Symfony2如何在多对多连接表中继承外键

Question

I have a simple structure of three tables and a join table Tournament has a OneToMany with Group. Group also has a ManyToMany with Team.

this is all well and simple, but as you can see in the above image there is group_tournament_id key "inherited"(if that's the right term) from the Tournament table, this to me is very helpful as i can list all teams in the tournament, without looping through all the Group table.

so, how do i get this field to appear in the jointable using symfony 2 and doctrine

thanks

Answer 1

This is a very common thing. It can not be done with ManyToMany relation. Instead, you need to have an "join entity", GroupTeamOwnership.

That entity should have one group, one team id, and one tournament id.

So instead having ManyToMany, you will have:

Group <-OneToMany-> GroupTeamOwnership <-ManyToOne-> Team

In fact, this is so common scenario that doctrine docs even mention it:

Why are many-to-many associations less common? Because frequently you want to associate additional attributes with an association, in which case you introduce an association class. Consequently, the direct many-to-many association disappears and is replaced by one-to-many/many-to-one associations between the 3 participating classes.