ActiveRecord associations with two different models - ruby-on-rails

Question

I'm having a tough time wrapping my head around how I should be configuring my tables + associations.
I have a Lawsuit model. A lawsuit has_many parties (defendants, plaintiffs, attorneys, etc.). A party, in turn, can either be a Person or a Company. Ultimately, I want to be able to get:
A person’s lawsuits (#person.lawsuits);
A company’s lawsuits (#company.lawsuits); and
A lawsuit’s parties (#lawsuit.parties), which can be either people or companies.
This is how I have my tables + models set up currently:
people
| id | fname | lname | date_of_birth |
| -- | ------ | ----- | ------------- |
| 1 | John | Smith | 1974-02-04 |
| 2 | George | Glass | 1963-07-29 |
companies
| id | name | duns | ticker | address |
| -- | --------- | --------- | ------ | ------------ |
| 1 | Acme Inc. | 239423243 | ACME | 123 Main St. |
lawsuits
| id | jurisdiction | court | case_no | title |
| -- | ------------ | ----- | ---------- | --------------------------- |
| 1 | federal | SDNY | 18-CV-1234 | Smith v. Glass, Acme, et al |
lawsuit_parties
| id | lawsuit_id | person_id | company_id | role |
| -- | ---------- | --------- | ---------- | --------- |
| 1 | 1 | 1 | | plaintiff |
| 2 | 1 | 2 | | defendant |
| 3 | 1 | | 1 | defendant |
# models/lawsuit.rb:
class Lawsuit < ApplicationRecord
has_many :lawsuit_parties
def parties
self.lawsuit_parties
end
def defendants
self.parties(where(lawsuit_parties: {role: 'defendant'})
end
def plaintiffs
self.parties(where(lawsuit_parties: {role: 'plaintiff'})
end
def attorneys
self.parties(where(lawsuit_parties: {role: 'attorney'})
end
end
# models/lawsuit_party.rb
class LawsuitParty < ApplicationRecord
belongs_to :person
belongs_to :company
end
# models/person.rb
class Person < ApplicationRecord
has_many :lawsuit_parties
has_many :lawsuits, through: :lawsuit_parties
end
# models/company.rb
class Company < ApplicationRecord
has_many :lawsuit_parties
has_many :lawsuits, through: :lawsuit_parties
end
Any help you would be much appreciated…

Answer 1

You're on the right track, but you'll need to introduce a polymorphic relationship onto your Join Model to get this type of modeling to work. An Enum can handle differentiating between Defendants and Plaintiffs, as well as provide several scopes/methods you're asking for for free.
class LawsuitParty < ApplicationRecord
belongs_to :lawsuit
belongs_to :partiable, polymorphic: true
enum role: [:defendant, :plaintiff]
end
You'll need to write a migration to change your lawsuit_parties table to the following columns (all Rails convention names):
partiable_id = Integer
partiable_type = String
role = String
lawsuit_parties
| id | lawsuit_id | partiable_id | partiable_type | role |
| -- | ---------- | ------------ | -------------- | ----------|
| 1 | 1 | 1 | Person | defendant |
| 2 | 1 | 2 | Company | plaintiff |
| 3 | 1 | 1 | Company | defendant |
Next, tell Rails that Person and Company records are associated with many Lawsuit's using has_many's :as option.
class Person < ApplicationRecord
has_many :lawsuit_parties, as: :partiable
has_many :lawsuits, through: :lawsuit_parties
end
Add the same has_many :lawsuit_parties, as: :partiable to Company, or any other models that may come later (i.e. Judge or JuryMember).
Once you have a LawsuitParty setup like this, you should be all set.