has_many: through, :class_name, :foreign_key

rubyonrails-talk
1

Hello!

When we use has_many :through, is there a way to specify the name of the class and the foreign key? This question pops up when the join table has fields that are not named according to names of the joinable tables.

Thanks.

2

Ivan Ukhov wrote:

Hello!

When we use has_many :through, is there a way to specify the name of the class and the foreign key? This question pops up when the join table has fields that are not named according to names of the joinable tables.

Thanks.

Hey,

Say you have two entities A and B which need to have m->n relationship in the ERM, so ideally they would have a join table A_B_join_table with the foreign keys from both A and B.

Now, say sometime later you decide that the join table should also contain some additional data that would help your business logic. That's the time when you should make the join table an active record model,say C. But it should not break the relationship between A and B too.

That's when you can use A has_many B through C where C is also an active record model. Result A -> C -> B similar to A -> B as earlier.

Also, in Rails 2.0, that uses RESTful architecture, it is emphasized to use active record models instead of stand-alone join tables.

Check out the RailsConf Keynote by DHH. Make sure you have downloaded the pdf before watching the video.