Rails: order using a has_many/belongs_to relationship

Question

I was wondering if it was possible to use the find method to order the results based on a class\'s has_many relationship with another class. e.g.

# has the colum         


        

Answer 1

You need to join the related table to the request.

@result = DogTag.find(:all, :joins => :dog, :order => 'dogs.name')

Note that dogs is plural in the :order statement.

Answer 2

In Rails 4 it should be done this way:

@result = DogTag.joins(:dog).order('dogs.name')

or with scope:

class DogTags < ActiveRecord::Base
  belongs_to :dog
  scope :ordered_by_dog_name, -> { joins(:dog).order('dogs.name') }
end

@result = DogTags.ordered_by_dog_name

The second is easier to mock in tests as controller doesn't have to know about model details.