Choosing the right Model Associations in Rails 4 - ruby-on-rails

Question

I am having trouble deciding which type of association fits best for my application. I have the following models: Firm, Client, and Case.
A Firm handles many Cases. And each Case can have one or more Clients assigned to it. Therefore my initial approach was:
class Firm < ActiveRecord::Base
has_many :cases
has_many :clients
end
class Case < ActiveRecord::Base
belongs_to :firm
has_many :clients
end
class Client < ActiveRecord::Base
belongs_to :firm
has_many :cases
end
But I think something is not right with this. I was thinking a has_many :through Association would be better but I am not sure.

Answer 1

Rails Guides says that “You should use has_many :through if you need validations, callbacks, or extra attributes on the join model”. As the great coding philosopher Avi Flombaum once eluded, how can you possibly know that your join model will not serve an additional purpose this early in the application process. No matter where you are in the development stage, you can never see so far in the future to know you will not need to extend the join table.
Why You Don’t Need Has_and_belongs_to_many Relationships
With that out of the way:
# models/firm.rb
class Firm < ActiveRecord::Base
has_many :clients
has_many :cases, through: :clients
end
# models/client.rb
class Client < ActiveRecord::Base
belongs_to :firm
has_many :client_cases
has_many :cases, through: :client_cases
end
# models/case.rb
class Case < ActiveRecord::Base
has_many :client_cases
has_many :clients, through: :client_cases
end
# models/client_case.rb
class ClientCase < ActiveRecord::Base
belongs_to :client
belongs_to :case
end
UPDATE
Your issue must lie somewhere else; I was able to create the following in a terminal without any errors.
f = Firm.create name: 'Magical Group' # => #<Firm id: 1...
b = f.clients.create name: 'Billy' # => #<Client id: 1...
m = f.clients.create name: 'Megan' # => #<Client id: 2...
c = Case.create name: 'Billy & Megan are getting married!' # => #<Case id: 1...
b.cases << c # => #<ActiveRecord::Associations::CollectionProxy
m.cases << c # => #<ActiveRecord::Associations::CollectionProxy
f.cases.count # => 2
f.cases.uniq.count # => 1
I've provide the database schema, make sure yours resembles:
ActiveRecord::Schema.define(version: 20150813173900) do
create_table "cases", force: :cascade do |t|
t.string "name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "client_cases", force: :cascade do |t|
t.integer "client_id"
t.integer "case_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "client_cases", ["case_id"], name: "index_client_cases_on_case_id"
add_index "client_cases", ["client_id"], name: "index_client_cases_on_client_id"
create_table "clients", force: :cascade do |t|
t.string "name"
t.integer "firm_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "clients", ["firm_id"], name: "index_clients_on_firm_id"
create_table "firms", force: :cascade do |t|
t.string "name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
end

Answer 2

Assuming that a case will never belong to a different firm:
class Firm < ActiveRecord::Base
has_many :clients
has_many :cases, through: :clients
end
class Client < ActiveRecord::Base
belongs_to :firm
has_and_belongs_to_many :cases
end
class Case < ActiveRecord::Base
has_and_belongs_to_many :clients
end
Migrate join table
rails g migration CreateJoinTableCaseClient case client