How to specify a 3-way relation in Active Record?

rubyonrails-talk
1

I have 3 database tables, Users, Projects and Roles.There is a 3-way relation between them which indicates with what role a user is allocated to a specific project.

I have a join table with 3 columns as the foreign key’s to 3 tables mentioned above.

The only solution that comes to my mind is following,

  1. Have a model for the join table having

belongs_to :user,:role,:user

Is there a solution where I can do away with the model for the join table(the way habtm does)?

Regards,

Jatinder

2

A user has_many projects, a Project has_many Users, but each role is associated with 1 user + 1 Project ... i suggest to use has_many :through and use a join table "project_meberships"

class User   has_many :project_memberships   has_many :projects, :through => :project_memberships end class Project   has_many :project_memberships   has_many :users, :through => :project_memberships end class ProjectMembership   belongs_to :user   belongs_to :project   belongs_to :role end class Role   has_many :project_memberships end

the table "project_memberships" should look something like this: id #primary key, auto increment user_id project_id role_id (additional fields like description)

This assumes you have pre-defined Roles like Admin, Teamleader, Participant etc. pp. in the roles table.

@user = User.find(1) role = @user.project_memberships(1).role project = @user.project_memberships(1).project

You might want to read this about eager loading those associations with a nested :include in the find command.