Let's assume I have two Entities in my Symfony2 bundle, User and Group. Associated by a many-to-many relationship.
    ┌────────────────┐         ┌────────────────┐         ┌────────────────┐
    |      USER      |         | USER_GROUP_REL |         |     GROUP      |
    ├────────────────┤         ├────────────────┤         ├────────────────┤
    | id#            ├---------┤ user_id#       |    ┌----┤ id#            |
    | username       |         | group_id#      ├----┘    | groupname      |
    | email          |         | created_date   |         |                |
    └────────────────┘         └────────────────┘         └────────────────┘
What would be a good practice or a good approach to add additional columns to the join table, like a created date which represents the date when User joined Group?
I know that I could use the QueryBuilder to write an INSERT statement.
But as far as I have not seen any INSERT example of QueryBuilder or native SQL which makes me believe that ORM/Doctrine try to avoid direct INSERT statements (e.g. for security reasons). Plus as far as I have understood Symfony and Doctrine I would be taken aback if such a common requirement wouldn't be covered by the framework.