Resources: SilverStripe
Add field to a many_many relationship
19 November 2014
Sorting dataobjects in a many_many requires the sort to be on the relationship, rather than the parent or child dataobject. You can add any fields to this relationship database with $many_many_extraFields.
MyClass.php
static $many_many_extraFields = array( 'RelationshipFieldName' => array( 'FieldName' => 'FieldType' ) );