Fix association

README.md

@@ -77,13 +77,18 @@ Output:
 ### Associations
 You may include associated objects. Say for example, a user has projects:
 ```ruby
+class ProjectBlueprint < Blueprinter::Base
+  identifier :uuid
+  field :name
+end
+
 class UserBlueprint < Blueprinter::Base
   identifier :uuid
   field :email, name: :login
 
   view :normal do
     fields :first_name, :last_name
-    association :projects
+    association :projects, blueprint: ProjectBlueprint
   end
 end
 ```

lib/blueprinter/base.rb

@@ -87,6 +87,8 @@ def self.field(method, options = {}, &block)
     #
     # @param method [Symbol] the association name
     # @param options [Hash] options to overide defaults.
+    # @option options [Symbol] :blueprint Required. Use this to specify the
+    #   blueprint to use for the associated object.
     # @option options [Symbol] :name Use this to rename the association in the
     #   JSON output.
     # @option options [Symbol] :view Specify the view to use or fall back to
@@ -95,12 +97,13 @@ def self.field(method, options = {}, &block)
     # @example Specifying an association
     #   class UserBlueprint < Blueprinter::Base
     #     # code
-    #     association :vehicles, view: :extended
+    #     association :vehicles, view: :extended, blueprint: VehiclesBlueprint
     #     # code
     #   end
     #
     # @return [Field] A Field object
     def self.association(method, options = {})
+      raise BlueprinterError, 'blueprint required' unless options[:blueprint]
       name = options.delete(:name) || method
       current_view << Field.new(method,
                                        name,

lib/blueprinter/serializers/association_serializer.rb

@@ -1,10 +1,8 @@
 class Blueprinter::AssociationSerializer < Blueprinter::Serializer
   def serialize(association_name, object, local_options, options={})
-    if options[:blueprint]
-      view = options[:view] || :default
-      options[:blueprint].prepare(object.public_send(association_name), view_name: view, local_options: local_options)
-    else
-      object.public_send(association_name)
-    end
+    value = object.public_send(association_name)
+    return value if value.nil?
+    view = options[:view] || :default
+    options[:blueprint].prepare(value, view_name: view, local_options: local_options)
   end
 end

spec/integrations/base_spec.rb

@@ -67,6 +67,40 @@
       let(:vehicle) { create(:vehicle) }
 
       include_examples 'Base::render'
+
+      context 'Given blueprint has ::association' do
+        let(:result) do
+          '{"id":' + obj_id + ',"vehicles":[{"make":"Super Car"}]}'
+        end
+        let(:blueprint_without_associated_blueprint) do
+          Class.new(Blueprinter::Base) do
+            identifier :id
+            association :vehicles
+          end
+        end
+        before { vehicle.update(user: obj) }
+        context 'Given associated blueprint is given' do
+          let(:blueprint) do
+            vehicle_blueprint = Class.new(Blueprinter::Base) do
+              fields :make
+            end
+            Class.new(Blueprinter::Base) do
+              identifier :id
+              association :vehicles, blueprint: vehicle_blueprint
+            end
+          end
+          it('returns json with association') { should eq(result) }
+        end
+        context 'Given no associated blueprint is given' do
+          let(:blueprint) do
+            Class.new(Blueprinter::Base) do
+              identifier :id
+              association :vehicles
+            end
+          end
+          it { expect{subject}.to raise_error(Blueprinter::BlueprinterError) }
+        end
+      end
     end
   end
 end