Prefer resource method

.rubocop.yml

@@ -119,7 +119,7 @@ Style/InlineComment:
   Enabled: false
 
 Style/MethodCallWithArgsParentheses:
-  AllowedMethods: ['require', 'require_relative', 'include', 'extend', 'puts', 'p', 'warn', 'raise', 'send', 'public_send']
+  AllowedMethods: ['require', 'require_relative', 'include', 'extend', 'puts', 'p', 'warn', 'raise', 'send', 'public_send', 'alias_method']
   Exclude:
     # There are so many `attributes` call without parenthese and that's absolutely fine
     - 'test/**/*.rb'

README.md

@@ -269,6 +269,72 @@ class UserResource
 end
 ```
 
+#### Prefer methods on resource
+
+By default, Alba prefers methods on the object to methods on the resource. This means if you have a following situation:
+
+```ruby
+class User
+  attr_accessor :id, :name, :email
+
+  def initialize(id, name, email)
+    @id = id
+    @name = name
+    @email = email
+  end
+
+  def name_with_email
+    "dummy!"
+  end
+end
+
+class UserResource
+  include Alba::Resource
+
+  root_key :user, :users # Later is for plural
+
+  attributes :id, :name, :name_with_email
+
+  # Same method exists in `User` class!
+  # This is not called
+  def name_with_email(user)
+    "#{user.name}: #{user.email}"
+  end
+end
+
+user = User.new(1, 'Masafumi OKURA', '[email protected]')
+UserResource.new(user).serialize
+# => '{"user":{"id":1,"name":"Masafumi OKURA","name_with_email":"dummy!"}}'
+```
+
+You can see that `name_with_email` is now `dummy!` from `User#name_with_email`. You cna change this behavior by using `prefer_resource_method!` DSL in a resource class:
+
+```ruby
+# With the same `User` class
+
+class UserResource
+  include Alba::Resource
+
+  prefer_resource_method! # This line is important
+
+  root_key :user, :users # Later is for plural
+
+  attributes :id, :name, :name_with_email
+
+  # Same method exists in `User` class!
+  # But now this is called!
+  def name_with_email(user)
+    "#{user.name}: #{user.email}"
+  end
+end
+
+user = User.new(1, 'Masafumi OKURA', '[email protected]')
+UserResource.new(user).serialize
+# => '{"user":{"id":1,"name":"Masafumi OKURA","name_with_email":"Masafumi OKURA: [email protected]"}}'
+```
+
+The next major version of Alba will change this default behavior to prefer resource methods. In case you want to preserve current behavior, there's `prefer_object_method!` DSL, which does that.
+
 #### Params
 
 You can pass a Hash to the resource for internal use. It can be used as "flags" to control attribute content.

lib/alba/resource.rb

@@ -265,12 +265,23 @@ def fetch_attribute(obj, key, attribute) # rubocop:disable Metrics/CyclomaticCom
         value.nil? && nil_handler ? instance_exec(obj, key, attribute, &nil_handler) : value
       end
 
+      # TODO: from version 3, `_fetch_attribute_from_resource_first` is default
       def fetch_attribute_from_object_and_resource(obj, attribute)
+        _fetch_attribute_from_object_first(obj, attribute)
+      end
+
+      def _fetch_attribute_from_object_first(obj, attribute)
         obj.__send__(attribute)
       rescue NoMethodError
         __send__(attribute, obj)
       end
 
+      def _fetch_attribute_from_resource_first(obj, attribute)
+        __send__(attribute, obj)
+      rescue NoMethodError
+        obj.__send__(attribute)
+      end
+
       def nil_handler
         @_on_nil
       end
@@ -510,6 +521,16 @@ def helper(mod = @_helper || Module.new, &block)
         extend mod
         @_helper = mod
       end
+
+      # DSL for alias, purely for readability
+      def prefer_resource_method!
+        alias_method :fetch_attribute_from_object_and_resource, :_fetch_attribute_from_resource_first
+      end
+
+      # DSL for alias, purely for readability
+      def prefer_object_method!
+        alias_method :fetch_attribute_from_object_and_resource, :_fetch_attribute_from_object_first
+      end
     end
   end
 end

test/usecases/object_method_and_resource_method_test.rb

@@ -0,0 +1,73 @@
+require_relative '../test_helper'
+
+class ObjectMethodAndResourceMethodTest < Minitest::Test
+  class Foo
+    attr_reader :id
+    def initialize(id)
+      @id = id
+    end
+  end
+
+  def setup
+    @foo = Foo.new(1)
+  end
+
+  class FooResource
+    include Alba::Resource
+
+    prefer_resource_method!
+
+    attributes :id
+
+    def id(_)
+      42
+    end
+  end
+
+  def test_prefer_resource_method
+    assert_equal '{"id":42}', FooResource.new(@foo).serialize
+  end
+
+  class FooResource2
+    include Alba::Resource
+
+    prefer_object_method!
+
+    attributes :id
+
+    def id(_)
+      42
+    end
+  end
+
+  def test_prefer_object_method
+    assert_equal '{"id":1}', FooResource2.new(@foo).serialize
+  end
+
+  class FooResource3
+    include Alba::Resource
+
+    attributes :id
+
+    def id(_)
+      42
+    end
+  end
+
+  # TODO: perfer resource method by default from version 3
+  def test_default_behavior
+    assert_equal '{"id":1}', FooResource3.new(@foo).serialize
+  end
+
+  class FooResource4
+    include Alba::Resource
+
+    prefer_resource_method!
+
+    attributes :id
+  end
+
+  def test_prefer_resource_method_but_it_is_not_there
+    assert_equal '{"id":1}', FooResource4.new(@foo).serialize
+  end
+end