Simple has_many :through question

rubyonrails-talk
1

Ok, I have 2 very simple has_many :through associations I need to create and, despite bashing my brain and my computer against this problem repeatedly for 2 days, I cannot figure out what I am doing wrong as I cannot get the has_many :through to work. I think I have fundamentally misunderstood how to do has_many :throughs, so I am going to ruby script/destroy the models I have created and try again. I'm going to post here my steps to create these relationship, can someone please let me know if I'm doing this correctly? First, the relationships.

Contacts <== Account_Contacts ==> Account <== Account_Attachments ==> Attachments

the 2 word tables are the join tables, basically Contacts and Attachments have a many to many relationship with Account.

1. ruby script/generate model Account 2. ruby script/generate model Contact 3. ruby script/generate model Attachment 4. fill in migration file for the account table (no need to reference a join table here) 5. fill in migration file for the contact table (here I am creating the Account_Contacts table with integer fields for Account and Contact, as well as a category field) 6. fill in migration file for the attachment table (Same as the contact table, I create Account_Attachments here with the same fields). 7. rake db:migrate

Ok, now I should have a functioning has_many :through relationship, right? When I attempted to use this relationship in the console like so:

acct = Account.find(1) file = Attachment.find(1) acct.attachments.create( :attachment => file, :category => "test")

I get the following error message:

NameError: uninitialized constant Account::AccountAttachment         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activesupport-1.4.2/lib /active_support/dependencies.rb:477:in `const_missing'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/base.rb:1360:in `compute_type'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/reflection.rb:125:in `send'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/reflection.rb:125:in `klass'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/reflection.rb:177:in `source_reflection'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/reflection.rb:177:in `collect'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/reflection.rb:177:in `source_reflection'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/reflection.rb:186:in `check_validity!'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/associations/has_many_through_association.rb:6:in `initialize'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/associations.rb:934:in `new'         from C:/InstantRails/ruby/lib/ruby/gems/1.8/gems/ activerecord-1.15.3/lib /active_record/associations.rb:934:in `attachments'         from (irb):3

What did I do wrong here?

2

You need to edit the models and add something like

contacts.rb has_many :account_contacts has_many :accounts, :through => :account_contacts

account.rb has_many :account_contacts has_many :contacts, :though => :account_contacts has_many :account_attachments has_many :attachments, :through => :account_attachments

Peace, Phillip

3

Not just longer ;), but actually correct. I forgot the join table models that have the :belongs_to. I don't think it would have worked without that!

Thanks gemblon!

Peace, Phillip