[Issue ruby-grape#13] Add render syntactic sugar

As in issue ruby-grape#13 an example solution provided by @jrhe an implementation
of said feature has been created.

As per the discussion in the thread this is only a helper to be able to
reach the available options provided in the active_model_serializer gem.

usage is as follows:

```ruby
get '/some_path' do
  collection = Collection.all
  render collection, { meta: { current_page: 5 }, meta_key:
    :pagination_info }
end
```

The return value would be:
`{ pagination_info: { current_page: 5 }, collection: [item, item] }`

If given without a `meta_key` it would return as:
`{ meta: { current_page: 5 }, collection: [item, item] }`

Any feedback appreciated.

@zph, @olleolleolle and @bjoska

lib/grape-active_model_serializers/endpoint_extension.rb

@@ -27,9 +27,26 @@ def serialization_scope
       end
     end
 
+    def render(resources, meta={})
+      set_meta_and_meta_key(meta)
+      resources
+    end
+
     def default_serializer_options; end
+
     def url_options; end
-  end
 
+    private
+
+    def set_meta_and_meta_key(meta)
+      if meta.has_key?(:meta)
+        Formatter::ActiveModelSerializers.meta = meta[:meta]
+        if meta.has_key?(:meta_key)
+          Formatter::ActiveModelSerializers.meta_key = meta[:meta_key]
+        end
+      end
+    end
+
+  end
   Endpoint.send(:include, EndpointExtension)
 end

lib/grape-active_model_serializers/formatter.rb

@@ -20,7 +20,42 @@ def fetch_serializer(resource, env)
             # ensure we have an root to fallback on
             endpoint.controller_name = default_root(endpoint)
           end
-          ::ActiveModel::Serializer.build_json(endpoint, resource, options)
+
+          ::ActiveModel::Serializer.build_json(endpoint,
+                                               resource,
+                                               options.merge(other_options)
+                                              )
+        end
+
+        def other_options
+          options = {}
+          if @meta_content_items
+            meta_option = @meta_content_items[:meta]
+            @meta_content_items.delete(:meta)
+            options[:meta] = meta_option if meta_option
+            if @meta_key
+             key_option = @meta_key[:meta_key]
+              @meta_key.delete(:meta_key)
+              options[:meta_key] = key_option if key_option
+            end
+          end
+          options
+        end
+
+        def meta
+          @meta_content_items || {}
+        end
+
+        def meta=(meta_content)
+          @meta_content_items = { meta: meta_content } if meta_content
+        end
+
+        def meta_key
+          @meta_key || {}
+        end
+
+        def meta_key=(key)
+          @meta_key = { meta_key: key } if key
         end
 
         def build_options_from_endpoint(endpoint)

spec/features/grape-active_model_serializers/render_spec.rb

@@ -0,0 +1,66 @@
+require 'spec_helper'
+require 'support/models/user'
+require 'support/serializers/user_serializer'
+require 'grape-active_model_serializers'
+require 'securerandom'
+
+describe '#render' do
+  let(:app) { Class.new(Grape::API) }
+
+  before do
+    app.format :json
+    app.formatter :json, Grape::Formatter::ActiveModelSerializers
+  end
+
+  def get_resource_with(meta)
+    url = "/#{SecureRandom.hex}"
+    app.get(url) do
+      user = User.new(first_name: 'Jeff')
+      render [user, user], meta
+    end
+    get url
+    JSON.parse last_response.body
+  end
+
+  context 'with meta key' do
+    it 'includes meta key and content' do
+      result = get_resource_with({ meta: { total: 2 }})
+      expect(result).to have_key('meta')
+      expect(result.fetch('meta')).to eq({ 'total' => 2 })
+    end
+  end
+
+  context 'with a custom meta_key' do
+
+    it 'includes the custom meta key name' do
+      result = get_resource_with({ meta: { total: 2 }, meta_key: :custom_key_name })
+      expect(result).to have_key('custom_key_name')
+      expect(result.fetch('custom_key_name')).to eq({ 'total' => 2 })
+    end
+
+    it 'ignores a lonely meta_key' do
+      result = get_resource_with({ meta_key: :custom_key_name })
+      expect(result).not_to have_key('meta')
+      expect(result).not_to have_key('custom_key_name')
+    end
+  end
+
+  context 'junk keys' do
+
+    it 'ignores junk keys' do
+      result = get_resource_with({ junk_key: { total: 2 } })
+      expect(result).not_to have_key('junk_key')
+    end
+
+    it 'ignores empty meta_key' do
+      result = get_resource_with({ meta: { total: 2 }, meta_key: nil })
+      expect(result).to have_key('meta')
+    end
+
+    it 'ignores empty meta' do
+      result = get_resource_with({ meta: nil })
+      expect(result).not_to have_key('meta')
+    end
+
+  end
+end

spec/grape-active_model_serializers/endpoint_extension_spec.rb

@@ -0,0 +1,39 @@
+require 'spec_helper'
+
+describe 'Grape::EndpointExtension' do
+
+  subject { Grape::Endpoint.new(nil, {path: '/', method: 'foo'}) }
+
+  let(:serializer) { Grape::Formatter::ActiveModelSerializers }
+
+  let(:user) do
+               Object.new do
+                 def name
+                   'sven'
+                 end
+               end
+             end
+
+  let(:users) { [user, user] }
+
+  describe "#render" do
+    it { should respond_to(:render) }
+    let (:meta_content) { { total: 2 } }
+    let (:meta_full) { { meta: meta_content } }
+    context 'supplying meta' do
+      it 'passes through the Resource and uses given meta settings' do
+        expect(serializer).to receive(:meta=).with(meta_content)
+        expect(subject.render(users, meta_full)).to eq(users)
+      end
+    end
+    context 'supplying meta and key' do
+      let (:meta_key) { { meta_key: :custom_key_name } }
+      it 'passes through the Resource and uses given meta settings' do
+        expect(serializer).to receive(:meta=).with(meta_content)
+        expect(serializer).to receive(:meta_key=).with(meta_key[:meta_key])
+        expect(subject.render(users, meta_full.merge(meta_key))).to eq(users)
+      end
+    end
+  end
+
+end

spec/grape-active_model_serializers/formatter_spec.rb

@@ -2,5 +2,33 @@
 require 'grape-active_model_serializers/formatter'
 
 describe Grape::Formatter::ActiveModelSerializers do
+  subject { Grape::Formatter::ActiveModelSerializers }
+  it { should respond_to(:meta) }
+  it { should respond_to(:meta=) }
+  it { should respond_to(:meta_key) }
+  it { should respond_to(:meta_key=) }
 
+  context '#meta' do
+    it 'will silently accept falsy input but return empty Hash' do
+      subject.meta = nil
+      expect(subject.meta).to eq({})
+    end
+
+    it 'will wrap valid input in the meta: {} wrapper' do
+      subject.meta = { total: 2 }
+      expect(subject.meta).to eq({ meta: { total: 2 } })
+    end
+  end
+
+  context '#meta_key' do
+    it 'will silently accept falsy input but return empty Hash' do
+      subject.meta_key = nil
+      expect(subject.meta_key).to eq({})
+    end
+
+    it 'will wrap valid input in the meta_key: {} wrapper' do
+      subject.meta_key = :custom_key_name
+      expect(subject.meta_key).to eq({ meta_key: :custom_key_name })
+    end
+  end
 end