Adding a join in a Views field handler class constructor?

Question

In a Views field handler, one can define additional fields to accompany the base field defined in hook_field_data. These field values are based on database columns on the same row, and they can be used in the render function. Somewhat like this:

my_views_field_handler extends views_handler_field {

  function construct() {
    parent::construct();
    $this->additional_fields['property2'] = 'property2';
  }

  function render($values) {
    return $this->get_value($values) . $this->get_value($values, 'property2');
  }

}

But is it also possible to define a join in the constructor? One of my database columns is an id of another entity. I have been using it somewhat like this, but this generates quite a lot of overhead (loading an entire entity for each row).

  function render($values) {
    $id = $this->get_value($values, 'property2');
    $entity = entity_load_single('my_type', $id);

    if ($entity->some_other_field == TRUE) {
      return $this->get_value($values);
    }
    else {
      return 'none';
    }
  }

So is there something like a join I can use in the constuctor, so I can query the other entity table directly instead of having to load the entity?

Answer 1

Yes, but you need to have already defined that relationship in the view. Per the docs for views_handler_field::add_additional_fields($fields):

@param $fields
An array of fields. The key is an identifier used to later find the field alias used. The value is either a string in which case it's assumed to be a field on this handler's table; or it's an array in the form of
@code array('table' => $tablename, 'field' => $fieldname) @endcode

Thus, say you had a field handler for a field on the node table with a defined author relationship to the users table. You could do this:

  function construct() {
    parent::construct();
    $this->additional_fields['mail'] = array(
      'table' => 'users',
      'field' => 'mail',
    );
  }

Which would allow you to do this:

function render($values) {
  //Get the mail column from the users table.
  $this->get_value($values, 'mail');
}

For your case, you'll need to define the entity relationship to your base table before you can do this.