Is it possible to create composite Primary Keys in Records?

Question

I've structured my Record as such:

<?php
namespace Craft;

class MyPlugin_MerchantOrderRecord extends BaseRecord
{
  public function getTableName()
  {
    return 'myplugin_merchant_orders';
  }

  protected function defineAttributes()
  {
    return [
      'merchant_id' => AttributeType::Number,
      'order_id' => AttributeType::Number,
      ...
    ];
  }

  public function primaryKey()
  {
    return ['merchant_id', 'order_id'];
  }

  public function defineRelations()
  {
      return [
        'merchant' => [static::BELONGS_TO, 'MyPlugin_MerchantRecord', 'merchant_id', 
               'required' => true, 'onDelete' => static::CASCADE],
        'order' => [static::BELONGS_TO, 'Commerce_OrderRecord', 'order_id', 
               'required' => true, 'onDelete' => static::CASCADE],
      ];
  }
}

When I install the plugin I get the following error:

Illegal offset type in isset or empty

If I take away the primaryKey() definition, the table is created successfully and the foreign keys are in place as expected.

Any help gratefully received.

Answer 1

This should be fixed in the next (post 2.6.2791) release so that plugins can define composite primary keys in their records.

Answer 2

It would appear not unfortunately.

Craft's BaseRecord (which a Record should inherit from) tries to uses the primaryKey() method call to help create the table, but assumes a single column name is returned, not an Array and so falls over on the isset call.

$pk = $this->primaryKey();

if (isset($columns[$pk]))
{
  $columns[$pk]['primaryKey'] = true;
  $addIdColumn = false;
}
else
{
  $addIdColumn = true;
}

I'm guessing it should work because the CActiveRecord (which the BaseRecord inherits from) states in it's comments for PrimaryKey:

@return mixed the primary key of the associated database table.

If the key is a composite one consisting of several columns, it should
return the array of the key column names.

EDIT: In the end I added the following to my Plugin file, and that seemed to do the trick:

public function onAfterInstall()
{
  craft()->db->createCommand()->dropColumn('myplugin_merchant_order', 'id');
  craft()->db->createCommand()->addPrimaryKey('myplugin_merchant_order', ['merchant_id', 'order_id']);
}

I also had to add this to my Record, to stop the validation failing because I'd removed the id column in the above step:

public function primaryKey()
{
    return null;
}