Perl DBIx::Class - Is it possible to provide a default value for inserting by using column attributes

Question

I have a (MySQL) table, import , defined as:

CREATE TABLE `import` (
  `importId` varchar(36) COLLATE utf8mb4_unicode_ci NOT NULL,
  `stuff`    varchar(12) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`importId`),
  KEY `stuff` (`stuff`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

I have used DBIx::Class::Schema::Loader->make_schema_at to generate my DBIx::Class schema.

I want to be able to issue $schema->resultset('Import')->create({}); (ie, not providing a primary key) and have the importId field automatically populated with the result of a call to MySQL's uuid() function. To attempt to do this, I added the following to the bottom of Schema/Result/Import.pm :

# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:cKY/6hdjrNaMgdhm6SlzoQ

use Data::Dumper;
print Dumper __PACKAGE__->columns_info();

__PACKAGE__->add_columns(
    '+importId' =>
    {
        default_value => \'uuid()',                              #'
    },
);

print Dumper __PACKAGE__->columns_info();

The data dumps show that the default_value attribute was added to importId, as expected:

$VAR1 = { 
      'importId' => { 
                      'data_type' => 'varchar',
                      'default_value' => \'uuid()',              #'
                      'is_nullable' => 0,
                      'size' => 36,
                      'accessor' => 'import_id'
                    },
      'stuff' => { 
                   'data_type' => 'varchar',
                   'is_nullable' => 1,
                   'size' => 12
                 }
};

But if I don't provide a value for importId in a create() call, DBIx::Class still issues INSERT INTO import () VALUES () .

I did achieve what I wanted by modifying the insert() method by placing the following at the end of Schema/Result/Import.pm :

use Moo;

before 'insert' => sub
{   
    my $self = $_[0];
    my $column_data = $self->{_column_data};
    $column_data->{importId} = \'uuid()'                         #'
        unless exists $column_data->{importId} && defined $column_data->{importId};
};

I had thought I should be able to achieve this with the default_value column attribute. Am I misunderstanding how this attribute works, or have I just implemented it incorrectly?

Answer 1

You have to read docs better.

Look into L<DBIx::Class::ResultSource/add_columns> for default_value and you will find that

 default_value 

Set this to the default value which will be inserted into a column by the database. Can contain either a value or a function (use a reference to a scalar eg \\'now()' if you want a function). This is currently only used to create tables from your schema, see "deploy" in DBIx::Class::Schema.

So, if you don't use deployment via DBIC, you rather want to add DEFAULT uuid() into your SQL schema for corresponded column.