Support lowerCamel key format

README.md

@@ -226,6 +226,23 @@ def default_serializer_options
 end
 ```
 
+## Changing the Key Format
+
+You can specify that serializers use the lower-camel key format at the config, class or instance level.
+
+```ruby
+
+ActiveModel::Serializer.setup do |config|
+  config.key_format = :lower_camel
+end
+
+class BlogLowerCamelSerializer < ActiveModel::Serializer 
+  format_keys :lower_camel
+end
+
+BlogSerializer.new(object, key_format: :lower_camel)
+```
+
 ## Getting the old version
 
 If you find that your project is already relying on the old rails to_json

lib/active_model/array_serializer.rb

@@ -20,8 +20,9 @@ module ActiveModel
       @meta            = options[@meta_key]
       @each_serializer = options[:each_serializer]
       @resource_name   = options[:resource_name]
+      @key_format      = options[:key_format]
     end
-    attr_accessor :object, :scope, :root, :meta_key, :meta
+    attr_accessor :object, :scope, :root, :meta_key, :meta, :key_format
 
     def json_key
       if root.nil?
@@ -33,7 +34,7 @@ module ActiveModel
 
     def serializer_for(item)
       serializer_class = @each_serializer || Serializer.serializer_for(item) || DefaultSerializer
-      serializer_class.new(item, scope: scope)
+      serializer_class.new(item, scope: scope, key_format: key_format)
     end
 
     def serializable_object

lib/active_model/serializer.rb

@@ -38,6 +38,11 @@ end
         WARN
       end
 
+      def format_keys(format)
+        @key_format = format
+      end
+      attr_reader :key_format
+
       if RUBY_VERSION >= '2.0'
         def serializer_for(resource)
           if resource.respond_to?(:to_ary)
@@ -110,6 +115,7 @@ end
       @wrap_in_array = options[:_wrap_in_array]
       @only          = Array(options[:only]) if options[:only]
       @except        = Array(options[:except]) if options[:except]
+      @key_format    = options[:key_format]
     end
     attr_accessor :object, :scope, :root, :meta_key, :meta
 
@@ -190,10 +196,35 @@ end
       end
     end
 
+    def key_format
+      @key_format || self.class.key_format || CONFIG.key_format
+    end
+
+    def format_key(key)
+      if key_format == :lower_camel
+        key.to_s.camelize(:lower)
+      else
+        key
+      end
+    end
+
+    def convert_keys(hash)
+      Hash[hash.map do |k,v|
+        key = if k.is_a?(Symbol)
+          format_key(k).to_sym
+        else
+          format_key(k)
+        end
+
+        [key ,v]
+      end]
+    end
+
     def serializable_object(options={})
       return @wrap_in_array ? [] : nil if @object.nil?
       hash = attributes
       hash.merge! associations
+      hash = convert_keys(hash) if key_format.present?
       @wrap_in_array ? [hash] : hash
     end
     alias_method :serializable_hash, :serializable_object

lib/active_model/serializer/associations.rb

@@ -15,6 +15,7 @@ module ActiveModel
         @options       = options
         self.embed     = options.fetch(:embed) { CONFIG.embed }
         @embed_in_root = options.fetch(:embed_in_root) { options.fetch(:include) { CONFIG.embed_in_root } }
+        @key_format    = options.fetch(:key_format) { CONFIG.key_format }
         @embed_key     = options[:embed_key] || :id
         @key           = options[:key]
         @embedded_key  = options[:root] || name
@@ -24,7 +25,7 @@ module ActiveModel
       end
 
       attr_reader :name, :embed_ids, :embed_objects
-      attr_accessor :embed_in_root, :embed_key, :key, :embedded_key, :root_key, :serializer_from_options, :options
+      attr_accessor :embed_in_root, :embed_key, :key, :embedded_key, :root_key, :serializer_from_options, :options, :key_format
       alias embed_ids? embed_ids
       alias embed_objects? embed_objects
       alias embed_in_root? embed_in_root

test/fixtures/poro.rb

@@ -35,6 +35,9 @@ end
 class Comment < Model
 end
 
+class Blog < Model
+end
+
 ###
 ## Serializers
 ###
@@ -62,3 +65,11 @@ end
 class CommentSerializer < ActiveModel::Serializer
   attributes :content
 end
+
+class BlogSerializer < ActiveModel::Serializer
+  attributes :name, :display_name
+end
+
+class BlogLowerCamelSerializer < BlogSerializer
+  format_keys :lower_camel
+end

test/unit/active_model/array_serializer/key_format_test.rb

@@ -0,0 +1,18 @@
+require 'test_helper'
+
+module ActiveModel
+  class ArraySerializer
+    class KeyFormatTest < Minitest::Test
+      def test_array_serializer_pass_options_to_items_serializers
+        array = [Blog.new({ name: 'Name 1', display_name: 'Display Name 1'}),
+                 Blog.new({ name: 'Name 2', display_name: 'Display Name 2'})]
+        serializer = ArraySerializer.new(array, key_format: :lower_camel)
+
+        expected = [{ name: 'Name 1', displayName: 'Display Name 1' },
+                    { name: 'Name 2', displayName: 'Display Name 2' }]
+
+        assert_equal expected, serializer.serializable_array
+      end
+    end
+  end
+end

test/unit/active_model/serializer/config_test.rb

@@ -67,6 +67,7 @@ module ActiveModel
         def test_apply_config_to_associations
           CONFIG.embed     = :ids
           CONFIG.embed_in_root = true
+          CONFIG.key_format = :lower_camel
 
           association = PostSerializer._associations[:comments]
           old_association = association.dup
@@ -76,6 +77,7 @@ module ActiveModel
           assert association.embed_ids?
           assert !association.embed_objects?
           assert association.embed_in_root
+          assert_equal :lower_camel, association.key_format
         ensure
           PostSerializer._associations[:comments] = old_association
           CONFIG.clear

test/unit/active_model/serializer/key_format_test.rb

@@ -0,0 +1,25 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class KeyFormatTest < Minitest::Test
+      def test_lower_camel_format_option
+        object     = Blog.new({ name: 'Name 1', display_name: 'Display Name 1'})
+        serializer = BlogSerializer.new(object, key_format: :lower_camel)
+
+        expected = { name: 'Name 1', displayName: 'Display Name 1' }
+
+        assert_equal expected, serializer.serializable_object
+      end
+
+      def test_lower_camel_format_serializer
+        object     = Blog.new({ name: 'Name 1', display_name: 'Display Name 1'})
+        serializer = BlogLowerCamelSerializer.new(object)
+
+        expected = { name: 'Name 1', displayName: 'Display Name 1' }
+
+        assert_equal expected, serializer.serializable_object
+      end
+    end
+  end
+end