Question

A User can have many roles, but only one role per Brand.

Class User < AR::Base
    has_and_belongs_to_many :roles, :join_table => "user_brand_roles"
    has_and_belongs_to_many :brands, :join_table => "user_brand_roles"
end

The problem with this setup is, how do I check the brand and the role at the same time?

Or would I better off with a BrandRole model where different roles can be set up for each Brand, and then be able to assign a user to a BrandRole?

Class User < AR::Base
has_many :user_brand_roles
has_many :brand_roles, :through => :user_brand_roles
end

Class BrandRole < AR::Base
belongs_to :brand
belongs_to :role
end

Class UserBrandRole < AR::Base
belongs_to :brand_role
belongs_to :user
end

This way I could do a find on the brand for the user:

br = current_user.brand_roles.where(:brand_id => @brand.id).includes(:brand_role)
if br.blank? or br.role != ADMIN
  # reject access, redirect
end

This is a new application and I’m trying to learn from past mistakes and stick to the Rails Way. Am I making any bad assumptions or design decisions here?

Answer 1

Assuming Roles,Brands are reference tables. You can have a single association table Responsibilities with columns user_id, role_id, brand_id.
Then you can define

Class User < AR::Base
 has_many : responsibilities
 has_many :roles, :through => responsibilities
 has_many :brands,:through => responsibilities
end
Class Responsibility < AR::Base
 belongs_to :user
 has_one :role
 has_one :brand
end

The you can define

Class User < AR::Base
  def has_access?(brand)
     responsibility = responsibilities.where(:brand => brand)
     responsibility and responsibility.role == ADMIN
  end
end

[Not sure if Responsibility is the term used in your domain, but use a domain term instead of calling it as user_brand_role]