(As with Listing 11.4, the test for dependent :destroy is left as an exercise [Section 11.5].) Note that we actually have to include the class name for this association, i.e.,

because otherwise Rails would look for a ReverseRelationship class, which doesn’t exist. It’s also worth noting that we could actually omit the :source key in this case, using simply

since, in the case of a :followers attribute, Rails will singularize ‘‘followers’’ and automatically look for the foreign key follower_id in this case. I’ve kept the :source key to emphasizethe parallel structure with the has_many :followed_users association, but you are free to leave it off.

       With the code in Listing 11.16, the following/follower associations are complete, and all the tests should pass:  

This section has placed rather heavy demands on your data modeling skills, and it’s fine if it takes a while to soak in. In fact, one of the best ways to understand the associations is to use them in the web interface, as seen in the next section.