How do I programmatically create an entity reference in hook_entity_info()?

Question

Is there a way to create an entity reference in hook_entity_info? I was hoping for something like the following.

'entity keys' => array(
  'id' => 'id',
  'store_ref_id' => 'store_ref_id',
), 

I have a content type store with its ID, and a new entity_type product. I would like to have a field in the new entity referenced to content type.

How can I do this?

Would it be better to re-use the already created field, which is used as reference between content types?

Answer 1

You can attach this field like any other:

function MY_MODULE_install() {
  // Create a field for company reference to be used by various entities
  $field = array(
    'field_name' => 'company_reference',
    'type' => 'entityreference',
    'settings' => array(
      'target_type' => 'company',
      'handler_settings' => array('target_bundles' => NULL),
    ),
    'cardinality' => 1,
    'translatable' => FALSE,
  );
  field_create_field($field);

  // Attach the company reference field to employee instance
  $instance = array(
    'field_name' => 'company_reference',
    'entity_type' => 'employee',
    'bundle' => 'employee',
    'label' => 'Company',
    'required' => false,
    'widget' => array(
      'type' => 'options_select'
    ),
    'settings' => array(
      'target_type' => 'company',
      'handler_settings' => array('target_bundles' => NULL),
    ),
    'display' => array(
      'default' => array('label' => 'inline', 'type' => 'entityreference_label'),
    ),
  );
  field_create_instance($instance);
}

Code sample taken from this more comprehensive manual.