public function set_display_name($model_classname, $field_expression)
	{
	    $model_instance = $this->get_model_instance($model_classname);
	    
	    $schema = $model_instance->schema();
	    
	    if(array_key_exists($field_expression, $schema)
	        ||
	       array_key_exists(str_replace($model_classname . '.', '', $field_expression), $schema)
	        ||
	       array_key_exists($field_expression, $model_instance->virtualFields))
	    {
	        /*
	         * The field does not need to be created as it already exists in the model
	         * as a datatable field, or a virtual field configured in the model
	         */
	        
	        /*
	         * Eventually remove the model name
	         */
	        if(strpos($field_expression, $model_classname . '.') === 0)
	        {
	            $field_expression = str_replace($model_classname . '.', '', $field_expression);
	        }
	        
	        return $field_expression;
	    }
	    else
	    {
	        /*
	         * The field does not exist in the model
	         * -> create a virtual field with the given expression
	         */
	        
	        $this->controller->{$model_classname}->virtualFields['alaxos_acl_display_name'] = $field_expression;
	        
	        return 'alaxos_acl_display_name';
	    }
	}