Routing Error for a model with a join_table and has_many :through in RailsAdmin

Question

So I have 3 models: `category`, `product`, `category_products`. This is my `category.rb` ``` attr_accessible :name has_many :category_products do def with_products includes(:product) end end has_many :products, :through => :category_products ``` This is my `product.rb` ``` attr_accessible :name, :description, :price, :vendor_id, :image, :category_ids belongs_to :vendor has_many :category_products do def with_categories includes(:category) end end has_many :categories, :through => :category_products ``` This is my `category_product.rb` ``` attr_accessible :product_id, :category_id, :purchases_count belongs_to :product belongs_to :category validates_uniqueness_of :product_id, :scope => :category_id ``` This is my `routes.rb` ``` mount RailsAdmin::Engine => '/admin', :as => 'rails_admin' resources :categories resources :vendors do resources :products end authenticated :user do root :to => 'home#index' end root :to => "home#index" devise_for :users resources :users ``` When I click on `Ca…

Accepted Answer

Check all the CategoryProduct objects have foreign keys: category_id and product_id.

```
CategoryProduct.all.each {|c| raise("Repair #{c.id}") unless c.category && c.product}
```

Dec 21 update:

How i've installed brand new Rails 3.2.9 with Category, Product and CategoryProduct. Model's relationship code is identical, RailsAdmin with default settings.

And it works with no any problems!

I decided to test my hypothesis. I think maybe when you went from the HABTM to the HM2HM you have missed (forgot) to reestablish key column ID for CategoryProduct which is now not just a join-model, but an independent entity.

So, routing error like:

```
No route matches {:action=>"show", :model_name=>"category_product", :id=>nil, :controller=>"rails_admin/main"}
```

can be result of missing id.

Well I disabled CategoryProduct's id field manually (def id; nil; end).

and yes it is:

```
No route matches {:action=>"show", :model_name=>"category_product", :id=>nil, :controller=>"rails_admin/main"}
```

Routing Error for a model with a join_table and has_many :through in RailsAdmin

Solution

Problem