# Namespaces, models, and rails associations

> Last updated: 2010-07-04

I spent several hours banging my head against this. I figured I'd
share the solution that a co-worker eventually showed me.

I was working with 3 models all inside the same module.

```ruby
class Billing::Customer < ActiveRecord::Base
  has_and_belongs_to_many :Orders
end

class Billing::Orders < ActiveRecord::Base
  belongs_to :Department
end

class Billing::Department < ActiveRecord::Base
end
```

In the controller for model for Customers I wanted to allow users to
filter the entire list of customers by various criteria. One of the
filters was for first name, which is an attribute of the customer
model. I could do the search like this:

```ruby
Billing::Customer.find(:all, :conditions => "first_name LIKE ")
```

A second filter was only customers who had ordered something. This
was also easy using the :include parameter to the find method.

```ruby
Billing::Customer.find(:all,
                       :conditions => "Orders.id IS NOT NULL", 
                       :include => [:Orders])
```

But the third filter was trickier. I wanted to list the customers
that had orders associated with any department. 

Without the namespace this is the proper way to do a find with nested includes.

```ruby
Billing::Customer.find(:all,
                       :conditions => "Departments.id",
                       :include => [:Orders, {:Orders => :Department}])
```

Because the Orders model is in the Billing module that returned an
error that "Orders" was an uninitialized constant. It worked at the
rails console if I first ran include Orders but I couldn't make it
work in my controller.

The proper way to do this with namespaced models is to make the
association more explicit by specifying the class names.

```ruby
class Billing::Customer < ActiveRecord::Base
  has_and_belongs_to_many :Orders, :class_name => "Billing::Orders"
end
```

With that change the find worked properly and I was able to do the search.