doc about adding possibility to filter with choice

reference/en/09 - Admin generator.markdown

@@ -186,3 +186,35 @@ $(function(){
 	});
 });
 [/code]
+
+##Custom filters
+
+### Filtering with a choice widget
+Many time we define types of some field:
+[code php]
+class PersonTable extends myDoctrineTable
+{
+  static public $genders = array(
+    1 => 'Male',
+    2 => 'Female',
+  );
+}
+[/code]
+
+In the form filter, the autogenerated widget is and input, but we would like to use a choice, so we change the widget:
+
+[code php]
+    public function configure()
+  {
+    //add empty choice
+    $gender_choices = array(null => null) + PersonTable::$genders;
+
+    $this->widgetSchema['gender'] = new sfWidgetFormChoice(array(
+          'choices' => $gender_choices
+    ));
+    $this->validatorSchema['gender'] = new sfValidatorChoice(array(
+          'required' => false,
+          'choices' => array_keys($gender_choices)
+    ));
+  }
+[/code]