[Feat] Add the ability to change key for metadata

README.md

@@ -1233,6 +1233,65 @@ UserResource.new([user]).serialize
 
 UserResource.new([user]).serialize(meta: {foo: :bar})
 # => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"meta":{"size":1,"foo":"bar"}}'
+```
+
+You can change the key for metadata. If you change the key, it also affects the key when you pass `meta` option.
+
+```ruby
+# You can change meta key
+class UserResourceWithDifferentMetaKey
+  include Alba::Resource
+
+  root_key :user, :users
+
+  attributes :id, :name
+
+  meta :my_meta do
+    {foo: :bar}
+  end
+end
+
+UserResourceWithDifferentMetaKey.new([user]).serialize
+# => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"my_meta":{"foo":"bar"}}'
+
+UserResourceWithDifferentMetaKey.new([user]).serialize(meta: {extra: 42})
+# => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"meta":{"size":1,"extra":42}}'
+
+class UserResourceChangingMetaKeyOnly
+  include Alba::Resource
+
+  root_key :user, :users
+
+  attributes :id, :name
+
+  meta :my_meta
+end
+
+UserResourceChangingMetaKeyOnly.new([user]).serialize
+# => '{"users":[{"id":1,"name":"Masafumi OKURA"}]}'
+
+UserResourceChangingMetaKeyOnly.new([user]).serialize(meta: {extra: 42})
+# => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"my_meta":{"extra":42}}'
+```
+
+It's also possible to remove the key for metadata, resulting a flat structure.
+
+```ruby
+class UserResourceRemovingMetaKey
+  include Alba::Resource
+
+  root_key :user, :users
+
+  attributes :id, :name
+
+  meta nil
+end
+
+UserResourceRemovingMetaKey.new([user]).serialize
+# => '{"users":[{"id":1,"name":"Masafumi OKURA"}]}'
+
+UserResourceRemovingMetaKey.new([user]).serialize(meta: {extra: 42})
+# => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"extra":42}'
 
 # You can set metadata with `meta` option alone
 

lib/alba/resource.rb

@@ -22,7 +22,7 @@ module Resource
     # @private
     def self.included(base) # rubocop:disable Metrics/MethodLength
       super
-      setup_method_body = 'private def _setup;'
+      setup_method_body = +'private def _setup;'
       base.class_eval do
         # Initialize
         INTERNAL_VARIABLES.each do |name, initial|
@@ -111,13 +111,22 @@ def serialize_with(hash)
       end
 
       def hash_with_metadata(hash, meta)
-        return hash if meta.empty? && @_meta.nil?
+        return hash if meta.empty? && @_meta&.last.nil?
 
-        metadata = @_meta ? instance_eval(&@_meta).merge(meta) : meta
-        hash[:meta] = metadata
+        key, block = @_meta || :meta
+
+        if key
+          hash[key] = _metadata(block, meta)
+        else
+          _metadata(block, meta).each { |k, v| hash[k] = v }
+        end
         hash
       end
 
+      def _metadata(block, meta)
+        block ? instance_eval(&block).merge(meta) : meta
+      end
+
       def serializable_hash_for_collection
         if @_collection_key
           @object.to_h do |item|
@@ -446,8 +455,8 @@ def root_key!
       end
 
       # Set metadata
-      def meta(&block)
-        @_meta = block
+      def meta(key = :meta, &block)
+        @_meta = [key, block]
       end
 
       # Set layout

test/usecases/meta_test.rb

@@ -93,4 +93,89 @@ def test_it_includes_meta_with_given_meta_option_without_meta_dsl
       UserResourceWithoutMeta.new([@user]).serialize(meta: {class: 'MetaTest'})
     )
   end
+
+  class UserResource2
+    include Alba::Resource
+
+    root_key :user, :users
+
+    attributes :id, :name
+
+    meta :my_meta do
+      if object.is_a?(Enumerable)
+        {size: object.size}
+      else
+        {foo: :bar}
+      end
+    end
+  end
+
+  def test_changing_meta_key
+    assert_equal(
+      '{"users":[{"id":1,"name":"Masafumi OKURA"}],"my_meta":{"size":1}}',
+      UserResource2.new([@user]).serialize
+    )
+  end
+
+  def test_changing_meta_key_with_meta_ooption
+    assert_equal(
+      '{"users":[{"id":1,"name":"Masafumi OKURA"}],"my_meta":{"size":1,"extra":42}}',
+      UserResource2.new([@user]).serialize(meta: {extra: 42})
+    )
+  end
+
+  def test_changing_meta_keu_and_overriding_meta
+    assert_equal(
+      '{"users":[{"id":1,"name":"Masafumi OKURA"}],"my_meta":{"size":42}}',
+      UserResource2.new([@user]).serialize(meta: {size: 42})
+    )
+  end
+
+  class UserResource3
+    include Alba::Resource
+
+    root_key :user, :users
+
+    attributes :id, :name
+
+    meta :my_meta # Change meta key only
+  end
+
+  def test_changing_meta_key_only
+    assert_equal(
+      '{"users":[{"id":1,"name":"Masafumi OKURA"}],"my_meta":{"extra":42}}',
+      UserResource3.new([@user]).serialize(meta: {extra: 42})
+    )
+  end
+
+  def test_changing_meta_key_and_eventually_no_meta
+    assert_equal(
+      '{"users":[{"id":1,"name":"Masafumi OKURA"}]}',
+      UserResource3.new([@user]).serialize
+    )
+  end
+
+  class UserResource4
+    include Alba::Resource
+
+    root_key :user, :users
+
+    attributes :id, :name
+
+    meta nil # Do not nest meta key
+  end
+
+  def test_meta_without_nesting
+    assert_equal(
+      '{"users":[{"id":1,"name":"Masafumi OKURA"}],"extra":42}',
+      UserResource4.new([@user]).serialize(meta: {extra: 42})
+    )
+  end
+
+  def test_meta_without_nesting_but_eventually_no_meta
+    assert_equal(
+      '{"users":[{"id":1,"name":"Masafumi OKURA"}]}',
+      UserResource4.new([@user]).serialize
+    )
+  end
 end