Rails 4.1.x HABTM Undefined Method 'foreign_key'

Question

The following definition was working in Rails 4.0.x and lower: ``` module Gemgento class Product < ActiveRecord::Base has_and_belongs_to_many :stores, -> { distinct }, join_table: 'gemgento_stores_products', class_name: Gemgento::Store end end ``` However, after upgrading to Rails 4.1.x, I started to receive the following error whenever the `Gemgento::Product` class was initialized. ``` NoMethodError: undefined method `foreign_key' for # from /Users/Kevin/.rvm/gems/ruby-1.9.3-p429@sellect/gems/activerecord-4.1.4/lib/active_record/dynamic_matchers.rb:26:in `method_missing' from /Users/Kevin/.rvm/gems/ruby-1.9.3-p429@sellect/gems/activerecord-4.1.4/lib/active_record/associations/builder/has_and_belongs_to_many.rb:113:in `belongs_to_options' from /Users/Kevin/.rvm/gems/ruby-1.9.3-p429@sellect/gems/activerecord-4.1.4/lib/active_record/associations/builder/has_and_belongs_to_many.rb:82:in `through_model' from /Users/Kevin/.rvm/gems/ruby-1.9.3-p429@sellect/gems/activ…

Accepted Answer

After searching for any documented changes to HABTM in Rails 4.1, I couldn't find anything. There were no deprecation warnings in 4.0 either. It turns out that `:class_name` must be defined as a String.

```
module Gemgento
   class Product < ActiveRecord::Base
      has_and_belongs_to_many :stores, -> { distinct }, join_table: 'gemgento_stores_products', class_name: 'Gemgento::Store'
   end
end
```

This change does not affect any other association. But it is probably good to make sure a string is always used from now on.

Rails 4.1.x HABTM Undefined Method 'foreign_key'

Solution

Problem