Provide key case translation

Author: remear

CHANGELOG.md

@@ -3,6 +3,7 @@
 Breaking changes:
 
 Features:
+- [#1574](https://github.com/rails-api/active_model_serializers/pull/1574) Provide key translation. (@remear)
 - [#1494](https://github.com/rails-api/active_model_serializers/pull/1494) Make serializers serializalbe
   (using the Attributes adapter by default). (@bf4)
 - [#1550](https://github.com/rails-api/active_model_serializers/pull/1550) Add

docs/general/configuration_options.md

@@ -2,26 +2,93 @@
 
 # Configuration Options
 
-The following configuration options can be set on `ActiveModelSerializers.config`,
-preferably inside an initializer.
+The following configuration options can be set on
+`ActiveModelSerializers.config`, preferably inside an initializer.
 
 ## General
 
-- `adapter`: The [adapter](adapters.md) to use. Possible values: `:attributes, :json, :json_api`. Default: `:attributes`.
-- `serializer_lookup_enabled`: When `false`, serializers must be explicitly specified. Default: `true`
+##### adapter
+
+The [adapter](adapters.md) to use.
+
+Possible values:
+
+- `:attributes` (default)
+- `:json`
+- `:json_api`
+
+##### serializer_lookup_enabled
+
+Enable automatic serializer lookup.
+
+Possible values:
+
+- `true` (default)
+- `false`
+
+When `false`, serializers must be explicitly specified.
+
+##### key_transform
+
+The [key transform](key_transform.md) to use.
+
+Possible values:
+
+- `:camel` - ExampleKey
+- `:camel_lower` - exampleKey
+- `:dashed` - example-key
+- `:unaltered` - the original, unaltered key
+- `nil` - use the adapter default
+
+Each adapter has a default key transform configured:
+
+- `Json` - `:unaltered`
+- `JsonApi` - `:dashed`
+
+`config.key_transform` is a global override of the adapter default. Adapters
+still prefer the render option `:key_transform` over this setting.
+
 
 ## JSON API
 
-- `jsonapi_resource_type`: Whether the `type` attributes of resources should be singular or plural. Possible values: `:singular, :plural`. Default: `:plural`.
-- `jsonapi_include_toplevel_object`: Whether to include a [top level JSON API member](http://jsonapi.org/format/#document-jsonapi-object)
-   in the response document.
-   Default: `false`.
-- Used when `jsonapi_include_toplevel_object` is `true`:
-  - `jsonapi_version`: The latest version of the spec the API conforms to.
-    Default: `'1.0'`.
-  - `jsonapi_toplevel_meta`: Optional metadata. Not included if empty.
-    Default: `{}`.
+
+##### jsonapi_resource_type
+
+Set the `type` attributes of resources to singular or plural.
+
+Possible values:
+
+- `:singular`
+- `:plural` (default)
+
+##### jsonapi_include_toplevel_object
+
+Include a [top level jsonapi member](http://jsonapi.org/format/#document-jsonapi-object)
+in the response document.
+
+Possible values:
+
+- `true`
+- `false` (default)
+
+##### jsonapi_version
+
+The latest version of the spec to which the API conforms.
+
+Default: `'1.0'`.
+
+*Used when `jsonapi_include_toplevel_object` is `true`*
+
+##### jsonapi_toplevel_meta
+
+Optional top-level metadata. Not included if empty.
+
+Default: `{}`.
+
+*Used when `jsonapi_include_toplevel_object` is `true`*
+
 
 ## Hooks
 
-To run a hook when ActiveModelSerializers is loaded, use `ActiveSupport.on_load(:action_controller) do end`
+To run a hook when ActiveModelSerializers is loaded, use
+`ActiveSupport.on_load(:action_controller) do end`

docs/general/key_transform.md

@@ -0,0 +1,34 @@
+[Back to Guides](../README.md)
+
+# Key Transforms
+
+Key transforms modify the keys in serialized responses.
+
+Provided key transforms:
+
+- `:camel` - ExampleKey
+- `:camel_lower` - exampleKey
+- `:dashed` - example-key
+- `:unaltered` - the original, unaltered key
+- `nil` - use the adapter default
+
+Key translation precedence is as follows:
+
+##### SerializableResource option
+
+`key_transform` is provided as an option via render.
+
+```render json: posts, each_serializer: PostSerializer, key_transform: :camel_lower```
+
+##### Configuration option
+
+`key_transform` is set in `ActiveModelSerializers.config.key_transform`.
+
+```ActiveModelSerializers.config.key_transform = :camel_lower```
+
+##### Adapter default
+
+Each adapter has a default key transform configured:
+
+- `Json` - `:unaltered`
+- `JsonApi` - `:dashed`

docs/general/rendering.md

@@ -79,6 +79,12 @@ PR please :)
 
 PR please :)
 
+#### key_transform
+
+```render json: posts, each_serializer: PostSerializer, key_transform: :camel_lower```
+
+See [Key Transforms](key_transforms.md) for more informaiton.
+
 #### meta
 
 A `meta` member can be used to include non-standard meta-information. `meta` can

lib/action_controller/serialization.rb

@@ -56,7 +56,9 @@ def use_adapter?
 
     [:_render_option_json, :_render_with_renderer_json].each do |renderer_method|
       define_method renderer_method do |resource, options|
-        options.fetch(:serialization_context) { options[:serialization_context] = ActiveModelSerializers::SerializationContext.new(request) }
+        options.fetch(:serialization_context) do
+          options[:serialization_context] = ActiveModelSerializers::SerializationContext.new(request, options)
+        end
         serializable_resource = get_serializer(resource, options)
         super(serializable_resource, options)
       end

lib/active_model/serializer/configuration.rb

@@ -26,6 +26,7 @@ def config.array_serializer
         # Make JSON API top-level jsonapi member opt-in
         # ref: http://jsonapi.org/format/#document-top-level
         config.jsonapi_include_toplevel_object = false
+        config.key_transform = nil
 
         config.schema_path = 'test/support/schemas'
       end

lib/active_model_serializers/adapter/base.rb

@@ -1,3 +1,5 @@
+require 'active_model_serializers/key_transform'
+
 module ActiveModelSerializers
   module Adapter
     class Base
@@ -51,6 +53,27 @@ def include_meta(json)
         json[meta_key] = meta unless meta.blank?
         json
       end
+
+      def default_key_transform
+        :unaltered
+      end
+
+      # Determines the transform to use in order of precedence:
+      #   serialization context, global config, adapter default.
+      #
+      # @param serialization_context [Object] the SerializationContext
+      # @return [Symbol] the transform to use
+      def key_transform(serialization_context)
+        serialization_context.key_transform ||
+        ActiveModelSerializers.config.key_transform ||
+        default_key_transform
+      end
+
+      def transform_key_casing!(value, serialization_context)
+        return value unless serialization_context
+        transform = key_transform(serialization_context)
+        KeyTransform.send(transform, value)
+      end
     end
   end
 end

lib/active_model_serializers/adapter/json.rb

@@ -3,7 +3,8 @@ module Adapter
     class Json < Base
       def serializable_hash(options = nil)
         options ||= {}
-        { root => Attributes.new(serializer, instance_options).serializable_hash(options) }
+        serialized_hash = { root => Attributes.new(serializer, instance_options).serializable_hash(options) }
+        transform_key_casing!(serialized_hash, options[:serialization_context])
       end
     end
   end

lib/active_model_serializers/adapter/json_api.rb

@@ -37,15 +37,20 @@ def initialize(serializer, options = {})
         @fieldset = options[:fieldset] || ActiveModel::Serializer::Fieldset.new(options.delete(:fields))
       end
 
+      def default_key_transform
+        :dashed
+      end
+
       # {http://jsonapi.org/format/#crud Requests are transactional, i.e. success or failure}
       # {http://jsonapi.org/format/#document-top-level data and errors MUST NOT coexist in the same document.}
       def serializable_hash(options = nil)
         options ||= {}
-        if serializer.success?
-          success_document(options)
-        else
-          failure_document
-        end
+        document = if serializer.success?
+                     success_document(options)
+                   else
+                     failure_document
+                   end
+        transform_key_casing!(document, options[:serialization_context])
       end
 
       # {http://jsonapi.org/format/#document-top-level Primary data}

lib/active_model_serializers/key_transform.rb

@@ -0,0 +1,40 @@
+require 'active_support/core_ext/hash/keys'
+
+module ActiveModelSerializers
+  module KeyTransform
+    module_function
+
+    # Transforms keys to UpperCamelCase or PascalCase.
+    #
+    # @example:
+    #    "some_key" => "SomeKey",
+    # @see {https://github.com/rails/rails/blob/master/activesupport/lib/active_support/inflector/methods.rb#L66-L76 ActiveSupport::Inflector.camelize}
+    def camel(hash)
+      hash.deep_transform_keys! { |key| key.to_s.camelize.to_sym }
+    end
+
+    # Transforms keys to camelCase.
+    #
+    # @example:
+    #    "some_key" => "someKey",
+    # @see {https://github.com/rails/rails/blob/master/activesupport/lib/active_support/inflector/methods.rb#L66-L76 ActiveSupport::Inflector.camelize}
+    def camel_lower(hash)
+      hash.deep_transform_keys! { |key| key.to_s.camelize(:lower).to_sym }
+    end
+
+    # Transforms keys to dashed-case.
+    # This is the default case for the JsonApi adapter.
+    #
+    # @example:
+    #    "some_key" => "some-key",
+    # @see {https://github.com/rails/rails/blob/master/activesupport/lib/active_support/inflector/methods.rb#L185-L187 ActiveSupport::Inflector.dasherize}
+    def dashed(hash)
+      hash.deep_transform_keys! { |key| key.to_s.dasherize.to_sym }
+    end
+
+    # Returns the hash unaltered
+    def unaltered(hash)
+      hash
+    end
+  end
+end

lib/active_model_serializers/serialization_context.rb

@@ -4,13 +4,14 @@ class << self
       attr_writer :url_helpers, :default_url_options
     end
 
-    attr_reader :request_url, :query_parameters
+    attr_reader :request_url, :query_parameters, :key_transform
 
     def initialize(request, options = {})
       @request_url = request.original_url[/\A[^?]+/]
       @query_parameters = request.query_parameters
       @url_helpers = options.delete(:url_helpers) || self.class.url_helpers
       @default_url_options = options.delete(:default_url_options) || self.class.default_url_options
+      @key_transform = options.delete(:key_transform)
     end
 
     def self.url_helpers