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DBIx::Class::Manual::Cookbook - レシピいろいろ

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ページ処理された結果¶

結果セットが膨大になりそうなら、ページ処理された結果をDBIx::Classで取得できます。 一回に、決まった数のレコードしかとってきません:

   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

上のケースのいずれでも、結果セットに、Data::Pageオブジェクト(テンプレートに使うのに適した) を得ることができます。pagerメソッドを使って:

  return $rs->pager();

複雑な WHERE節¶

特定の演算子を使ったクエリを定式化する必要がある時もあるでしょう:

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

結果は下記のWHERE節のようなものになります:

  WHERE artist LIKE ? AND title LIKE ?

そして、プレースフォルダーのために、バインドする値を続けます: %Lamb%, '%Fear of Fours%'.

もうちょっと複雑なロジックが必要な他のクエリもあるでしょう:

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

結果は下記のWHERE節になります:

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

複雑なクエリをつくるためのより詳しい説明は、"WHERE CLAUSES" in SQL::Abstractを見てください。

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');

  # ->table, ->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", "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]) }

特定のカラムを使う¶

テーブルから特定のカラムが欲しいだけのときには、columnsを使って、 必要なものを指定できます。何にも使わない大量のデータを取り込むのを 避けることができます。

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

  # Equivalent SQL:
  # SELECT artist.name FROM artist

後でも見ますが、これは、selectとasのショートカットです。 columnsはselectとasと一緒には使えません。

データベースの関数やストアドプロシージャを使う¶

selectとasの組み合わせで、カラムの値としてデータベース関数やストアド プロシージャの結果を返すのに使うことが出来ます。selectを使って、カラムの 値のためのソースを指定できます(例えば、カラム名、関数、ストアドプロシージャ名)。 それから、asを、返された値にアクセスするのに使うカラム名をセットするのに 使えます:

  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

as 属性は、SQLのシンタックス SELECT foo AS barとまったく関係ないことに 気をつけてください("ATTRIBUTES" in DBIx::Class::ResultSetのドキュメントを見てください)。 ベースクラスにカラムとしてエイリアスがある(すなわち、add_columnsで追加されている)のなら、 普通にそれにアクセスできます。この例で言えば、Artistクラスには、 nameカラムがあるので、nameアクセサを使えます:

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

一方で、エイリアスが既存のカラムに一致しないなら、get_columnアクセサを使って、 値を取得する必要があります:

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

get_columnが気に入らなければ、いつでも、下記のいずれかを使ってどんな エイリアスにもアクセサを作れます:

  # 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:

結果のグルーピング¶

DBIx::Class supports GROUP BY as follows:

DBIx::ClassはGROUP BYをサポートします:

  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

上記の( join 、 select 、 as 、 group_by)属性の使い方がわからなければ、 "ATTRIBUTES" in DBIx::Class::ResultSetドキュメントをみてください。

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 => 'inner' }
      )->get_column('year')->max_rs->as_query,
    },
  });

That creates the following SQL:

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

定義済み検索¶

DBIx::Class::ResultSetクラスを継承して、自分自身のクラスを書き、よく使う 検索をメソッドとして定義できます:

  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, simply place the file into the ResultSet directory next to your Result directory, and it will be automatically loaded.

自分の結果セット使うには、最初に、自分のMy::DBIC::Schema::CDクラスの中で、 DBIx::Classにそのインスタンスを作るように教えます。

  # 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.

それから、コードの中で、新しいメソッドを呼びます:

   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.) However, it can be accomplished with DBIx::Class when necessary by resorting to literal SQL:

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

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

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

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

Note: the plain_value string in the [ plain_value => 1979 ] part should be either the same as the name of the column (do this if the type of the return value of the function is the same as the type of the column) or in the case of a function it's currently treated as a dummy string (it is a good idea to use plain_value or something similar to convey intent). The value is currently only significant when handling special column types (BLOBs, arrays, etc.), but this may change in the future.

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

JOINS AND PREFETCHING¶

joins と prefetch を使う¶

join属性を使って、関連するテーブルの1つ以上のカラムを使って、 検索や、結果のソートができます。

This requires that you have defined the DBIx::Class::Relationship. For example :

DBIx::Class::Relationshipを定義する必要があります。例えば:

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

特定のアーティスト名の全てのCDを返すためには:

  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'

In that example both the join, and the condition use the relationship name rather than the table name (see DBIx::Class::Manual::Joining for more details on aliasing ).

必要なら、order_by属性にそれを含めて、関連するテーブルのいずれかのカラムで ソートすることも出来ます(テーブル名ではなくエイリアスのリレーション名を再度使って):

  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

join属性は関連するテーブルのカラムを使って検索やソートをする必要があるときにのみ 使われるべきだということに注意してください。 メインのテーブルからカラムが必要なときに、関連するテーブルを結合するのは、 パフォーマンスが悪いです!

で、、CDのリストを、それぞれのアーティストの名前と一緒に表示したいとしましょう。 下記のやりかたでうまくいきます:

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

ですが、一つ問題があります。このメインクエリで、cdとartistテーブルの両方を 検索していますが、cdからのみデータが返されています。返されたCDオブジェクトの一部で、 アーティスト名を得るために、DBIx::Classは、データベースに戻ります:

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

上記のようなステートメントが、メインクエリによって返された、それぞれの、全ての CDで走ります。5つのCDであれば、5つの別のクエリです。100のCDであれば、100の別の クエリ!

ありがたいことに、DBIx::Classは、prefetch属性があり、この問題を解決できます。 この属性を使うと、先に関連するテーブルから結果をとってこれます:

  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

CDのリストを表示するコードは同じ物が使えます:

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

DBIx::Classはartistテーブルからすべてのマッチするデータを先にとってきています。 そのため、余分なSQLステートメントは実行されません。より効率的なクエリになりました。

また、prefetchは、関連するテーブルからデータを必ず使うとわかっているときのみに、 使うべきです。メインテーブルからのカラムしか必要としないなら、 関連するテーブルから先に取得するのは、パフォーマンスを悪くします!

複数の結合(join)¶

In the examples above, the join attribute was a scalar. If you pass an array reference instead, you can join to multiple tables. In this example, we want to 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'
  # ORDER BY artist.name

マルチステップの結合(join)¶

2つ以上の深いリレーションシップでjoinしたいときもあるでしょう。 この例では、LinerNotesに特定の文字が含まれるCDを持っている、 Artistオブジェクトを探したいとします:

  # 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%'

結合は任意のレベルでネストできます。ですので、後から、ライナーノーツを 誰が書いたかを元に、返されるアーティストの数を減らしたいと決めたとしたら:

  # 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'

マルチステップで複数の結合¶

With various combinations of array and hash references, you can join tables in any combination you desire. 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は、マルチステップの結合と同じシンタックスで、 2つ以上の深いリレーションシップでネストできました:

  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

これで、cdとartistのリレーションシップにアクセスするのに、 追加のSQLステートメントは必要ありません:

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

ROW-LEVEL OPERATIONS¶

列オブジェクトのスキーマを得る¶

次のようにして、列のオブジェクトからスキーマを得ることができます:

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

全てのメソッドで、スキーマオブジェクトを順に回したくなければ、便利でしょう。

最後にデータベースにインサートしたプライマリキーの値を取りたい¶

last_insert_id を取るともいいます。

コアコンポーネントのPK::Autoに感謝して、直接:

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

オートインクリメントのプライマリキーを使っていないのなら、おそらく動きません。 ですが、その場合は、すでに、プライマリキーの値を知っていることでしょう。

Stringification¶

overload モジュールで標準的な文字列化のテクニックを使えます。

ひとつのカラムについて、オブジェクト自身を文字列化するには、 次のようにします。(カラム/メソッドでnameを置き換えてください)

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

より複雑な文字列化では、無名サブルーチンを使えます:

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

文字列化の例¶

二つのテーブルがあるとします:ProductとCateogry。 テーブルの定義は次の通り:

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

categoryはCategoryテーブルの外部キーです。

Productオブジェクト$objがあり、次のように書いたとすると、

  print $obj->category

期待どおりには動きません。

カテゴリの内容を得たいなら、例えば、Categoryテーブルのクラス定義に次の メソッドを追加すべきです:

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

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

find_or_create が見付けたのか、列を作ったのかを知りたい？¶

find_or_newを代わりに使ってください。それから、in_storageをチェックします:

  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
  }

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;

DBIx::Classのプロキシクラスを動的にサブクラス化する¶

AKA 1つのテーブルからマルチクラスのオブジェクトに展開する

DBIx::Classクラスはプロキシクラスです。そのため、基本的なサブクラス化以上に、 いくつかの違ったテクニックが必要とされます。 この例では、管理者用に真偽値を持っているユーザーテーブルがあります。 管理者ユーザーには、オブジェクト(DBIx::Class::Row)のメソッドを、 普通のユーザーと同じようにあたえますが、管理者のみの特別なメソッドも、 あたえたいとします。このために2つのプロキシクラスファイルに分割するのは 理にかないません。Adminクラスに全てのユーザークラスのメソッドをコピー することになります。これをするために、よりすっきりした方法があります。

ユーザーのプロキシクラス内でinflate_resultメソッドをオーバーライドすることで、 望んでいる効果が得られます。このメソッドは、ストレージから結果が展開されるときに、 DBIx::Class::ResultSetによって呼ばれます。 返されたオブジェクトを掴んだら、探している値を調べ、管理者オブジェクトであれば、 それをblessして返します。下の例を見てください:

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.

高速に結果を得るために、オブジェクトの作成をスキップしたい¶

DBIx::Class はスピードのためには作られておらず、DBIx::Classは、 利便性と使い易さのために作られました。ですが、時には、データをただ 取得しなければいけないだけの時があり、素敵なオブジェクトはスキップ したい場合もあるでしょう。

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

この用途には、DBIx::Class::ResultClass::HashRefInflatorが、簡単に使えます。

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

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

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

Wasn't that easy?

Beware, 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.

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).

RESULTSET OPERATIONS¶

Getting Schema from a ResultSet¶

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

 $rs->result_source->schema

Getting Columns Of Data¶

AKA Aggregating Data

特定のカラムの合計を探したければ、いくつもの方法があります。自明のものとしては、 searchを使うものです:

  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');

もしくは、DBIx::Class::ResultSetColumnを使うことも出来ます。 これは、ResultSetでget_columnを使ってカラムを取るときに 返されるものが取れます。

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

これを、次のようにできます:

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

または、このカラムの値のみを通してイテレートします:

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

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

ResultSetColumnは少しだけビルトインの関数があります。 これにないものが必要なら、funcメソッドを代わりに使うことができます:

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

こうすると、下記のSQLステートメントが走ります:

  SELECT AVERAGE(Cost) FROM Items me

もちろん、使っているデータベースがこの関数をサポートしていなければいけません。 より詳しくは、DBIx::Class::ResultSetColumnをみてください。

Creating a result set from a set of rows¶

Sometimes you have a (set of) row 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;

リレーションシップを使う¶

関連するテーブルに新しい列を作る¶

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

関連するテーブルを検索する¶

$autorの著者で、'Titanic'という名前の本だけを検索したい。

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

関連するテーブルのデータを削除する¶

$autorの著者で、Titanicという名前の本だけを削除したい。

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

関係する結果セットの順序付け¶

順序付けられた関係が常にほしいなら、リレーションシップを作るときに、次の指定をできます。

page_numberを降順で、$book->pagesを並び変えたいなら。次のように リレーションを作ります:

  __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 add to $attr as follows:

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

Many-to-many のリレーションシップ¶

これは、単純にManyToManyを使います:

  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 MyDatabase::Main::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' => 'MyDatabase::Main::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 MyDatabase::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 overridding 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
    = MyDatabase::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.

txn_do でのトランザクション¶

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:

0.04001以降に、 DBIx::Class::Storage::DBIとDBIx::Class::Schemaに、改良された トランザクションサポートがあります。これを使う推奨される方法の一例です:

  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.

ネストされたトランザクションは期待どおりに動きます。 一番外側のトランザクションだけが実際に$dbhにコミットを発行します。 どのレベルのどのトランザクションでも、ロールバックしたら、 ネストされたトランザクション全てが失敗します。

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 happend, 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 ($caught) {
    # 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 that 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.

The recommend way of achieving this is to use the make_schema_at method:

  perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
    -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'

This will create a tree of files rooted at ./lib/My/Schema/ containing source definitions for all the tables found in the foo database.

Creating DDL SQL¶

The following functionality requires you to have SQL::Translator (also known as "SQL Fairy") installed.

To create a set of database-specific .sql files for the above schema:

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

By default this will create schema files in the current directory, for MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.

To create a new database using the schema:

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

To import created .sql files using the mysql client:

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

To create ALTER TABLE conversion scripts to update a database to a newer version of your schema at a later point, first set a new $VERSION in your Schema file, then:

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

This will produce new database-specific .sql files for the new version of the schema, plus scripts to convert from version 0.1 to 0.2. This requires that the files for 0.1 as created above are available in the given directory to diff against.

Select from dual¶

Dummy tables are needed by some databases to allow calling functions or expressions that aren't based on table content, for examples of how this applies to various database types, see: http://troels.arvin.dk/db/rdbms/#other-dummy_table.

Note: If you're using Oracles dual table don't ever do anything other than a select, if you CRUD on your dual table you *will* break your database.

Make a table class as 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 you've loaded your table class select from it using select and as instead of columns

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

All you have to do now is be careful how you access your resultset, the below will not work because there is 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.

You could of course 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";
  }

In case you're going to use this "trick" together with "deploy" in DBIx::Class::Schema or "create_ddl_dir" in DBIx::Class::Schema a table called "dual" will be created in your current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or "sequence.nextval" anymore from dual. To avoid this problem, just tell SQL::Translator to not 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";
  }

Here are some example select conditions to illustrate the different syntax you could use for doing stuff like oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')

  # 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¶

Often you will want indexes on columns on your table to speed up searching. To do this, create a method called sqlt_deploy_hook in the relevant source class (refer to the advanced callback system if you wish to share a hook between multiple sources):

 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 change the index depending on the type of the database for which SQL is being generated:

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

You can also add hooks to the schema level to stop certain tables being created:

 package My::Schema;

 ...

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

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

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.

スキーマのバージョニング¶

下記の例では、DBIx::Classを使って、顧客向けにバージョン付きのスキーマをどうやって デプロイするかをお見せします。基本的なプロセスは下記のようになります:

1. Create a DBIx::Class schema

   DBIx::Classスキーマを作ります

2. Save the schema

   スキーマを保存します

3. Deploy to customers

   顧客にデプロイします

4. Modify schema to change functionality

   スキーマを変更して、 functionality を変更します

5. Deploy update to customers

   顧客に更新をデプロイします

DBIx::Calssスキーマを作る

これは、手で行うことも、既存のデータベースからスキーマを作るで説明しますが、 既存のデータベースから生成することもできます。

スキーマを保存する

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

顧客にデプロイする

スキーマをデプロイするのには複数の方法があります。 このレシピの範疇を越えそうですが、含めておきます:

1. Require customer to apply manually using their RDBMS.

   顧客にRDBMSを使って、手で適用するように求める

2. Package along with your app, making database dump/schema update/tests all part of your install.

   アプリケーションと一緒に、データベースのダンプ、スキーマのアップデート、 インストールの全パートのテストを作るように、パッケージする

機能性を変更するために、スキーマを変更する

アプリケーションが進化するにつれ、機能性を変更するために、スキーマを修正する必要があるでしょう。 DBIx::Classでスキーマを変更したら、以前のように修正されたスキーマをエクスポートし、 "Creating DDL SQL"にあるような変換スクリプトを使います

Deploy update to customers

顧客に更新をデプロイします

Add the DBIx::Class::Schema::Versioned schema component to your Schema class. This will add a new table to your database called dbix_class_schema_vesion which will keep track of which version is installed and warn if the user tries to run a newer schema version than the database thinks it has.

Alternatively, you can send the conversion SQL scripts to your customers as above.

生成されたSQLをクォートする¶

データベースにスペースおよび/または予約語のついたカラム名がある場合、 SQLクエリ内で、クォートされる必要があります。次のようにします:

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

1行目は、クォート文字をセットしています。ブラケットのペアか、", 'です。

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

正しいクォート文字を使うために、データベースのドキュメントをチェックしてください。 name_sepは、SQLジェネレーターが正しい場所にクォートを置くために、 セットしなければいけません。デフォルトでは.になります。

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

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

In some cases, quoting will be required for all users of a schema. To enforce this, 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]
  });

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

In conditions (e.g. \%cond in the "search" in DBIx::Class::ResultSet family of methods) you cannot directly use array references (since this is interpreted as a list of values to be ORed), but you can use the following syntax to force passing them as bind values:

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

See "array_datatypes" in SQL::Abstract and "Literal SQL with placeholders and bind values (subqueries)" in SQL::Abstract for more explanation. Note that DBIx::Class sets "bindtype" in SQL::Abstract to columns, so you must pass the bind values (the [1, 2, 3] arrayref in the above example) wrapped in arrayrefs together with the column name, like this: [column_name => value].

Formatting DateTime objects in queries¶

To ensure WHERE conditions containing DateTime arguments are properly formatted to be understood by your RDBMS, you must use the DateTime formatter returned by "datetime_parser" in DBIx::Class::Storage::DBI to format any DateTime objects you pass to search conditions. Any Storage object attached to your Schema provides a correct DateTime formatter, so all you have to 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),
        ],
      }
    },
  );

Without doing this the query will contain the simple stringification of the DateTime object, which almost never matches the RDBMS expectations.

This kludge is necessary only for conditions passed to "search" in DBIx::Class::ResultSet, whereas create, find, "update" in DBIx::Class::Row (but not "update" in DBIx::Class::ResultSet) are all DBIx::Class::InflateColumn-aware and will do the right thing when supplied an inflated DateTime object.

Using Unicode¶

When using unicode character data there are two alternatives - either your database supports unicode characters (including setting the utf8 flag on the returned string), or you need to encode/decode data appropriately each time a string field is inserted into or retrieved from the database. It is better to avoid encoding/decoding data and to use your database's own unicode capabilities if at all possible.

The DBIx::Class::UTF8Columns component handles storing selected unicode columns in a database that does not directly support unicode. If used with a database that does correctly handle unicode then strange and unexpected data corrupt will occur.

The Catalyst Wiki Unicode page at http://wiki.catalystframework.org/wiki/tutorialsandhowtos/using_unicode has additional information on the use of Unicode with Catalyst and DBIx::Class.

The following databases do correctly handle unicode data:-

MySQL¶

MySQL supports unicode, and will correctly flag utf8 data from the database if the 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 set, a data retrieved from a textual column type (char, varchar, etc) will have the UTF-8 flag turned on if necessary. This enables character semantics on that string. You will also need to ensure that your database / table / column is configured to use UTF8. See Chapter 10 of the mysql manual for details.

See DBD::mysql for further details.

Oracle¶

Information about Oracle support for unicode can be found in "Unicode" in DBD::Oracle.

PostgreSQL¶

PostgreSQL supports unicode if the character set is correctly set at database creation time. Additionally the pg_enable_utf8 should be set to ensure 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¶

クラスベースからスキーマベースセットアップへの簡単な移行¶

DBIx::Classへのスキーマベースのアプローチを使いたい(SchemaIntro.podをみてください)、 でも、既存の大量のクラスで、従来のクラスベースのセットアップがあり、 手でそれらを動かしたくはないとします。手で動かす変わりに、下記の気の利いたスクリプトを 試してみて下さい:

  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;

Module::Findを使って、MyDB::*名前空間にある全てのサブクラスを探すことが出来ますが、 これは、今のところ、読者への課題としておきます。

メソッドのオーバーロード¶

DBIx::ClassはClass::C3パッケージを使っています。Class::C3はメソッドコールを 再分岐させるために使われています。メソッドをオーバーロードするために、 next::methodの呼び出しを使わなければいけません。 DBIx::ClassとClass::C3の利用に関する詳しい情報は、 DBIx::Class::Manual::Componentを見てください。

列のデフォルトの値を用意する¶

単純に、newメソッドをオーバーライドします。 next::methodの使いかたに注意してください。

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

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

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

    return $new;
  }

next::methodについてより詳しくは、Class::C3のドキュメントを参照してください。 これをするための、自分自身のベースクラスを書くための、より多くの方法については、 DBIx::CLass::Manual::Componentを見てください。

DBIx::Classで"triggers"をする方法を探している人も、これを探しているでしょう。

他が変更されたらいつでもあるフィールドを変更する¶

例えば、3つのカラムがあったとします。id、number、squared。 numberに変更を加え、squaredは自動的に、numberの二乗の値を セットしたいとします。numberアクセサをClass::Method::Modifiersで ラップすることで、これができます:

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

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

    $self->next::method(@_);
  }

next::methodを呼び出すことで、大変な仕事がされていることに注意しましょう。 呼び出しが、(複数の)スーパークラスのstore_columnに再分岐されてます:

Generally, if this is a calculation your database can easily do, try and avoid storing the calculated value, it is safer to calculate when needed, than rely on the data being in sync.

関連するオブジェクトを自動的に作る¶

多くのCDを持ったArtistクラスがあるとします。 さらに、Artistオブジェクトをインサートする度毎にCDオブジェクトを 作りたいとします。これは、オブジェクトのinsertをオーバロードすればできます:

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

If you want to wrap the two inserts in a transaction (for consistency, an excellent idea), 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
  }

カラムのアクセサをラッピング/オーバーロードする¶

Problem:

問題:

 "Camera"テーブルがあったとして、それぞれのカメラについて、
説明を関連付けたいとします。ほとんどのカメラでは、他のカラムから説明を生成できるでしょう。
しかし、特別な数ケースでは、カメラのカスタムの説明を関連付けたいとします。

Solution:

解:

データベーススキーマで、"Camera"にdescriptionフィールドが定義し、 textとnullの値を含むことをできるようにします。

DBICは、カスタムの description が定義されていなければ、 提供されているまともなデフォルトのカラムアクセサをオーバーロードできます。 フィールドがnullかnullでないかに依存して、アクセサはdescriptionを返すか生成します。

まず、"Camera"スキーマクラスで、下記のようにdescriptionフィールドを定義します:

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

次に、アクセサラッパーサブルーチンを定義します:

  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;
  }

デバッギングとプロファイリング¶

Data::Dumperと、DBIx::Classオブジェクト¶

Data::Dumper はデバッグにとても便利なツールです。ですが、 生成された全てのデータの中の、該当のデータを見付けるのが難しい時があります。 特に、次のように単純に使おうとしたら、

  use Data::Dumper;

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

複数ページにわたり、CDオブジェクトのスキーマと結果のソースが、複数 ページにわたるデータとなってスクリーンにダンプされます。ですが、 普通はオブジェクトの数カラムの値の1つのみに興味があるので、これでは、 あまり便利ではありません。

幸運にも、Data::Dumperが出力する前にデータを加工することが出来ます。 簡単にフックを定義すると、Data::Dumperがダンプする前に、オブジェクトで それを呼び出します。

  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

スキーマの構造が、全てのテーブルクラスのための共通のベースクラスがあるような ものであれば、単純に、ベースクラスに、_dumper_hookと同じようなメソッドを作り、 $Data::Dumper::Freezerにその名前をセットします。 Data::Dumperは、自動的に、データを出力する前に、きれいにします。 "EXAMPLES" in Data::Dumperにより詳しい情報ががあります。

プロファイリング¶

DBIx::Class::Storageのデバッギングを有効にすれば、 実行されたSQLだけでなく、クエリの完了や、トランザクションの開始/コミット も、出力します。SQLを分析したければ、 DBIx::Class::Storage::Statistics クラスのサブクラスを作り、自分自身のプロファイリングメカニズムを書けます:

  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;

You can then install that class as the debugging object:

それから、このクラスを、デバッギングオブジェクトにインストールできます:

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

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

より複雑な例としては、配列に実行する各SQLを貯めておくようなものを含むでしょう:

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

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

それから、SQLステートメントの平均、最長、最短実行時間を取れますし、ある パラメータが異常な振る舞いを引き起こしていれば、掘り下げることも出来るでしょう。 DBIx::Class::QueryLogもチェックしたいいかもしれません。

IMPROVING PERFORMANCE¶

• 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 DBIx::Class::Row 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 as the ORM loads all the relevant classes. This section examines techniques for reducing the startup delay.

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

Statically Define Your Schema¶

If you are using DBIx::Class::Schema::Loader to build the classes dynamically based on the database schema then there will be a significant startup delay.

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/);

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 are instead using the load_namespaces syntax to load the appropriate classes there is not a direct alternative avoiding Module::Find.

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 },
    });

翻訳について¶

翻訳者：加藤敦 (ktat.is at gmail.com)

Perlドキュメント日本語訳 Project にて、 Perlモジュール、ドキュメントの翻訳を行っております。

 http://perldocjp.sourceforge.jp/
 http://sourceforge.jp/projects/perldocjp/
 http://www.freeml.com/perldocjp/
 http://www.perldoc.jp