Using a Many-to-Many Relationship

Okay, so I have a many-to-many relationship between users and groups
set up in my application, using a join table (users_groups). I am able
to reference one from the other using this relaionship. However, I’m
not exactly sure how to relate a User to a Group in the app, other
than hard-coding some SQL to insert a new relationship. What’s the
proper way to do this?

You should be able to append instances of one to the collection accessor
of the other. So for instance:

fred = User.find_by_name(“fred”)
godlike_beings = Group.find_by_name(“godlike beings”)

godlike_beings.users << fred

or equivalently:

fred.groups << godlike_beings



The one caveat to Roy’s response is that both the User and the Group
must exist. It’s tempting to use that same line of coding when you’re
creating the end points and the join table at the same time but it
doesn’t work.

True dat. I’ve found that to be a bit challenging myself (as evidenced
by my questions over the last few weeks). FWIW, I took the fields_for +
virtual attribute approach Ryan B. explains in these railscasts:

Took me a while to get my head around that, but it seems to work…

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