Multiple layers of has_many :through

rubyonrails-talk
1

Either this is not supported or I'm just not seeing the forest for the trees. Here's the model relationship I currently have that works:

class Officer < AR::Base   has_many :clients, :through => :officer_relationships end

class Clients < AR::Base   has_many :officers, :through => :officer_relationships   has_many :accounts end

class OfficerRelationships < AR::Base   belongs_to :client   belongs_to :officer end

My problem is that I'm trying to associate the Account's model through the OfficerRelationship model and the Client model by doing the following:

class Officer < AR::Base   has_many :clients, :through => :officer_relationships   has_many :accounts, :through => :clients end

or the following:

class Officer < AR::Base   has_many :clients, :through => :officer_relationships   has_many :accounts, :through => :clients end

class OfficerRelationships < AR::Base   belongs_to :client   belongs_to :officer   has_many :accounts, :through => :client end

None of these work. Am I just trying to get more out of HasManyThrough than it was designed to? If so, can someone point me in the right direction as to the best DRY way to do this without replicating the OfficerRelationship model for every one of the client's accounts?

For what you propose, I don't think the tables could possibly be configured properly. (Repeating things you already know) has_many :through for class A, and class B, with relationship AB expects three tables like so:

table "as" table "bs" table "as_bs"   a_id   b_id

Which you seem to have for your starting configuration. Now, if you add has_many :accounts :through => :clients to the Officer then that means that rails expects the a clients table with:

table "clients"   officer_id   account_id   << whatever other columns are already here >>

and clearly that's not what you want in that table.

I see three options for you:

1. Leave everything as it was when you started. You can select an officer's accounts by

  (officer.clients.collect { |c| c.accounts }).flatten

If the number of records aren't too large and you :include the accounts in the officers clients has_many like so

  has_many :clients, :through => officer_relationships, :include => :accounts

the performance should be fine

2. If an account belongs to one and only one officer, add those associations and table column

Officer   has_many :accounts

Account   belongs_to :officer

accounts   officer_id

and you could use before_create, before_update or other callbacks to ensure that the proper officer for the client is associated with the account.

3. If an account can belong to more than one officer, you could do some sort of crazy three-way has_many :through association with a new OfficerAccounts relationship table. I'm having a hard time visualizing this one in my head, but I suppose if you were careful you could do it.... :slight_smile:

Best,

-r