allow customisation of shortcodable DataObject list in dropdown. Fixes …

…#3

README.md

@@ -67,7 +67,17 @@ public static function parse_shortcode($arguments, $content, $parser, $shortcode
 		return $gallery->customise($data)->renderWith('ImageGallery');
 	}
 }
-```
+``` 
 
 Create the ImageGallery.ss template then that's it, done!
 
+
+### Optional configuration
+
+If you would like to customise or filter the list of available shortcodable DataObject records available in the dropdown, you can supply a custom get_shortcodable_records static method on your shortcodable DataObject. The method should return an associative array suitable for the DropdownField. For example:
+
+```php
+public static function get_shortcodable_records(){
+	return ImageGallery::get()->filter('SomeField', 'SomeValue')->map()->toArray();
+}
+```

code/controllers/ShortcodableController.php

@@ -64,7 +64,11 @@ public function ShortcodeForm(){
 			if (class_exists($classname)) {
 				$class = singleton($classname);
 				if (is_subclass_of($class, 'DataObject')) {
-					$dataObjectSource = $classname::get()->map()->toArray();
+					if(singleton($classname)->hasMethod('get_shortcodable_records')){
+						$dataObjectSource = $classname::get_shortcodable_records();
+					}else{
+						$dataObjectSource = $classname::get()->map()->toArray();	
+					}
 					$fields->push(
 						DropdownField::create('id', $class->singular_name(), $dataObjectSource)
 							->setHasEmptyDefault(true)