/**
  * Add gridField class to list of field of grid view in editor.
  * 
  * @param gridField $field definition of field.
  * @return Abstract_table_collection reference to this object.
  */
 protected function addGridField(gridField $field)
 {
     $field_index = $field->getField();
     if (!isset($this->grid_settings['fields'][$field_index])) {
         $this->grid_settings['fields'][$field_index] = $field;
     }
     return $this;
 }
 /**
  * Adds gridField to the list of foreign table row fields.
  * 
  * @param gridField $field grid field object.
  * @return editorFieldMMRelation reference to this object.
  */
 public function addGridField(gridField $field)
 {
     $fname = $field->getField();
     if (in_array($fname, $this->grid_fields)) {
         return $this;
     }
     $this->grid_fields[] = $field;
     return $this;
 }