Followed users

We come now to the heart of the Relationship associations: followed_users and followers. We start with followed_users, as shown Listing 11.9.

The implementation uses has_many through for the first time: A user has many following through relationships, as illustrated in Figure 11.7. By default, in a has_many through association Rails looks for a foreign key corresponding to the singular version of the association; in other words, code like

would assemble an array using the followed_id in the relationships table. But, as noted in Section 11.1.1, user.followeds is rather awkward; far more natural is to use ‘‘followed users’’ as a plural of ‘‘followed,’’ and write instead user.followed_users for the array of followed users. Naturally, Rails allows us to override the default, in this case using the :source parameter (Listing 11.10), which explicitly tells Rails that the source of the followed_users array is the set of followed ids.