如何使用固定连接条件建立DBIx :: Class关系？

cpan install DBIx::Class

package MyApp::Schema;

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

__PACKAGE__->load_classes(qw/
    User
    Post
/);

1;

package MyApp::Schema::User;

use strict;
use warnings;
use base 'DBIx::Class';

__PACKAGE__->load_components(qw/
    Core
    InflateColumn::DateTime
/);

__PACKAGE__->table('users');

__PACKAGE__->add_columns(qw/
    id
    name
    email
/);

__PACKAGE__->set_primary_key('id');

__PACKAGE__->has_many(
    'posts',
    'MyApp::Schema::Post',
    { 'foreign.user_id' => 'self.id' },
);

1;

my $users = $schema->resultset('User')->search({ email => 'example@example.com' });
my $posts = $users->related_resultset('posts');