Hi,

I am quite new to DBIx::Class and would like to use DBIx::Class::Schema::Loader to retrieve information about table constraints. I must admit being a bit lost in the documentation for DBIx::Class. I have played around a bit using an SQLite database and found a way how one can get part of the information as follows:

package My::Schema;

use strict;
use warnings;

use DBIx::Class::Schema::Loader qw/ make_schema_at /;

my $dsn = 'dbi:SQLite:./testdb';

make_schema_at(
    'My::Schema',
    {   debug          => 0,
        dump_directory => './lib',
    },
    [ $dsn, '', '' ],
);

my $schema = My::Schema->connect( $dsn, '', '', '' );

my @relationships = $schema->source('T')->_relationships();

#...

1;
[download]

when tested against a SQLite database containing the following three tables:

CREATE TABLE a (u integer, PRIMARY KEY (u));
CREATE TABLE t (i integer, j integer, u integer, Primary key (i,j), co
+nstraint fkey1 foreign key (u) references a (u));
CREATE TABLE s (j integer, r1 integer, r2 integer, constraint fkey for
+eign key (r1,r2) references t (i,j));
[download]

the debugger output shows the following for the array @relationships:

  DB<2> x @relationships
0  HASH(0x261359c)
   'ss' => HASH(0x3c6eef4)
      'attrs' => HASH(0x3c6c884)
         'accessor' => 'multi'
         'cascade_copy' => 0
         'cascade_delete' => 0
         'join_type' => 'LEFT'
      'class' => 'My::Schema::Result::S'
      'cond' => HASH(0x3c6926c)
         'foreign.r1' => 'self.i'
         'foreign.r2' => 'self.j'
      'source' => 'My::Schema::Result::S'
   'u' => HASH(0x3bfe16c)
      'attrs' => HASH(0x3bfb69c)
         'accessor' => 'filter'
         'is_deferrable' => 0
         'is_foreign_key_constraint' => 1
         'join_type' => 'LEFT'
         'on_delete' => 'NO ACTION'
         'on_update' => 'NO ACTION'
         'undef_on_null_fk' => 1
      'class' => 'My::Schema::Result::A'
      'cond' => HASH(0x3bfdd8c)
         'foreign.u' => 'self.u'
      'source' => 'My::Schema::Result::A'
[download]

So it contains a lot of the information I am looking for. But apart from the fact that _relationships() starts with an underscore I am quite sure that rummaging about the innards of this data structure is not the right way to do it.

Is there a better way?

Update: I did not say exactly what information I am looking for, which is: for a specific table, I need the unique constraints/indices together with the constrained columns' names as well as all the foreign keys with constrained columns, referenced tables and referenced columns.