Multiple associations with one table

I've searched a bit before asking this but I definitely can't get it working...

I've got a Group model which has a manager_id, a designer_id and other user ids corresponding to different user roles in this group. They are has_one User associations in the Group model with different foreign keys.

I've tried mul开发者_开发知识库tiple belongs_to associations in the User model but... a User which belong to the group (they have a group_id column) can be one of these roles and I realy don't know how to check these and how to do the associations in the User model.

Thank you in advance.

PS: The users can just belong to one group, that's why I've simply put the group_id in the User model and not on a join table.

If being a manager or a designer in a group means that someone is a member if that group, there's no way you can do this easily, you should create a membership model, that has a "role" property that says which role the user represents in a specific group, here's how it would look like:

class User
  has_one :membership
end

class Group
  has_many :memberships
end

class Membership
  belongs_to :group
  belongs_to :user
  validates_presence_of :role
  validates_inclusion_of :role, :in => [ 'manager', 'designer', 'member' ]
  validates_uniqueness_of :user_id, :scope => :group_id
end

This gives you the functionality and even allow you to define as many roles for your groups as possible.

belongs_to is more powerful than you might imagine

For example, to create a belongs_to association about Managers, on the User

In your User class:

belongs_to :manager, :primary_key => :manager_id, :class_name => "User"

Which will do the query, querying where the manager_idfield in the User(s) table matches the manager_id in the Group(s) table.

Or, if the column in the user table is not called "manager_id":

belongs_to :manager, :foreign_key => :my_manager_id, :primary_key => :manager_id

Which will match the my_manager_id column in the User(s) table to the manager_id column in the Group(s) table.

Then you should be able to do:

user.manager.exists?

and what-have-you

Edit: It's also possible I'm not quite understanding your data model, but I think this approach may also work with a has_one :manager, :through => :group situation. has_one :manager, :through => :group, for example. Except :foreign_key and class_name doesn't work in these situations, per the documentation for has_on, because "Options for :class_name and :foreign_key are ignored, as the association uses the source reflection".