Question

I have three classes; User, Feed, and Entries. Users have one or more Feeds and Feeds have one or more Entries:

class Feed < ActiveRecord::Base
  has_many :entries
  has_many :feeds_users
  has_many :users, :through => :feeds_users, :class_name => "User"
end

Class User < ActiveRecord::Base
  has_many :feeds_users
  has_many :feeds, :through => :feeds_users, :class_name => "Feed"
end

class Entry < ActiveRecord:Base
  belongs_to :feed
end

The User and Feed classes are related through a third table:

class FeedsUser < ActiveRecord::Base
  belongs_to :user
  belongs_to :feed
end

Now, my problem is that I need to get a certain user’s feeds and each feed’s latest n entries. I’m fiddling with something like this:

u = User.first
Feed.joins(:entries, :users).where(:entries => { :created_at => (Time.now-2.days)..Time.now }, :users => u)

My problem here is that this generates some SQL that tries to query “users” on the table “feeds” – which doesn’t exist.

How do I go about creating a correct query that can give me all feeds and their latest 10 entries for a given user?

Answer 1

Take out has_many :feeds_users. :feeds_users shouldn’t be a model.

You should keep the table, but some Rails magic goes on behind the scenes. If you have a table named feeds and a table named users, Rails derives the table name of the look-up unless you specify it differently.

For your example:

Class Feed < ActiveRecord::Base
  has_many :users
end

Class User < ActiveRecord::Base
  has_many :feeds
end

It will look for the relationship in the users_feeds table. If it looked like this:

Class Feed < ActiveRecord::Base
  belongs_to :user
end

Class User < ActiveRecord::Base
  has_many :feeds
end

It would look for the relationship in the user_feeds table.

It’s linguistically correct, as many users will have many feeds in the first example, and one user will have many feeds in the second example. That’s also a good indicator of whether your relation logic is correct.

It also sounds like you need the has_and_belongs_to_many relationship instead of just has_many.

For a complete run-down on all forms of model associations, check out the guide.