Using many-to-many nested models in Rails

Question

I've got the following situation setup to model a Customer with multiple addresses and a reference table for the type of address. The data model is Customer - Address : many to many relationship, represented with a join table called 'Location'.
LocationType - Location : one to many, so that a locationtype (eg 'work', 'home') can have many associations to a Location.

What i'm trying to achieve is the ability to simply locate all the 'work' addresses for a customer, or the 'delivery' addresses. Whilst avoiding having the text duplicated in the join table Location

The model(s) look like:

class Address < ActiveRecord::Base
  has_many :locations  
  has_many :customers, :through => :locations  
end

class Customer < ActiveRecord::Base  
   has_many :locations  
   has_many :addresses, :through => :locations do  
   def special_location(loc)  
    find :all, :conditions => ['addr_type == ?', loc]  
   end  
  end  
end 

class Location < ActiveRecord::Base
    belongs_to :address
    belongs_to :customer
    belongs_to :locationtype
end

class LocationType < ActiveRecord::Base
    has_many :locations
end

This works ok for the simple cases of :

@customer = Customer.find(1)  
@customer.addresses   # return all addresses

And with the 'special helper method' of special_location("string") I can achieve the result. What I wanted to find out is how I could achieve the same via the use of the additional reference table (LocationType)
Something along the lines of

@customer.addresses.find_locationtype("work")

Answer 1

You can add some tables to be joined in the select request.

def find_locationtype(type)
    find :all, :conditions => ['location_types.name = ?', type], :joins => :location, :locationtype
end

When you do customer.find_locationtype('work'), the generated query will join the tables location and locationtype. So you'll have access to every field from these two tables and be able to add conditions on them.