DBIx and inheritance in Perl

I'm currently trying to implement the following scenario with DBIx:

The table products contains "general products" and "bundle products" (bundle products are collections of general products):

package Product;
use base 'DBIx::Class::Core';
__PACKAGE__->table("products");
__PACKAGE__->add_columns(
  "productId",
  { data_type => "varchar", is_nullable => 0, size => 10},
  "name",
  { data_type => "varchar", is_nullable => 1, size => 150},
  "type",
  {
     data_type => "enum",
     default_value => "general",
     extra => {
       list => ["general", "bundle"],
     },
     is_nullable => 0,
  });

As you can see, wether the product is a general product or a bundle product is saved in the column type .

Now I would like to encapsulate this information in the class identity: I would like to have following classes:

Product ( type does not matter)

BundleProduct ( type = 'bundle')

GeneralProduct ( type = 'general')

I wrote:

package BundleProduct;
use base 'Product';

__PACKAGE__->resultset_attributes({ where => { 'type' => 'bundle' } });
1;

and

package GeneralProduct;
use base 'Product';

__PACKAGE__->resultset_attributes({ where => { 'type' => 'general' } });
1;

But when executing

my @allProducts = $schema->resultset('BundleProduct')->all;

all general products are fetched. Although the resulting objects are of instance BundleProduct , the generated SQL contains the WHERE-condition of the class GeneralProduct ( type = 'general'). Even worse: If I try to fetch a Product (base class of BundleProduct and GeneralProduct ) the condition type = 'general' is applied, too! It seems that the definition within GeneralProduct overwrites all other definitions.

What is wrong with my design?

---

The usage of resultset_attributes is not recommended. You should implement a result set class for Product with methods bundle_products and general_products :

package My::Schema::ResultSet::Product;
use base 'DBIx::Class::ResultSet';

sub bundle_products  { shift->search({ type => 'bundle' }); }
sub general_products { shift->search({ type => 'general' }); }

Then you can search specific products like this:

$schema->resultset('Product')->bundle_products->all;
$schema->resultset('Product')->general_products->all;

See the documentation of resultset_attributes.

Also have a look at DBIx::Class::DynamicSubclass. It adds some useful features when subclassing results.

---

This might be slightly OT, but I seem to always run into some insidious application implementation problem when dealing with enum data types in my schemas.

So I don't use them any more. I use foreign key relationships and either individual tables or a combined table holding all codes:

<id, code_type, code_name> 
< 1, 'product_type', 'bundle'>
< 2, 'product_type', 'general'>

and then I join from product to product_type on product.product_type_id = code_table.id

This technique has made application implementation much, much easier at the cost of some additional database management in the beginning of the project.

---

It may always be defaulting to general because the data is not being inflated to an Enum object?

Surprised that it doesn't give a clear error but perhaps adding below (to Product package) will fix your problem:

__PACKAGE__->load_components(qw/InflateColumn::Object::Enum/);

Additional to above also try adding is_enum => 1 to your type column definition:

type => {
  data_type     => "enum",
  is_enum       => 1,  
  default_value => "general",
  is_nullable   => 0,
  extra => {
    list => ["general", "bundle"],
  },
},

NB. This should enforce the use of the inflation object ( Object::Enum ) whereas without it I believe it tries to use the enum native to the RDBMS you're using (if its present).

Fingers crossed this works. If not try removing the default_value to see how this affects things.

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