

💅 Arbitrary SQL through a custom ResultSource 💅

Sometimes you have to run arbitrary SQL because your query is too complex — e.g. it contains Unions, Sub-Selects, Stored Procedures, etc. — or has to be optimized for your database in a special way, but you still want to get the results as a DBIx::Class::ResultSet.

This is accomplished by defining a ResultSource::View for your query, almost like you would define a regular ResultSource.

package My::Schema::Result::UserFriendsComplex;
use strict;
use warnings;
use base qw/DBIx::Class::Core/;

__PACKAGE__->table_class('DBIx::Class::ResultSource::View');

# For the time being this is necessary even for virtual views
__PACKAGE__->table($view_name);

#
# ->add_columns, etc.
#

# do not attempt to deploy() this view
__PACKAGE__->result_source_instance->is_virtual(1);

__PACKAGE__->result_source_instance->view_definition(q[
  SELECT u.* FROM user u
  INNER JOIN user_friends f ON u.id = f.user_id
  WHERE f.friend_user_id = ?
  UNION
  SELECT u.* FROM user u
  INNER JOIN user_friends f ON u.id = f.friend_user_id
  WHERE f.user_id = ?
]);

Next, you can execute your complex query using bind parameters like this:

my $friends = $schema->resultset( 'UserFriendsComplex' )->search( {},
  {
    bind  => [ 12345, 12345 ]
  }
);

... and you'll get back a perfect DBIx::Class::ResultSet — except, of course, that you cannot modify the rows it contains, e.g. cannot call update or delete on it.

Note that you cannot have bind parameters unless is_virtual is set to true.

• NOTE — If you're using the old deprecated "$rsrc_instance->name(\'( SELECT ...')" method for custom SQL execution, you are highly encouraged to update your code to use a virtual view as above. If you do not want to change your code, and just want to suppress the deprecation warning when you call "deploy" in DBIx::Class::Schema, add this line to your source definition, so that "deploy" will exclude this "table":

sub sqlt_deploy_hook { $_[1]->schema->drop_table ($_[1]) }

🌈 Using specific columns 🌈

When you only want specific columns from a table, you can use "columns" to specify which ones you need. This is useful to avoid loading columns with large amounts of data that you aren't about to use anyway:

my $rs = $schema->resultset('Artist')->search(
  undef,
  {
    columns => [qw/ name /]
  }
);

# Equivalent SQL:
# SELECT artist.name FROM artist

This is a shortcut for "select" and "as", see below. "columns" cannot be used together with "select" and "as".

⭐ Using database functions or stored procedures ⭐

The combination of "select" and "as" can be used to return the result of a database function or stored procedure as a column value. You use "select" to specify the source for your column value — e.g. a column name, function, or stored procedure name. You then use "as" to set the column name you will use to access the returned value:

my $rs = $schema->resultset('Artist')->search(
  {},
  {
    select => [ 'name', { LENGTH => 'name' } ],
    as     => [qw/ name name_length /],
  }
);

# Equivalent SQL:
# SELECT name name, LENGTH( name )
# FROM artist

Note that the "as" attribute has absolutely nothing to do with the SQL syntax " SELECT foo AS bar " — see the documentation in "ATTRIBUTES" in DBIx::Class::ResultSet. You can control the "AS" part of the generated SQL via the "-as" field attribute as follows:

my $rs = $schema->resultset('Artist')->search(
  {},
  {
    join => 'cds',
    distinct => 1,
    '+select' => [ { count => 'cds.cdid', -as => 'amount_of_cds' } ],
    '+as' => [qw/num_cds/],
    order_by => { -desc => 'amount_of_cds' },
  }
);

# Equivalent SQL
# SELECT me.artistid, me.name, me.rank, me.charfield, COUNT( cds.cdid ) AS amount_of_cds
#   FROM artist me LEFT JOIN cd cds ON cds.artist = me.artistid
# GROUP BY me.artistid, me.name, me.rank, me.charfield
# ORDER BY amount_of_cds DESC

If your alias exists as a column in your base class — i.e. it was added with add_columns — you just access it as normal. Our "Artist" class has a "name" column, so we just use the "name" accessor:

my $artist = $rs->first();
my $name = $artist->name();

If on the other hand the alias does not correspond to an existing column, you have to fetch the value using the "get_column" accessor:

my $name_length = $artist->get_column('name_length');

If you don't like using "get_column", you can always create an accessor for any of your aliases using either of these:

# Define accessor manually:
sub name_length { shift->get_column('name_length'); }

# Or use DBIx::Class::AccessorGroup:
__PACKAGE__->mk_group_accessors('column' => 'name_length');

See also "Using SQL functions on the left hand side of a comparison".

🧚 SELECT DISTINCT with multiple columns 🧚

my $rs = $schema->resultset('Artist')->search(
  {},
  {
    columns => [ qw/artist_id name rank/ ],
    distinct => 1
  }
);

my $rs = $schema->resultset('Artist')->search(
  {},
  {
    columns => [ qw/artist_id name rank/ ],
    group_by => [ qw/artist_id name rank/ ],
  }
);

# Equivalent SQL:
# SELECT me.artist_id, me.name, me.rank
# FROM artist me
# GROUP BY artist_id, name, rank

💜 SELECT COUNT(DISTINCT colname) 💜

my $rs = $schema->resultset('Artist')->search(
  {},
  {
    columns => [ qw/name/ ],
    distinct => 1
  }
);

my $rs = $schema->resultset('Artist')->search(
  {},
  {
    columns => [ qw/name/ ],
    group_by => [ qw/name/ ],
  }
);

my $count = $rs->count;

# Equivalent SQL:
# SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) me:

🔥 Grouping results 🔥

DBIx::Class supports "GROUP BY" as follows:

my $rs = $schema->resultset('Artist')->search(
  {},
  {
    join     => [qw/ cds /],
    select   => [ 'name', { count => 'cds.id' } ],
    as       => [qw/ name cd_count /],
    group_by => [qw/ name /]
  }
);

# Equivalent SQL:
# SELECT name, COUNT( cd.id ) FROM artist
# LEFT JOIN cd ON artist.id = cd.artist
# GROUP BY name

Please see "ATTRIBUTES" in DBIx::Class::ResultSet documentation if you are in any way unsure about the use of the attributes above — " join ", " select ", " as " and " group_by ".

🐚 Subqueries 🐚

You can write subqueries relatively easily in DBIC.

my $inside_rs = $schema->resultset('Artist')->search({
  name => [ 'Billy Joel', 'Brittany Spears' ],
});

my $rs = $schema->resultset('CD')->search({
  artist_id => { -in => $inside_rs->get_column('id')->as_query },
});

The usual operators ( '=', '!=', -in, -not_in, etc.) are supported.

NOTE: You have to explicitly use '=' when doing an equality comparison. The following will not work:

my $rs = $schema->resultset('CD')->search({
  artist_id => $inside_rs->get_column('id')->as_query,  # does NOT work
});

🌟 Support 🌟

Subqueries are supported in the where clause — first hashref — and in the from, select, and +select attributes.

💫 Correlated subqueries 💫

         my $cdrs = $schema->resultset('CD');
         my $rs = $cdrs->search({
           year => {
             '=' => $cdrs->search(
               { artist_id => { -ident => 'me.artist_id' } },
               { alias => 'sub_query' }
             )->get_column('year')->max_rs->as_query,
           },
         });

That creates the following SQL, bestie:

         SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
           FROM cd me
         WHERE year = (
           SELECT MAX(sub_query.year)
             FROM cd sub_query
           WHERE artist_id = me.artist_id
         )

---

Predefined searches 🎀

okay so you can define searches you use all the time as methods by subclassing DBIx::Class::ResultSet:

         package My::DBIC::ResultSet::CD;
         use strict;
         use warnings;
         use base 'DBIx::Class::ResultSet';

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

             return $self->search(
                 {},
                 { order_by => 'name DESC' },
             );
         }

         1;

If you're using load_namespaces in DBIx::Class::Schema, literally just place the file into the ResultSet directory next to your Result directory, and it will be automatically loaded. Slay. ✨

If however you are still using load_classes in DBIx::Class::Schema, first tell DBIx::Class to create an instance of the ResultSet class for you, in your My::DBIC::Schema::CD class:

         # class definition as normal
         use base 'DBIx::Class::Core';
         __PACKAGE__->table('cd');

         # tell DBIC to use the custom ResultSet class
         __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');

Note that resultset_class must be called after load_components and table, or you will get errors about missing methods. No skipping, bestie — order matters. 💅

Then call your new method in your code:

          my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();

---

Using SQL functions on the left hand side of a comparison 💅

Using SQL functions on the left hand side of a comparison is generally not a good idea since it requires a scan of the entire table. (Unless your RDBMS supports indexes on expressions — including return values of functions — and you create an index on the return value of the function in question.) iykyk 😭 However, it can be accomplished with DBIx::Class when necessary by resorting to literal SQL:

         $rs->search(
           \[ 'YEAR(date_of_birth) = ?', 1979 ]
         );

         # Equivalent SQL:
         # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?

To include the function as part of a larger search, use the -and keyword to collect the search conditions:

         $rs->search({ -and => [
           name => 'Bob',
           \[ 'YEAR(date_of_birth) = ?', 1979 ]
         ]});

         # Equivalent SQL:
         # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?

Note: the syntax for specifying the bind value's datatype and value is explained in "DBIC BIND VALUES" in DBIx::Class::ResultSet.

See also "Literal SQL with placeholders and bind values (subqueries)" in SQL::Abstract::Classic. 🦋

---

Software Limits 🫶

When your RDBMS does not have a working SQL limit mechanism (e.g. Sybase ASE) and GenericSubQ is either too slow or does not work at all, you can try the software_limit DBIx::Class::ResultSet attribute, which skips over records to simulate limits in the Perl layer. yes, it's doing the limit thing in Perl, iconic but also a little unhinged 🎀

For example:

         my $paged_rs = $rs->search({}, {
           rows => 25,
           page => 3,
           order_by => [ 'me.last_name' ],
           software_limit => 1,
         });

You can set it as a default for your schema by placing the following in your Schema.pm:

         __PACKAGE__->default_resultset_attributes({ software_limit => 1 });

WARNING: If you are dealing with large resultsets and your DBI or ODBC/ADO driver does not have proper cursor support (i.e. it loads the whole resultset into memory) then this feature will be extremely slow and use huge amounts of memory at best, and may cause your process to run out of memory and cause instability on your server at worst, beware! 💀

✨ JOINS AND PREFETCHING ✨

🎀 Using joins and prefetch

okay so bestie, listen — you can use the join attribute to let yourself search on, or sort your results by, one or more columns in a related table. it's giving "main character who knows everyone" energy 💅

this does require that you've already defined the DBIx::Class::Relationship. like this, for example:

  My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');

so if you wanna return all the CDs matching a particular artist name, you just pass the name of the relationship ('artists'):

  my $rs = $schema->resultset('CD')->search(
    {
      'artists.name' => 'Bob Marley'
    },
    {
      join => 'artists', # join the artist table
    }
  );

  # Equivalent SQL:
  # SELECT cd.* FROM cd
  # JOIN artist ON cd.artist = artist.id
  # WHERE artist.name = 'Bob Marley'

and notice how in that example, both the join and the condition use the relationship name instead of the table name? iconic. (peep DBIx::Class::Manual::Joining if you want the full tea on aliasing 🫖)

if you need to, you can now sort on any column in the related tables by dropping it into your order_by attribute — again, using the aliased relation name, not the table name:

  my $rs = $schema->resultset('CD')->search(
    {
      'artists.name' => 'Bob Marley'
    },
    {
      join     => 'artists',
      order_by => [qw/ artists.name /]
    }
  );

  # Equivalent SQL:
  # SELECT cd.* FROM cd
  # JOIN artist ON cd.artist = artist.id
  # WHERE artist.name = 'Bob Marley'
  # ORDER BY artist.name

⚠️ heads up bestie: the join attribute should only be used when you actually need to search or sort using columns in a related table. joining related tables when you only need columns from the main table will make performance worse! no cap, don't do it 💀

so like, now let's say you wanna display a list of CDs, each one with the name of the artist. this totally works fine:

  while (my $cd = $rs->next) {
    print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
  }

but uh 😭 there's a problem. we searched both the cd and artist tables in our main query, but we only returned data from the cd table. so to get the artist name for any of the CD objects returned, DBIx::Class has to go back to the database:

  SELECT artist.* FROM artist WHERE artist.id = ?

and a statement like that one runs for each and every CD returned by our main query. five CDs, five extra queries. a hundred CDs, a hundred extra queries. not slay. 🙈

thankfully — and this is the good part — DBIx::Class has a prefetch attribute to solve this whole situation. it lets you fetch results from related tables in advance:

  my $rs = $schema->resultset('CD')->search(
    {
      'artists.name' => 'Bob Marley'
    },
    {
      join     => 'artists',
      order_by => [qw/ artists.name /],
      prefetch => 'artists' # return artist data too!
    }
  );

  # Equivalent SQL (note SELECT from both "cd" and "artist"):
  # SELECT cd.*, artist.* FROM cd
  # JOIN artist ON cd.artist = artist.id
  # WHERE artist.name = 'Bob Marley'
  # ORDER BY artist.name

and the code to print the CD list stays exactly the same:

  while (my $cd = $rs->next) {
    print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
  }

DBIx::Class has now prefetched all the matching data from the artist table, so no additional SQL statements get executed. you now have a much more efficient query. obsessed honestly 💖

⚠️ also note that prefetch should only be used when you know you'll definitely use data from a related table. pre-fetching related tables when you only need columns from the main table will make performance worse! same vibe check as before 🌸

---

🦋 Multiple joins

in the examples above, the join attribute was a scalar. but if you pass an array reference instead, you can join to multiple tables at once 👑

in this example we wanna limit the search further, using LinerNotes:

  # Relationships defined elsewhere:
  # CD->belongs_to('artist' => 'Artist');
  # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
  my $rs = $schema->resultset('CD')->search(
    {
      'artist.name' => 'Bob Marley'
      'liner_notes.notes' => { 'like', '%some text%' },
    },
    {
      join     => [qw/ artist liner_notes /],
      order_by => [qw/ artist.name /],
    }
  );

  # Equivalent SQL:
  # SELECT cd.*, artist.*, liner_notes.* FROM cd
  # JOIN artist ON cd.artist = artist.id
  # JOIN liner_notes ON cd.id = liner_notes.cd
  # WHERE artist.name = 'Bob Marley' AND liner_notes.notes LIKE '%some text%'
  # ORDER BY artist.name

---

💜 Multi-step joins

sometimes you wanna join more than one relationship deep. it's giving "friend of a friend of a friend" 😌 in this example, we wanna find all the Artist objects who have CDs whose LinerNotes contain a specific string:

  # Relationships defined elsewhere:
  # Artist->has_many('cds' => 'CD', 'artist');
  # CD->has_one('liner_notes' => 'LinerNotes', 'cd');

  my $rs = $schema->resultset('Artist')->search(
    {
      'liner_notes.notes' => { 'like', '%some text%' },
    },
    {
      join => {
        'cds' => 'liner_notes'
      }
    }
  );

  # Equivalent SQL:
  # SELECT artist.* FROM artist
  # LEFT JOIN cd ON artist.id = cd.artist
  # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
  # WHERE liner_notes.notes LIKE '%some text%'

and joins can be nested to an arbitrary level ✨ so if we decide later that we wanna reduce the number of Artists returned based on who wrote the liner notes:

  # Relationship defined elsewhere:
  # LinerNotes->belongs_to('author' => 'Person');

  my $rs = $schema->resultset('Artist')->search(
    {
      'liner_notes.notes' => { 'like', '%some text%' },
      'author.name' => 'A. Writer'
    },
    {
      join => {
        'cds' => {
          'liner_notes' => 'author'
        }
      }
    }
  );

  # Equivalent SQL:
  # SELECT artist.* FROM artist
  # LEFT JOIN cd ON artist.id = cd.artist
  # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
  # LEFT JOIN author ON author.id = liner_notes.author
  # WHERE liner_notes.notes LIKE '%some text%'
  # AND author.name = 'A. Writer'

---

🌈 Multi-step and multiple joins

with various combos of array and hash references, you can join tables in literally any combination you desire, bestie. for example, to join Artist to CD and Concert, and join CD to LinerNotes:

  # Relationships defined elsewhere:
  # Artist->has_many('concerts' => 'Concert', 'artist');

  my $rs = $schema->resultset('Artist')->search(
    { },
    {
      join => [
        {
          cds => 'liner_notes'
        },
        'concerts'
      ],
    }
  );

  # Equivalent SQL:
  # SELECT artist.* FROM artist
  # LEFT JOIN cd ON artist.id = cd.artist
  # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
  # LEFT JOIN concert ON artist.id = concert.artist

---

🧚 Multi-step prefetch

prefetch can be nested more than one relationship deep too, using the same syntax as a multi-step join 🎀

  my $rs = $schema->resultset('Tag')->search(
    {},
    {
      prefetch => {
        cd => 'artist'
      }
    }
  );

  # Equivalent SQL:
  # SELECT tag.*, cd.*, artist.* FROM tag
  # JOIN cd ON tag.cd = cd.id
  # JOIN artist ON cd.artist = artist.id

and now accessing our cd and artist relationships doesn't need any additional SQL statements:

  my $tag = $rs->first;
  print $tag->cd->artist->name;

like, zero extra queries. we love to see it 🔥

🔥 ROW-LEVEL OPERATIONS 🔥

So like, row-level stuff. The little per-object vibes. Buckle up bestie 💅

✨ Retrieving a result object's Schema ✨

Okay so you can grab a Schema object from a result object, it's literally this easy:

my $schema = $cd->result_source->schema;
# use the schema as normal:
my $artist_rs = $schema->resultset('Artist');

This is lowkey a slay when you don't want to be passing around a Schema object to every single method 🫶 like, who has the energy.

👑 Getting the value of the primary key for the last database insert 👑

AKA getting last_insert_id

Okay so shoutout to the core component PK::Auto, this is straightforward fr:

my $foo = $rs->create(\%blah);
# do more stuff
my $id = $foo->id; # foo->my_primary_key_field will also work.

Heads up bestie: if you're not using autoincrementing primary keys, this will probably not work — but then you already know the value of the last primary key anyway, so it's giving moot 💀

🎀 Stringification 🎀

Okay so the move here is the standard stringification technique using the overload module. Iconic.

To make an object stringify itself as a single column, you do something like this (replace "name" with the column/method of your choice):

use overload '""' => sub { shift->name}, fallback => 1;

For more complex stringification, you can use an anonymous subroutine:

use overload '""' => sub { $_[0]->name . ", " .
                           $_[0]->address }, fallback => 1;

💖 Stringification Example 💖

Suppose we have two tables: "Product" and "Category". The table specifications are:

Product(id, Description, category)
Category(id, Description)

So "category" is a foreign key into the Category table. Noted 📝

Now if you have a Product object $obj and write something like

print $obj->category

things will not work as expected. Like... at all. 🙈

To obtain, for example, the category description, you should add this method to the class defining the Category table:

use overload "" => sub {
    my $self = shift;

    return $self->Description;
}, fallback => 1;

💀 Want to know if find_or_create found or created a row? 💀

Just use "find_or_new" instead, then check "in_storage":

my $obj = $rs->find_or_new({ blah => 'blarg' });
unless ($obj->in_storage) {
  $obj->insert;
  # do whatever else you wanted if it was a new row
}

Obsessed with how clean that is, no cap ✨

🦋 Static sub-classing DBIx::Class result classes 🦋

AKA adding additional relationships/methods/etc. to a model for a specific usage of the (shared) model.

🌸 Schema definition 🌸

package My::App::Schema;

use base 'DBIx::Class::Schema';

# load subclassed classes from My::App::Schema::Result/ResultSet
__PACKAGE__->load_namespaces;

# load classes from shared model
load_classes({
    'My::Shared::Model::Result' => [qw/
        Foo
        Bar
    /]});

1;

🌈 Result-Subclass definition 🌈

package My::App::Schema::Result::Baz;

use strict;
use warnings;
use base 'My::Shared::Model::Result::Baz';

# WARNING: Make sure you call table() again in your subclass,
# otherwise DBIx::Class::ResultSourceProxy::Table will not be called
# and the class name is not correctly registered as a source
__PACKAGE__->table('baz');

sub additional_method {
    return "I'm an additional method only needed by this app";
}

1;

Bestie, do not skip that table() call in your subclass 😭 if you do, DBIx::Class::ResultSourceProxy::Table will not be called and the class name is not correctly registered as a source. That warning is there for a reason, fr fr.

🧚 Dynamic Sub-classing DBIx::Class proxy classes 🧚

AKA multi-class object inflation from one table

Okay so here's the tea: DBIx::Class classes are proxy classes, therefore some different techniques need to be employed for more than basic subclassing. In this example we have a single user table that carries a boolean bit for admin. We would like to give the admin users objects (DBIx::Class::Row) the same methods as a regular user but also special admin only methods. It doesn't make sense to create two separate proxy-class files for this. We would be copying all the user methods into the Admin class. There is a cleaner way to accomplish this. Slay 💅

Overriding the "inflate_result" method within the User proxy-class gives us the effect we want. This method is called by DBIx::Class::ResultSet when inflating a result from storage. So we grab the object being returned, inspect the values we are looking for, bless it if it's an admin object, and then return it. See the example below:

⭐ Schema Definition ⭐

package My::Schema;

use base qw/DBIx::Class::Schema/;

__PACKAGE__->load_namespaces;

1;

💜 Proxy-Class definitions 💜

package My::Schema::Result::User;

use strict;
use warnings;
use base qw/DBIx::Class::Core/;

### Define what our admin class is, for ensure_class_loaded()
my $admin_class = __PACKAGE__ . '::Admin';

__PACKAGE__->table('users');

__PACKAGE__->add_columns(qw/user_id   email    password
                            firstname lastname active
                            admin/);

__PACKAGE__->set_primary_key('user_id');

sub inflate_result {
    my $self = shift;
    my $ret = $self->next::method(@_);
    if( $ret->admin ) {### If this is an admin, rebless for extra functions
        $self->ensure_class_loaded( $admin_class );
        bless $ret, $admin_class;
    }
    return $ret;
}

sub hello {
    print "I am a regular user.\n";
    return ;
}

1;

package My::Schema::Result::User::Admin;

use strict;
use warnings;
use base qw/My::Schema::Result::User/;

# This line is important
__PACKAGE__->table('users');

sub hello
{
    print "I am an admin.\n";
    return;
}

sub do_admin_stuff
{
    print "I am doing admin stuff\n";
    return ;
}

1;

🍓 Test File test.pl 🍓

use warnings;
use strict;
use My::Schema;

my $user_data = { email    => 'someguy@place.com',
                  password => 'pass1',
                  admin    => 0 };

my $admin_data = { email    => 'someadmin@adminplace.com',
                   password => 'pass2',
                   admin    => 1 };

my $schema = My::Schema->connection('dbi:Pg:dbname=test');

$schema->resultset('User')->create( $user_data );
$schema->resultset('User')->create( $admin_data );

### Now we search for them
my $user = $schema->resultset('User')->single( $user_data );
my $admin = $schema->resultset('User')->single( $admin_data );

print ref $user, "\n";
print ref $admin, "\n";

print $user->password , "\n"; # pass1
print $admin->password , "\n";# pass2; inherited from User
print $user->hello , "\n";# I am a regular user.
print $admin->hello, "\n";# I am an admin.

### The statement below will NOT print
print "I can do admin stuff\n" if $user->can('do_admin_stuff');
### The statement below will print
print "I can do admin stuff\n" if $admin->can('do_admin_stuff');

Alternatively you can use DBIx::Class::DynamicSubclass that implements exactly the above functionality. Convenient or what 😌

💅 Skip result object creation for faster results 💅

Real talk: DBIx::Class is not built for speed, it's built for convenience and ease of use, but sometimes you just need to get the data, and skip the fancy objects. We've all been there.

To do this simply use DBIx::Class::ResultClass::HashRefInflator.

 my $rs = $schema->resultset('CD');

 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');

 my $hash_ref = $rs->find(1);

Wasn't that easy? ✨

⚠️ Beware bestie, changing the Result class using "result_class" in DBIx::Class::ResultSet will replace any existing class completely including any special components loaded using load_components, eg. DBIx::Class::InflateColumn::DateTime. Like, completely completely. Do not do this by accident 😭

🔥 Get raw data for blindingly fast results 🔥

If the HashRefInflator solution above is not fast enough for you, you can use a DBIx::Class to return values exactly as they come out of the database with none of the convenience methods wrapped round them.

This is used like so:

my $cursor = $rs->cursor
while (my @vals = $cursor->next) {
    # use $val[0..n] here
}

You will need to map the array offsets to particular columns (you can use the "select" in DBIx::Class::ResultSet attribute of "search" in DBIx::Class::ResultSet to force ordering). Keep track of your indexes, iykyk 🫶

---

🌟 RESULTSET OPERATIONS 🌟

Resultsets. The whole squad of rows. Let's go 👑

🌸 Getting Schema from a ResultSet 🌸

To get the DBIx::Class::Schema object from a ResultSet, do the following:

 $rs->result_source->schema

That's it. That's the tip. Simple queen behaviour 💅

🎀 Getting Columns Of Data 🎀

AKA Aggregating Data

If you want to find the sum of a particular column there are several ways, the obvious one is to use search:

my $rs = $schema->resultset('Items')->search(
  {},
  {
     select => [ { sum => 'Cost' } ],
     as     => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
  }
);
my $tc = $rs->first->get_column('total_cost');

Or, you can use the DBIx::Class::ResultSetColumn, which gets returned when you ask the "ResultSet" for a column using "get_column":

my $cost = $schema->resultset('Items')->get_column('Cost');
my $tc = $cost->sum;

With this you can also do:

my $minvalue = $cost->min;
my $maxvalue = $cost->max;

Or just iterate through the values of this column only:

while ( my $c = $cost->next ) {
  print $c;
}

foreach my $c ($cost->all) {
  print $c;
}

So "ResultSetColumn" only has a limited number of built-in functions. If you need one that it doesn't have, then you can use the "func" method instead:

my $avg = $cost->func('AVERAGE');

This will cause the following SQL statement to be run:

SELECT AVERAGE(Cost) FROM Items me

Which will of course only work if your database supports this function. See DBIx::Class::ResultSetColumn for more documentation. Check your DB's vibe first, bestie 🔍

🦋 Creating a result set from a set of rows 🦋

Sometimes you have a (set of) result objects that you want to put into a resultset without the need to hit the DB again. You can do that by using the set_cache method:

 my @uploadable_groups;
 while (my $group = $groups->next) {
   if ($group->can_upload($self)) {
     push @uploadable_groups, $group;
   }
 }
 my $new_rs = $self->result_source->resultset;
 $new_rs->set_cache(\@uploadable_groups);
 return $new_rs;

No extra DB trip, no extra latency, we love to see it 💖

💅 USING RELATIONSHIPS 💅

Okay bestie, relationships are where the cute stuff happens — related tables, searches across them, deletes, ordering, filtering, many-to-many bridges, cross-schema mapping, the whole vibe. Let’s go 💖

---

🎀 Create a new row in a related table 🎀

Want a fresh related row? create_related is the move:

my $author = $book->create_related('author', { name => 'Fred'});

🔍 Search in a related table 🔍

This one only searches for books named 'Titanic' by the author in $author.

my $books_rs = $author->search_related('books', { name => 'Titanic' });

💀 Delete data in a related table 💀

This deletes only the book named Titanic by the author in $author.

$author->delete_related('books', { name => 'Titanic' });

🦋 Ordering a relationship result set 🦋

If you always want a relation to be ordered, you can specify this when you create the relationship.

To order $book->pages by descending page_number, create the relation as follows:

__PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );

🌸 Filtering a relationship result set 🌸

If you want to get a filtered result set, you can just add to $attr as follows:

__PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );

🧚 Many-to-many relationship bridges 🧚

This is straightforward using ManyToMany:

package My::User;
use base 'DBIx::Class::Core';
__PACKAGE__->table('user');
__PACKAGE__->add_columns(qw/id name/);
__PACKAGE__->set_primary_key('id');
__PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
__PACKAGE__->many_to_many('addresses' => 'user_address', 'address');

package My::UserAddress;
use base 'DBIx::Class::Core';
__PACKAGE__->table('user_address');
__PACKAGE__->add_columns(qw/user address/);
__PACKAGE__->set_primary_key(qw/user address/);
__PACKAGE__->belongs_to('user' => 'My::User');
__PACKAGE__->belongs_to('address' => 'My::Address');

package My::Address;
use base 'DBIx::Class::Core';
__PACKAGE__->table('address');
__PACKAGE__->add_columns(qw/id street town area_code country/);
__PACKAGE__->set_primary_key('id');
__PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
__PACKAGE__->many_to_many('users' => 'user_address', 'user');

$rs = $user->addresses(); # get all addresses for a user
$rs = $address->users(); # get all users for an address

my $address = $user->add_to_addresses(    # returns a My::Address instance,
                                          # NOT a My::UserAddress instance!
  {
    country => 'United Kingdom',
    area_code => 'XYZ',
    town => 'London',
    street => 'Sesame',
  }
);

🌈 Relationships across DB schemas 🌈

Mapping relationships across DB schemas is easy as long as the schemas themselves are all accessible via the same DBI connection. In most cases, this means that they are on the same database host as each other and your connecting database user has the proper permissions to them.

To accomplish this one only needs to specify the DB schema name in the table declaration, like so...

package MyApp::Schema::Result::Artist;
use base qw/DBIx::Class::Core/;

__PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause

__PACKAGE__->add_columns(qw/ artist_id name /);
__PACKAGE__->set_primary_key('artist_id');
__PACKAGE__->has_many('cds' => 'MyApp::Schema::Result::Cd');

1;

Whatever string you specify there will be used to build the "FROM" clause in SQL queries.

The big drawback to this is you now have DB schema names hardcoded in your class files. This becomes especially troublesome if you have multiple instances of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and the DB schemas are named based on the environment (e.g. database1_dev).

However, one can dynamically "map" to the proper DB schema by overriding the connection method in your Schema class and building a renaming facility, like so:

package MyApp::Schema;
use Moose;

extends 'DBIx::Class::Schema';

around connection => sub {
  my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );

  my $postfix = delete $attr->{schema_name_postfix};

  $inner->(@_);

  if ( $postfix ) {
      $self->append_db_name($postfix);
  }
};

sub append_db_name {
  my ( $self, $postfix ) = @_;

  my @sources_with_db
      = grep
          { $_->name =~ /^\w+\./mx }
          map
              { $self->source($_) }
              $self->sources;

  foreach my $source (@sources_with_db) {
      my $name = $source->name;
      $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;

      $source->name($name);
  }
}

1;

By overriding the connection method and extracting a custom option from the provided \%attr hashref one can then simply iterate over all the Schema's ResultSources, renaming them as needed.

To use this facility, simply add or modify the \%attr hashref that is passed to connection, as follows:

my $schema
  = MyApp::Schema->connect(
    $dsn,
    $user,
    $pass,
    {
      schema_name_postfix => '_dev'
      # ... Other options as desired ...
    })

Obviously, one could accomplish even more advanced mapping via a hash map or a callback routine.

---

💸 TRANSACTIONS 💸

🔥 Transactions with txn_do 🔥

As of version 0.04001, there is improved transaction support in DBIx::Class::Storage and DBIx::Class::Schema. Here is an example of the recommended way to use it:

my $genus = $schema->resultset('Genus')->find(12);

my $coderef2 = sub {
  $genus->extinct(1);
  $genus->update;
};

my $coderef1 = sub {
  $genus->add_to_species({ name => 'troglodyte' });
  $genus->wings(2);
  $genus->update;
  $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
  return $genus->species;
};

use Try::Tiny;
my $rs;
try {
  $rs = $schema->txn_do($coderef1);
} catch {
  # Transaction failed
  die "the sky is falling!"           #
    if ($_ =~ /Rollback failed/);     # Rollback failed

  deal_with_failed_transaction();
};

Note: by default "txn_do" will re-run the coderef one more time if an error occurs due to client disconnection (e.g. the server is bounced). You need to make sure that your coderef can be invoked multiple times without terrible side effects.

Nested transactions will work as expected. That is, only the outermost transaction will actually issue a commit to the $dbh, and a rollback at any level of any transaction will cause the entire nested transaction to fail.

✨ Nested transactions and auto-savepoints ✨

If savepoints are supported by your RDBMS, it is possible to achieve true nested transactions with minimal effort. To enable auto-savepoints via nested transactions, supply the "auto_savepoint = 1" connection attribute.

Here is an example of true nested transactions. In the example, we start a big task which will create several rows. Generation of data for each row is a fragile operation and might fail. If we fail creating something, depending on the type of failure, we want to abort the whole task, or only skip the failed row.

my $schema = MySchema->connect("dbi:Pg:dbname=my_db");

# Start a transaction. Every database change from here on will only be
# committed into the database if the try block succeeds.
use Try::Tiny;
my $exception;
try {
  $schema->txn_do(sub {
    # SQL: BEGIN WORK;

    my $job = $schema->resultset('Job')->create({ name=> 'big job' });
    # SQL: INSERT INTO job ( name) VALUES ( 'big job' );

    for (1..10) {

      # Start a nested transaction, which in fact sets a savepoint.
      try {
        $schema->txn_do(sub {
          # SQL: SAVEPOINT savepoint_0;

          my $thing = $schema->resultset('Thing')->create({ job=>$job->id });
          # SQL: INSERT INTO thing ( job) VALUES ( 1 );

          if (rand > 0.8) {
            # This will generate an error, thus setting $@

            $thing->update({force_fail=>'foo'});
            # SQL: UPDATE thing SET force_fail = 'foo'
            #      WHERE ( id = 42 );
          }
        });
      } catch {
        # SQL: ROLLBACK TO SAVEPOINT savepoint_0;

        # There was an error while creating a $thing. Depending on the error
        # we want to abort the whole transaction, or only rollback the
        # changes related to the creation of this $thing

        # Abort the whole job
        if ($_ =~ /horrible_problem/) {
          print "something horrible happened, aborting job!";
          die $_;                # rethrow error
        }

        # Ignore this $thing, report the error, and continue with the
        # next $thing
        print "Cannot create thing: $_";
      }
      # There was no error, so save all changes since the last
      # savepoint.

      # SQL: RELEASE SAVEPOINT savepoint_0;
    }
  });
} catch {
  $exception = $_;
};

if ($exception) {
  # There was an error while handling the $job. Rollback all changes
  # since the transaction started, including the already committed
  # ('released') savepoints. There will be neither a new $job nor any
  # $thing entry in the database.

  # SQL: ROLLBACK;

  print "ERROR: $exception\n";
}
else {
  # There was no error while handling the $job. Commit all changes.
  # Only now other connections can see the newly created $job and
  # @things.

  # SQL: COMMIT;

  print "Ok\n";
}

In this example it might be hard to see where the rollbacks, releases and commits are happening, but it works just the same as for plain txn_do: If the try-block around txn_do fails, a rollback is issued. If the try succeeds, the transaction is committed (or the savepoint released).

While you can get more fine-grained control using svp_begin, svp_release and svp_rollback, it is strongly recommended to use txn_do with coderefs.

🫶 Simple Transactions with DBIx::Class::Storage::TxnScopeGuard 🫶

An easy way to use transactions is with DBIx::Class::Storage::TxnScopeGuard. See "Automatically creating related objects" for an example.

Note: unlike txn_do, TxnScopeGuard will only make sure the connection is alive when issuing the "BEGIN" statement. It will not (and really can not) retry if the server goes away mid-operations, unlike "txn_do".

---

🧚 SQL 🧚

👑 Creating Schemas From An Existing Database 👑

DBIx::Class::Schema::Loader will connect to a database and create a DBIx::Class::Schema and associated sources by examining the database.

okay so the recommended way to do this whole thing is to use the dbicdump utility or the Catalyst helper — both of those are described over in Manual::Intro, go read that bestie 💖

Or, if you're feeling indie, use the make_schema_at method instead:

perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
  -e 'make_schema_at("My::Schema", \
  { db_schema => 'myschema', components => ["InflateColumn::DateTime"] }, \
  [ "dbi:Pg:dbname=foo", "username", "password" ])'

What this does is literally grow you a whole tree of files rooted at ./lib/My/Schema/ that contain source definitions for every single table it finds in the "myschema" schema inside the "foo" database. like, all of them. no cap 🌱

---

💾 Creating DDL SQL 💾

okay heads up: everything in this bit needs you to have SQL::Translator installed first (it also goes by "SQL Fairy", iconic name tbh 🧚).

So to make a set of database-specific .sql files for that schema up above:

my $schema = My::Schema->connect($dsn);
$schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
                       '0.1',
                       './dbscriptdir/'
                       );

By default (as in, if you don't tell it otherwise) this creates schema files in the current directory, for MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm. default behaviour, slay ✨

And to make a brand new database using the schema:

my $schema = My::Schema->connect($dsn);
$schema->deploy({ add_drop_table => 1});

To import the .sql files it just made, using the mysql client:

mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql

Now — if you want "ALTER TABLE" conversion scripts so you can update a database to a newer version of your schema later on, first bump to a new $VERSION in your Schema file, and then:

my $schema = My::Schema->connect($dsn);
$schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
                        '0.2',
                        '/dbscriptdir/',
                        '0.1'
                        );

This produces new database-specific .sql files for the new version of the schema, plus scripts to convert from version 0.1 to 0.2 🔥. The catch? This requires that the files for 0.1 — as created above — are available in the given directory to diff against. no 0.1 files, no diff, no conversion scripts, periodt.

---

🔮 Select from dual 🔮

Some databases need dummy tables so you can call functions or expressions that aren't based on table content. For examples of how this applies to the various database types, go peek at: <http://troels.arvin.dk/db/rdbms/#other-dummy_table>.

⚠️ Note, and I mean this: if you're using Oracle's dual table, don't you ever do anything other than a select. If you CRUD on your dual table you will break your database. like genuinely break it. do not test this 💀

So make a table class exactly like you would for any other table:

package MyAppDB::Dual;
use strict;
use warnings;
use base 'DBIx::Class::Core';
__PACKAGE__->table("Dual");
__PACKAGE__->add_columns(
  "dummy",
  { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
);

Once your table class is loaded, select from it using "select" and "as" — not "columns":

my $rs = $schema->resultset('Dual')->search(undef,
  { select => [ 'sydate' ],
    as     => [ 'now' ]
  },
);

All you gotta do now is be careful how you access your resultset, because the below will not work — there's no column called 'now' in the Dual table class:

while (my $dual = $rs->next) {
  print $dual->now."\n";
}
# Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.

Sure, you could use 'dummy' in "as" instead of 'now', or "add_columns" to your Dual class for whatever you wanted to select from dual — but that's just silly 🙈. Instead, use "get_column":

while (my $dual = $rs->next) {
  print $dual->get_column('now')."\n";
}

Or use "cursor":

my $cursor = $rs->cursor;
while (my @vals = $cursor->next) {
  print $vals[0]."\n";
}

okay now a real one: if you're gonna use this "trick" together with "deploy" in DBIx::Class::Schema or "create_ddl_dir" in DBIx::Class::Schema, a table called "dual" will get created in your current schema. Which would overlap "sys.dual" and then you couldn't fetch "sysdate" or "sequence.nextval" from dual anymore. to dodge that whole situation, just tell SQL::Translator not to create table dual:

my $sqlt_args = {
    add_drop_table => 1,
    parser_args    => { sources => [ grep $_ ne 'Dual', schema->sources ] },
};
$schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );

Or use DBIx::Class::ResultClass::HashRefInflator:

$rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
while ( my $dual = $rs->next ) {
  print $dual->{now}."\n";
}

And here are some example "select" conditions to show off the different syntax you could use for doing stuff like "oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')" — iykyk:

# get a sequence value
select => [ 'A_SEQ.nextval' ],

# get create table sql
select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],

# get a random num between 0 and 100
select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],

# what year is it?
select => [ { 'extract' => [ \'year from sysdate' ] } ],

# do some math
select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],

# which day of the week were you born on?
select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],

# select 16 rows from dual
select   => [ "'hello'" ],
as       => [ 'world' ],
group_by => [ 'cube( 1, 2, 3, 4 )' ],

---

🛠️ Adding Indexes And Functions To Your SQL 🛠️

okay so a lot of the time you're gonna want indexes on your table's columns to speed up searching — obviously 💅. To do that, make a method called "sqlt_deploy_hook" inside the relevant source class (and if you wanna share one hook between multiple sources, go check out the advanced callback system):

package My::Schema::Result::Artist;

__PACKAGE__->table('artist');
__PACKAGE__->add_columns(id => { ... }, name => { ... })

sub sqlt_deploy_hook {
  my ($self, $sqlt_table) = @_;

  $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
}

1;

Sometimes you might want to switch up the index depending on which database type the SQL is being generated for:

my ($db_type = $sqlt_table->schema->translator->producer_type)
  =~ s/^SQL::Translator::Producer:://;

You can also stick hooks at the schema level to stop certain tables from being created at all:

package My::Schema;

...

sub sqlt_deploy_hook {
  my ($self, $sqlt_schema) = @_;

  $sqlt_schema->drop_table('table_name');
}

And if you're feeling extra, you could also add views, procedures or triggers to the output using "add_view" in SQL::Translator::Schema, "add_procedure" in SQL::Translator::Schema or "add_trigger" in SQL::Translator::Schema. the whole menu, bestie 🍓

---

🎀 Schema versioning 🎀

This next example is a ~simplistic~ lil look at how you might use DBIx::Class to deploy versioned schemas to your customers. The basic process goes like this:

1. Create a DBIx::Class schema
2. Save the schema
3. Deploy to customers
4. Modify schema to change functionality
5. Deploy update to customers

✨ Create a DBIx::Class schema ✨

You can either do this by hand, or generate it from an existing database as described under "Creating Schemas From An Existing Database".

✨ Save the schema ✨

Call "create_ddl_dir" in DBIx::Class::Schema — same as above under "Creating DDL SQL".

✨ Deploy to customers ✨

There are several ways you could deploy your schema, and honestly they're probably beyond the scope of this recipe, but they might include:

1. Require the customer to apply it manually using their RDBMS.
2. Package it along with your app, making database dump/schema update/tests all part of your install.

✨ Modify the schema to change functionality ✨

As your app evolves, you may need to modify your schema to change functionality. Once the changes are made to your schema in DBIx::Class, export the modified schema and the conversion scripts exactly like in "Creating DDL SQL".

✨ Deploy update to customers ✨

Add the DBIx::Class::Schema::Versioned schema component to your Schema class. This adds a new table to your database called "dbix_class_schema_vesion" — yes that's how it's spelled, I don't make the rules 🫶 — which keeps track of which version is installed and warns if the user tries to run a newer schema version than the database thinks it has.

Alternatively? Just send the conversion SQL scripts to your customers like above. either way works.

---

🌈 Setting quoting for the generated SQL 🌈

If your database has column names with spaces and/or reserved words in them, those bad boys need to be quoted in the SQL queries. You do that with:

$schema->storage->sql_maker->quote_char([ qw/[ ]/] );
$schema->storage->sql_maker->name_sep('.');

The first line sets the quote characters — either a pair of matching brackets, or a """ or "'":

$schema->storage->sql_maker->quote_char('"');

Check your database's documentation for the correct quote characters to use, fr fr. And "name_sep" needs to be set so the SQL generator can put the quotes in the correct place — it defaults to "." if you don't supply it.

In most cases you should set these as part of the arguments you pass to "connect" in DBIx::Class::Schema:

my $schema = My::Schema->connect(
 'dbi:mysql:my_db',
 'db_user',
 'db_password',
 {
   quote_char => '"',
   name_sep   => '.'
 }
)

Sometimes quoting is required for every user of a schema. To enforce that, you can also overload the "connection" method for your schema class:

sub connection {
    my $self = shift;
    my $rv = $self->next::method( @_ );
    $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
    $rv->storage->sql_maker->name_sep('.');
    return $rv;
}

---

🦋 Working with PostgreSQL array types 🦋

You can also assign values to PostgreSQL array columns by passing array references in the "\%columns" ("\%vals") hashref of the "create" in DBIx::Class::ResultSet and "update" in DBIx::Class::Row family of methods:

$resultset->create({
  numbers => [1, 2, 3]
});

$result->update(
  {
    numbers => [1, 2, 3]
  },
  {
    day => '2008-11-24'
  }
);

But in conditions (e.g. "\%cond" in the "search" in DBIx::Class::ResultSet family of methods) you cannot directly use array references — because that gets interpreted as a list of values to be "OR"ed 🙈. What you can do is use the following syntax to force passing them as bind values:

$resultset->search(
  {
    numbers => { -value => [1, 2, 3] }
  }
);

✨ Formatting DateTime objects in queries ✨

Okay so this one is so important bestie, listen up 💖

If your WHERE conditions contain DateTime arguments, you must format them with the DateTime formatter that datetime_parser in DBIx::Class::Storage::DBI hands you — otherwise your RDBMS has no idea what you're saying. Every Storage object attached to your Schema gives you a correct DateTime formatter, so honestly all you gotta do is:

  my $dtf = $schema->storage->datetime_parser;
  my $rs = $schema->resultset('users')->search(
    {
      signup_date => {
        -between => [
          $dtf->format_datetime($dt_start),
          $dtf->format_datetime($dt_end),
        ],
      }
    },
  );

Skip this and your query just gets the plain stringification of the DateTime object dropped into it, which almost never matches what the RDBMS expects. It's giving chaos, honestly 😭

This kludge is only necessary for conditions you pass to search and find in DBIx::Class::ResultSet. Meanwhile create and update in DBIx::Class::Row (but not update in DBIx::Class::ResultSet) are DBIx::Class::InflateColumn-aware and will do the right thing when you hand them an inflated DateTime object. Slay 🫶

---

🌈 Using Unicode 🌈

When you're working with unicode character data you've got two options, periodt:

• your database supports unicode characters (which includes setting the utf8 flag on the returned string), or
• you encode/decode data appropriately every single time a string field gets inserted into or retrieved from the database 🙈

Avoiding encode/decode entirely and leaning on your database's own unicode capabilities is much better — like, if at all possible, do that one 💅

The DBIx::Class::UTF8Columns component handles storing selected unicode columns in a database that doesn't directly support unicode. But heads up — if you use it with a database that does correctly handle unicode, then strange and unexpected data corrupt will occur 💀 no cap.

The Catalyst Wiki Unicode page at <http://wiki.catalystframework.org/wiki/tutorialsandhowtos/using_unicode> has extra info on using Unicode with Catalyst and DBIx::Class.

These databases handle unicode data correctly, bestie:

MySQL

MySQL supports unicode, and will correctly flag utf8 data coming out of the database if mysql_enable_utf8 is set in the connect options ✨

  my $schema = My::Schema->connection('dbi:mysql:dbname=test',
                                      $user, $pass,
                                      { mysql_enable_utf8 => 1} );

When it's set, data retrieved from a textual column type (char, varchar, etc) will have the UTF-8 flag turned on if necessary. That enables character semantics on that string. You'll also need to make sure your database / table / column is configured to use UTF8 — see Chapter 10 of the mysql manual for the deets. And see DBD::mysql for even further details 🎀

Oracle

Info about Oracle support for unicode lives in "UNICODE" in DBD::Oracle 👑

PostgreSQL

PostgreSQL supports unicode if the character set is correctly set at database creation time. Also, pg_enable_utf8 should be set so unicode data is correctly marked 🌸

  my $schema = My::Schema->connection('dbi:Pg:dbname=test',
                                      $user, $pass,
                                      { pg_enable_utf8 => 1} );

Further information can be found in DBD::Pg.

SQLite

SQLite version 3 and above natively use unicode internally. To correctly mark unicode strings taken from the database, the sqlite_unicode flag should be set at connect time (in versions of DBD::SQLite prior to 1.27 this attribute was named unicode) 🦋

  my $schema = My::Schema->connection('dbi:SQLite:/tmp/test.db',
                                      '', '',
                                      { sqlite_unicode => 1} );

---

🚀 BOOTSTRAPPING/MIGRATING 🚀

Easy migration from class-based to schema-based setup

So you wanna start using the schema-based approach to DBIx::Class (peep "Setting it up manually" in DBIx::Class::Manual::Intro), but you've already got an established class-based setup with so many existing classes and you are not about to move them all by hand 😭 Try this nifty script instead:

  use MyDB;
  use SQL::Translator;

  my $schema = MyDB->schema_instance;

  my $translator           =  SQL::Translator->new(
      debug                => $debug          ||  0,
      trace                => $trace          ||  0,
      no_comments          => $no_comments    ||  0,
      show_warnings        => $show_warnings  ||  0,
      add_drop_table       => $add_drop_table ||  0,
      validate             => $validate       ||  0,
      parser_args          => {
         'DBIx::Schema'    => $schema,
                              },
      producer_args   => {
          'prefix'         => 'My::Schema',
                         },
  );

  $translator->parser('SQL::Translator::Parser::DBIx::Class');
  $translator->producer('SQL::Translator::Producer::DBIx::Class::File');

  my $output = $translator->translate(@args) or die
          "Error: " . $translator->error;

  print $output;

You could use Module::Find to search for all subclasses in the MyDB::* namespace — that part is currently left as an exercise for the reader 🙈 (iykyk)

---

💅 OVERLOADING METHODS 💅

DBIx::Class uses the Class::C3 package, which provides for redispatch of method calls — super useful for things like default values and triggers. You have to use calls to next::method to overload methods. More info on using Class::C3 with DBIx::Class can be found in DBIx::Class::Manual::Component 🌟

Setting default values for a row

It's literally as simple as overriding the new method. Note the use of next::method, bestie 👑

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

    $attrs->{foo} = 'bar' unless defined $attrs->{foo};

    my $new = $class->next::method($attrs);

    return $new;
  }

For more info about next::method, look in the Class::C3 documentation. See also DBIx::Class::Manual::Component for more ways to write your own base classes to do this.

People looking for ways to do "triggers" with DBIx::Class are probably just looking for this 👀

Changing one field whenever another changes

Okay so say you have three columns: id, number, and squared. You want to make changes to number and have squared be automagically set to the value of number squared. You can pull this off by wrapping the number accessor with the around method modifier, available through either Class::Method::Modifiers, Moose or Moose-like modules 🔥

  around number => sub {
    my ($orig, $self) = (shift, shift);

    if (@_) {
      my $value = $_[0];
      $self->squared( $value * $value );
    }

    $self->$orig(@_);
  };

Note that the hard work is done by the call to $self->$orig, which redispatches your call to store_column in the superclass(es) 💖

Generally, if this is a calculation your database can easily do, try and avoid storing the calculated value. It's safer to calculate when needed than to rely on the data being in sync. No cap, that's just good sense 🌸

Automatically creating related objects

You might have a class Artist which has many CDs. Further, you want to create a CD object every time you insert an Artist object. You can accomplish this by overriding insert on your objects:

  sub insert {
    my ( $self, @args ) = @_;
    $self->next::method(@args);
    $self->create_related ('cds', \%initial_cd_data );
    return $self;
  }

And if you want to wrap the two inserts in a transaction (which for consistency is an excellent idea, honestly iconic), you can use the awesome DBIx::Class::Storage::TxnScopeGuard 🫶

  sub insert {
    my ( $self, @args ) = @_;

    my $guard = $self->result_source->schema->txn_scope_guard;

    $self->next::method(@args);
    $self->create_related ('cds', \%initial_cd_data );

    $guard->commit;

    return $self
  }

Wrapping/overloading a column accessor

Problem:

Say you have a table Camera and want to associate a description with each camera. For most cameras, you'll be able to generate the description from the other columns. However, in a few special cases you may want to associate a custom description with a camera 🎀

Solution:

In your database schema, define a description field in the Camera table that can contain text and null values.

In DBIC, we'll overload the column accessor to provide a sane default if no custom description is defined. The accessor will either return or generate the description, depending on whether the field is null or not 💅

First, in your Camera schema class, define the description field as follows:

  __PACKAGE__->add_columns(description => { accessor => '_description' });

Next, we'll define the accessor-wrapper subroutine:

  sub description {
      my $self = shift;

      # If there is an update to the column, we'll let the original accessor
      # deal with it.
      return $self->_description(@_) if @_;

      # Fetch the column value.
      my $description = $self->_description;

      # If there's something in the description field, then just return that.
      return $description if defined $description && length $descripton;

      # Otherwise, generate a description.
      return $self->generate_description;
  }

🔍 DEBUGGING AND PROFILING 🔍

💾 DBIx::Class objects with Data::Dumper

ok so Data::Dumper is literally the MVP of debugging, but sometimes it's giving "needle in a haystack" because there's so much data and you can't find the part you actually care about. like, specifically, if one naively tries to use it like this, bestie:

use Data::Dumper;

my $cd = $schema->resultset('CD')->find(1);
print Dumper($cd);

you get several pages worth of data dumped from the CD object's schema and result source straight to your screen 😭 and since usually you only want like a few column values of the object, this is not it. not helpful at all.

but luckily! you can modify the data before Data::Dumper outputs it. literally all you do is define a hook that Data::Dumper calls on the object before dumping it. for example:

package My::DB::CD;

sub _dumper_hook {
  $_[0] = bless {
    %{ $_[0] },
    result_source => undef,
  }, ref($_[0]);
}

[...]

use Data::Dumper;

local $Data::Dumper::Freezer = '_dumper_hook';

my $cd = $schema->resultset('CD')->find(1);
print Dumper($cd);
       # dumps $cd without its ResultSource

and if your schema's structure is such that there's a common base class for all your table classes? just drop a method similar to _dumper_hook in the base class and set $Data::Dumper::Freezer to its name, and Data::Dumper will automagically clean up your data before printing it. slay. see "EXAMPLES" in Data::Dumper for more info 💅

⏱️ Profiling

when you enable DBIx::Class::Storage's debugging, it prints the SQL executed plus notifications of query completion and transaction begin/commit. and if you'd like to profile the SQL, you can subclass the DBIx::Class::Storage::Statistics class and write your own profiling mechanism, like so:

package My::Profiler;
use strict;

use base 'DBIx::Class::Storage::Statistics';

use Time::HiRes qw(time);

my $start;

sub query_start {
  my $self = shift();
  my $sql = shift();
  my @params = @_;

  $self->print("Executing $sql: ".join(', ', @params)."\n");
  $start = time();
}

sub query_end {
  my $self = shift();
  my $sql = shift();
  my @params = @_;

  my $elapsed = sprintf("%0.4f", time() - $start);
  $self->print("Execution took $elapsed seconds.\n");
  $start = undef;
}

1;

then you install that class as the debugging object:

__PACKAGE__->storage->debugobj(new My::Profiler());
__PACKAGE__->storage->debug(1);

a more complicated example might involve storing each execution of SQL in an array:

sub query_end {
  my $self = shift();
  my $sql = shift();
  my @params = @_;

  my $elapsed = time() - $start;
  push(@{ $calls{$sql} }, {
      params => \@params,
      elapsed => $elapsed
  });
}

and then you could create average, high and low execution times for an SQL statement and dig down to see if certain parameters cause aberrant behavior 👀 you might wanna check out DBIx::Class::QueryLog as well. iykyk.

---

🚀 IMPROVING PERFORMANCE 🚀

ok bestie, speed run, go:

• install Class::XSAccessor to speed up Class::Accessor::Grouped.
• on Perl 5.8, install Class::C3::XS.
• prefetch relationships, where possible. see "Using joins and prefetch".
• use populate in void context to insert data when you don't need the resulting result objects, if possible — but see the caveats 👀

when inserting many rows, for best results, populate a large number of rows at a time, but not so large that the table is locked for an unacceptably long time.

if using create instead, use a transaction and commit every "X" rows; where "X" gives you the best performance without locking the table for too long.

• when selecting many rows, if you don't need full-blown DBIx::Class::Row objects, consider using DBIx::Class::ResultClass::HashRefInflator.
• see also "STARTUP SPEED" and "MEMORY USAGE" in this document.

---

⚡ STARTUP SPEED ⚡

DBIx::Class programs can have a significant startup delay because the ORM loads all the relevant classes 😩 this section examines techniques for reducing that startup delay.

these tips are listed in order of decreasing effectiveness — so the first tip, if applicable, should have the greatest effect on your application. periodt.

🗿 Statically Define Your Schema

if you're using DBIx::Class::Schema::Loader to build the classes dynamically based on the database schema, then there will be a significant startup delay. facts.

for production, use a statically defined schema (which can be generated using DBIx::Class::Schema::Loader to dump the database schema once — see make_schema_at and dump_directory for more details on creating static schemas from a database).

🧬 Move Common Startup into a Base Class

typically DBIx::Class result classes start off with:

use base qw/DBIx::Class::Core/;
__PACKAGE__->load_components(qw/InflateColumn::DateTime/);

so if this preamble is moved into a common base class:

package MyDBICbase;

use base qw/DBIx::Class::Core/;
__PACKAGE__->load_components(qw/InflateColumn::DateTime/);
1;

and each result class then uses this as a base:

use base qw/MyDBICbase/;

then the load_components is only performed once — which can result in a considerable startup speedup for schemas with many classes 🎀

📋 Explicitly List Schema Result Classes

the schema class will normally contain:

__PACKAGE__->load_classes();

to load the result classes. this will use Module::Find to find and load the appropriate modules. explicitly defining the classes you wish to load will remove the overhead of Module::Find and the related directory operations:

__PACKAGE__->load_classes(qw/ CD Artist Track /);

if you're instead using the load_namespaces syntax to load the appropriate classes, there is not a direct alternative avoiding Module::Find. sorry bestie 💀

---

🧠 MEMORY USAGE 🧠

🗃️ Cached statements

DBIx::Class normally caches all statements with prepare_cached(). this is normally a good idea, but if too many statements are cached, the database may use too much memory and may eventually run out and fail entirely 😭 if you suspect this may be the case, you may want to examine DBI's CachedKids hash:

# print all currently cached prepared statements
print for keys %{$schema->storage->dbh->{CachedKids}};
# get a count of currently cached prepared statements
my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};

if it's appropriate, you can simply clear these statements, automatically deallocating them in the database:

my $kids = $schema->storage->dbh->{CachedKids};
delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;

but what you probably want is to expire unused statements and not those that are used frequently. you can accomplish this with Tie::Cache or Tie::Cache::LRU:

use Tie::Cache;
use DB::Main;
my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
    on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },
});

---

❓ FURTHER QUESTIONS? ❓

check the list of additional DBIC resources 🫶

---

📜 COPYRIGHT AND LICENSE 📜

this module is free software copyright by the DBIx::Class (DBIC) authors. you can redistribute it and/or modify it under the same terms as the DBIx::Class library 💖

---

and that's a wrap on the whole cookbook, bestie!! 🎉✨ this was perl v5.42.0, dated 2025-01-22, and you just finished DBIx::C...Cookbook(3) — go forth and slay your queries 👑💅🌸