Merged #16.

Author: dblock

CHANGELOG.markdown

@@ -3,6 +3,7 @@ Next Release
 * Ruby 1.8.x is no longer supported - [@dblock](https://github.com/dblock).
 * [#7](https://github.com/intridea/grape-entity/issues/7): Add `serializable` option to `represent` - [@mbleigh](https://github.com/mbleigh).
 * [#18](https://github.com/intridea/grape-entity/pull/18): Add `safe` option to `expose`, will not raise error for a missing attribute - [@fixme](https://github.com/fixme).
+* [#16](https://github.com/intridea/grape-entity/pull/16): Add `:using` option to `expose SYMBOL BLOCK` - [@fahchen](https://github.com/fahchen).
 * Your contribution here.
 
 0.3.0 (2013-03-29)

README.markdown

@@ -41,9 +41,10 @@ array.
   * `expose SYMBOL, { :as => "alias" }`
     * Expose a value, changing its hash key from SYMBOL to alias
     * `:as` can only be applied to one exposure at a time
-  * `expose SYMBOL BLOCK`
+  * `expose SYMBOL, HASH BLOCK`
+    * HASH keys only can be `:using`
     * block arguments are object and options
-    * expose the value returned by the block
+    * expose the value returned by the block (and present by `:using` option)
     * block can only be applied to one exposure at a time
   * `with_options HASH BLOCK`
     * exposures defined within a `with_options` block will inherit any options defined in HASH. Same keys available as `expose SYMBOLS, HASH`
@@ -62,6 +63,9 @@ module API
         Digest::MD5.hexdigest status.txt
       end
       expose :replies, :using => API::Status, :as => :replies
+      expose :last_reply, :using => API::Status do |status, options|
+        status.replies.last
+      end
 
       with_options({ :format_with => :iso_timestamp }) do
         expose :created_at

lib/grape_entity/entity.rb

@@ -374,7 +374,14 @@ def value_for(attribute, options = {})
       exposure_options = exposures[attribute.to_sym]
 
       if exposure_options[:proc]
-        exposure_options[:proc].call(object, options)
+        if exposure_options[:using]
+          using_options = options.dup
+          using_options.delete(:collection)
+          using_options[:root] = nil
+          exposure_options[:using].represent(exposure_options[:proc].call(object, options), using_options)
+        else
+          exposure_options[:proc].call(object, options)
+        end
       elsif exposure_options[:using]
         using_options = options.dup
         using_options.delete(:collection)

spec/grape_entity/entity_spec.rb

@@ -39,8 +39,8 @@
 
         it 'sets the :proc option in the exposure options' do
           block = lambda{|_| true }
-          subject.expose :name, &block
-          subject.exposures[:name][:proc].should == block
+          subject.expose :name, :using => 'Awesome', &block
+          subject.exposures[:name].should == { :proc => block, :using => 'Awesome' }
         end
       end
 
@@ -358,6 +358,27 @@
         end
       end
 
+      it "exposes attributes that don't exist on the object only when they are generated by a block with options" do
+        module EntitySpec
+          class TestEntity < Grape::Entity
+          end
+        end
+
+        fresh_class.expose :nonexistent_attribute, using: EntitySpec::TestEntity do |model, _|
+          "well, I do exist after all"
+        end
+        res = fresh_class.new(model).serializable_hash
+        res.should have_key :nonexistent_attribute
+      end
+
+      it "does not expose attributes that are generated by a block but have not passed criteria" do
+        fresh_class.expose :nonexistent_attribute, :proc => lambda {|model, _|
+          "I exist, but it is not yet my time to shine"
+        }, :if => lambda { |model, _| false }
+        res = fresh_class.new(model).serializable_hash
+        res.should_not have_key :nonexistent_attribute
+      end
+
       context '#serializable_hash' do
 
         module EntitySpec
@@ -451,6 +472,63 @@ class FriendEntity < Grape::Entity
           rep.last.serializable_hash[:name].should == 'Friend 2'
         end
 
+        it "passes through the proc which returns an array of objects with custom options(:using)" do
+          module EntitySpec
+            class FriendEntity < Grape::Entity
+              root 'friends', 'friend'
+              expose :name, :email
+            end
+          end
+
+          fresh_class.class_eval do
+            expose :custom_friends, :using => EntitySpec::FriendEntity do |user, options|
+              user.friends
+            end
+          end
+
+          rep = subject.send(:value_for, :custom_friends)
+          rep.should be_kind_of Array
+          rep.reject{|r| r.is_a?(EntitySpec::FriendEntity)}.should be_empty
+          rep.first.serializable_hash.should == { :name => 'Friend 1', :email => '[email protected]'}
+          rep.last.serializable_hash.should == { :name => 'Friend 2', :email => '[email protected]'}
+        end
+        it "passes through the proc which returns single object with custom options(:using)" do
+          module EntitySpec
+            class FriendEntity < Grape::Entity
+              root 'friends', 'friend'
+              expose :name, :email
+            end
+          end
+
+          fresh_class.class_eval do
+            expose :first_friend, :using => EntitySpec::FriendEntity do |user, options|
+              user.friends.first
+            end
+          end
+
+          rep = subject.send(:value_for, :first_friend)
+          rep.should be_kind_of EntitySpec::FriendEntity
+          rep.serializable_hash.should == { :name => 'Friend 1', :email => '[email protected]'}
+        end
+        it "passes through the proc which returns empty with custom options(:using)" do
+          module EntitySpec
+            class FriendEntity < Grape::Entity
+              root 'friends', 'friend'
+              expose :name, :email
+            end
+          end
+
+          fresh_class.class_eval do
+            expose :first_friend, :using => EntitySpec::FriendEntity do |user, options|
+
+            end
+          end
+
+          rep = subject.send(:value_for, :first_friend)
+          rep.should be_kind_of EntitySpec::FriendEntity
+          rep.serializable_hash.should be_nil
+        end
+
         it 'passes through custom options' do
           module EntitySpec
             class FriendEntity < Grape::Entity