Multiple layers of has_many :through

Rails
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?

2

On Dec 13, 2:24 am, Marc L. [email protected] wrote:

end
class Officer < AR::Base

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

  1. 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.

  1. 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

3

If Officer has_many Clients and Clients has_many Accounts then the
query:

Officer.find(id, include {:clients => :accounts}

should return all the data you need.

4

That should be:

Officer.find(id, include => {:clients => :accounts}

5

Thanks everyone. Not quite what I was hoping for, but at least I know
I’m doing all I can.

6

On Dec 13, 2006, at 2:24 AM, Marc L. wrote:

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 :officer_relationships

has_many :clients, :through => :officer_relationships
end

class Clients < AR::Base

has_many :officer_relationships

the OfficerRelationship model and the Client model by doing the
following:

class Officer < AR::Base

has_many :officer_relationships

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

or the following:

class Officer < AR::Base

has_many :officer_relationships

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?

The has_many :xs :through => :ys also needs to have the has_many :ys

You want:
officer = Officer.find(1)

officer.clients #=> to be all the clients
officer.accounts #=> to be all the accounts

If the double-layer of has_many :through isn’t working for you, you
could always get officer.accounts by adding:

class Officer < ActiveRecord::Base
def accounts
self.clients.map(&:accounts).flatten
end
end

You end up with a normal Array rather than an association proxy of
the accounts, but perhaps this is enough for you needs, yes?

-Rob

Rob B. http://agileconsultingllc.com
[email protected]