Question

What do you think is the most optimal way to retrieve all attributes for all the associations an AR model has?

i.e: let’s say we have the model Target.

class Target < ActiveRecord::Base
  has_many :countries
  has_many :cities
  has_many :towns
  has_many :colleges
  has_many :tags

  accepts_nested_attributes_for :countries, :cities, ...
end

I’d like to retrieve all the association’s attributes by calling a method on a Target instance:

target.associations_attributes
>> { :countries => { "1" => { :name => "United States", :code => "US", :id => 1 }, 
                     "2" => { :name => "Canada", :code => "CA", :id => 2 } },
     :cities => { "1" => { :name => "New York", :region_id => 1, :id => 1 } },
     :regions => { ... },
     :colleges => { ... }, ....
   }

Currently I make this work by iterating on each association, and then on each model of the association, But it’s kind of expensive, How do you think I can optimize this?

Just a note: I realized you can’t call target.countries_attributes on has_many associations with nested_attributes, one_to_one associations allow to call target.country_attributes

Answer 1

I’m not clear on what you mean with iterating on all associations. Are you already using reflections?

Still curious if there’s a neater way, but this is what I could come up with, which more or less results in the hash you’re showing in your example:

class Target < ActiveRecord::Base
  has_many :tags

  def associations_attributes
    # Get a list of symbols of the association names in this class
    association_names = self.class.reflect_on_all_associations.collect { |r| r.name }
    # Fetch myself again, but include all associations
    me = self.class.find self.id, :include => association_names
    # Collect an array of pairs, which we can use to build the hash we want
    pairs = association_names.collect do |association_name|
      # Get the association object(s)
      object_or_array = me.send(association_name)
      # Build the single pair for this association
      if object_or_array.is_a? Array
        # If this is a has_many or the like, use the same array-of-pairs trick
        # to build a hash of "id => attributes"
        association_pairs = object_or_array.collect { |o| [o.id, o.attributes] }
        [association_name, Hash[*association_pairs.flatten(1)]]
      else
        # has_one, belongs_to, etc.
        [association_name, object_or_array.attributes]
      end
    end
    # Build the final hash
    Hash[*pairs.flatten(1)]
  end
end

And here’s an irb session through script/console to show how it works. First, some environment:

>> t = Target.create! :name => 'foobar'
=> #<Target id: 1, name: "foobar">
>> t.tags.create! :name => 'blueish'
=> #<Tag id: 1, name: "blueish", target_id: 1>
>> t.tags.create! :name => 'friendly'
=> #<Tag id: 2, name: "friendly", target_id: 1>
>> t.tags
=> [#<Tag id: 1, name: "blueish", target_id: 1>, #<Tag id: 2, name: "friendly", target_id: 1>]

And here’s the output from the new method:

>> t.associations_attributes
=> {:tags=>{1=>{"id"=>1, "name"=>"blueish", "target_id"=>1}, 2=>{"id"=>2, "name"=>"friendly", "target_id"=>1}}}