Question

This is mainly a theoritical question, but just wanted to make sure that i’m doing it correctly. Consider a Ruby Rails project where there are two models, one being User and the other being Alliance.

A user can only have one alliance.
An alliance can have many users.

That is very much simply a :has_many, :belongs_to relationship.

However, i feel that using an intermediate model is a better way to do it. That would be a :has_many :through :users_alliances, where users_alliances would be an intermediate model.

What do you think is the best way to do that ?

Answer 1

Don’t use habtm, it doesn’t make the join into a fully fledged model, which is what you need. Use has_many :through on the alliance side and has_one :through on the user side.

User
  has_one :alliance_membership
  has_one :alliance, :through => :alliance_membership

AllianceMembership
  belongs_to :user
  belongs_to :alliance

Alliance 
  has_many :alliance_memberships
  has_many :users, :through => :alliance_memberships

Personally i prefer the class name AllianceMembership to UserAlliance but you could use either. UsersAlliances is ugly though imo. (another advantage of has_many/one :through is that you can call the join table/class whatever you want).

This gives you the option to easily change to users having many alliances later on if you want.