Rails: Bad Associations? [has_many , through] How to test if working? - ruby-on-rails

Question

I am struggling with an issue in my data model. I do have the following models:
class User < ActiveRecord::Base
...
has_many :claims #user-claims
has_many :claims, through: :rulings, as: :commissars
...
end
class Claim < ActiveRecord::Base
...
belongs_to :user
has_many :users, through: :rulings, as: :commissars
...
end
class Ruling < ActiveRecord::Base
belongs_to :user
belongs_to :claim
end
Error:
undefined method `commissars' for #<Claim:0xc5ac090>
Model Explanation:
User can write claims (A claim belongs to one user), and users could do the role of commissars to do the ruling of the claim (max numbers of commissars = 3 per claim).
Is there any way to fix this or improve the relationship?

Answer 1

This domain model requires som pretty complex relations so there is no shame in not getting it on the first try.
Lets start with user and claims:
class User < ActiveRecord::Base
has_many :claims, foreign_key: 'claimant_id',
inverse_of: :claimant
end
class Claim < ActiveRecord::Base
belongs_to :claimant, class_name: 'User',
inverse_of: :claims
end
This is a pretty basic one to many relation with a twist. Since User will have a bunch of relations to Claim we call the relation something other than the default user so that the nature of the relation is defined.
The class_name: 'User' option tells ActiveRecord to load the class User and use it to figure out what table to query and also what class to return the results as. Its needed whenever the class name cannot be directly derived from the name of the association. The option should be a string and not a constant due to the way Rails lazily resolves class dependencies.
Now lets add the commissar role. We will use ruling as the join table:
class Ruling < ActiveRecord::Base
belongs_to :claim
belongs_to :commissioner, class_name: 'User'
end
Notice that here we have a relation to User that we call commissioner for clarity. Now we add the relations to Claim:
class Claim < ActiveRecord::Base
belongs_to :claimant, class_name: 'User',
inverse_of: :claims
has_many :rulings
has_many :commissioners, through: :rulings
end
Then we need to setup the relations on the User side:
class User < ActiveRecord::Base
has_many :claims, foreign_key: 'claimant_id',
inverse_of: :claimant
# rulings as claimant
has_many :rulings, through: :claims
has_many :rulings_as_commissioner, class_name: 'Ruling',
foreign_key: 'commissioner_id'
has_many :claims_as_commissioner, through: :rulings_as_commissioner,
source: :claim
end
Note the source: :claim option where we tell ActiveRecord which party we want from the join table.
Of course for this to work we need to setup the columns and the foreign keys properly. These migrations are to create the tables from scratch but you can easily rewrite them to alter your existing tables:
class CreateClaims < ActiveRecord::Migration
def change
create_table :claims do |t|
t.belongs_to :claimant, index: true, foreign_key: false
t.timestamps null: false
end
# we need to setup the fkey ourself since it is not conventional
add_foreign_key :claims, :users, column: :claimant_id
end
end
class CreateRulings < ActiveRecord::Migration
def change
create_table :rulings do |t|
t.belongs_to :claim, index: true, foreign_key: true
t.belongs_to :commissioner, index: true, foreign_key: false
t.timestamps null: false
end
add_foreign_key :rulings, :users, column: :commissioner_id
add_index :rulings, [:claim_id, :commissioner_id], unique: true
end
end
max numbers of commissars = 3 per claim
This is not really part of the associations rather you would enforce this rule by adding a validation or an association callback.
class Ruling < ActiveRecord::Base
# ...
validate :only_three_rulings_per_claim
private
def only_three_rulings_per_claim
if claim.rulings.size >= 3
errors.add(:claim, "already has the max number of commissars")
end
end
end
See:
Rails Guides: Active Record Migrations
Rails Guides: the has_many though: relations

Answer 2

First, I would suggest you go back and read the Guide carefully as I believe you have fundamentally misunderstood a number of things. The as: option, for instance, does not indicate role but, rather, the presence of a polymorphic join. Also, you can't declare has_many :claims twice on the same model. Anyway, go give it another read.
But, to your question - a functional although somewhat inelegant approach might look like:
class User < ActiveRecord::Base
...
has_many :claims
has_many :claim_commissars, foreign_key: "commissar_id"
has_many :commissar_claims, through: :claim_commissars, class_name: "Claim"
# ^^^^^^^^^^^^^^^^^^^^^
# this bit may be wrong
...
end
class Claim < ActiveRecord::Base
...
belongs_to :user
has_one :ruling
has_many :claim_commissars
has_many :commissars, through: :claim_commissars
...
end
class ClaimCommissar < ActiveRecord::Base
...
belongs_to :claim
belongs_to :commissar, class_name: "User"
...
end
class Ruling < ActiveRecord::Base
...
belongs_to :claim
belongs_to :commissar, class_name: "User"
...
end
You would need to enforce your 'max 3 commissars` in the code.
This is not tested and you will likely need to fiddle with it to get it to go. But, hopefully, it sets you in a better direction.
Good luck!