Add an immutable option to JSON API resources.

Discussed here:
#343

Author: lcpriest

lib/json_api_client/errors.rb

@@ -11,6 +11,12 @@ def initialize(env, msg = nil)
     class ClientError < ApiError
     end
 
+    class ResourceImmutableError < StandardError
+      def initialize(msg = 'Resource immutable')
+        super msg
+      end
+    end
+
     class AccessDenied < ClientError
     end
 

lib/json_api_client/resource.rb

@@ -40,6 +40,11 @@ class Resource
                     instance_accessor: false
     class_attribute :add_defaults_to_changes,
                     instance_writer: false
+
+    class_attribute :_immutable,
+                    instance_writer: false,
+                    default: false
+
     self.primary_key          = :id
     self.parser               = Parsers::Parser
     self.paginator            = Paginating::Paginator
@@ -94,6 +99,18 @@ def type
         table_name
       end
 
+      # Indicates whether this resource is mutable or immutable;
+      # by default, all resources are mutable.
+      #
+      # @return [Boolean]
+      def immutable(flag = true)
+        self._immutable = flag
+      end
+
+      def inherited(subclass)
+        subclass._immutable = false
+      end
+
       # Specifies the relative path that should be used for this resource;
       # by default, this is inferred from the resource class name.
       #
@@ -215,6 +232,11 @@ def route_formatter
       # @option [Symbol] :on One of [:collection or :member] to decide whether it's a collect or member method
       # @option [Symbol] :request_method The request method (:get, :post, etc)
       def custom_endpoint(name, options = {})
+        if _immutable
+          request_method = options.fetch(:request_method, :get).to_sym
+          raise JsonApiClient::Errors::ResourceImmutableError if request_method != :get
+        end
+
         if :collection == options.delete(:on)
           collection_endpoint(name, options)
         else
@@ -440,6 +462,7 @@ def valid?(context = nil)
     # @return [Boolean] Whether or not the save succeeded
     def save
       return false unless valid?
+      raise JsonApiClient::Errors::ResourceImmutableError if _immutable
 
       self.last_result_set = if persisted?
         self.class.requestor.update(self)
@@ -471,6 +494,8 @@ def save
     #
     # @return [Boolean] Whether or not the destroy succeeded
     def destroy
+      raise JsonApiClient::Errors::ResourceImmutableError if _immutable
+
       self.last_result_set = self.class.requestor.destroy(self)
       if last_result_set.has_errors?
         fill_errors

test/unit/resource_test.rb

@@ -95,4 +95,14 @@ def test_default_params_overrideable
     assert_equal(article.type, 'Story')
   end
 
+  def test_immutable
+    Article.immutable(true)
+    article = Article.new(type: 'Story')
+    assert_raises JsonApiClient::Errors::ResourceImmutableError do
+      article.save
+    end
+  ensure
+    Article.immutable(false)
+  end
+
 end