Erik A. Hanson's Weblog

I had a little trouble today with join tables that contain attributes.

Creating the join table

Starting with tables foos and bars, I created a join table bars_foos. (Rails expects the join table’s name to be a concatenation of the two table names in alphabetical order).

Reading attributes

I added an attribute baz to bars_foos. I had originally tried to access it with:

myFoo.baz

but that didn’t work. It turns out that I needed to force Rails to do the join before accessing the attribute, which makes sense when you think about it (but it took me a while before my little brain thought about it correctly):

myFoo.bars.baz

Adding attributes

Use the well-documented push_with_attributes method:

myFoo.bars.push_with_attributes(bar, :baz => "fez")

Updating attributes

Apparently you can’t. Luckily, in my app the attribute is immutable. Other people have suggested deleting and re-inserting the row which I imagine shouldn’t be a problem for most applications.