Improve handling for nil relationship links.

Author: fotinakis

README.md

@@ -155,11 +155,11 @@ By default the serializer looks for the same name of the attribute on the object
   attribute :content do
     object.body
   end
-  
+
   has_one :comment do
     Comment.where(post: object).take!
   end
-  
+
   has_many :authors do
     Author.where(post: object)
   end
@@ -223,6 +223,8 @@ def relationship_related_link(attribute_name)
 end
 ```
 
+If you override `self_link`, `relationship_self_link`, or `relationship_related_link` to return `nil`, the link will be excluded from the serialized object.
+
 ## Relationships
 
 You can easily specify relationships with the `has_one` and `has_many` directives.

lib/jsonapi-serializers/serializer.rb

@@ -86,12 +86,14 @@ def relationships
         # Merge in data for has_one relationships.
         has_one_relationships.each do |attribute_name, object|
           formatted_attribute_name = format_name(attribute_name)
-          data[formatted_attribute_name] = {
-            'links' => {
-              'self' => relationship_self_link(attribute_name),
-              'related' => relationship_related_link(attribute_name),
-            },
-          }
+
+          data[formatted_attribute_name] = {}
+          links_self = relationship_self_link(attribute_name)
+          links_related = relationship_related_link(attribute_name)
+          data[formatted_attribute_name]['links'] = {} if links_self || links_related
+          data[formatted_attribute_name]['links']['self'] = links_self if links_self
+          data[formatted_attribute_name]['links']['related'] = links_related if links_related
+
           if @_include_linkages.include?(formatted_attribute_name)
             if object.nil?
               # Spec: Resource linkage MUST be represented as one of the following:
@@ -113,12 +115,14 @@ def relationships
         # Merge in data for has_many relationships.
         has_many_relationships.each do |attribute_name, objects|
           formatted_attribute_name = format_name(attribute_name)
-          data[formatted_attribute_name] = {
-            'links' => {
-              'self' => relationship_self_link(attribute_name),
-              'related' => relationship_related_link(attribute_name),
-            },
-          }
+
+          data[formatted_attribute_name] = {}
+          links_self = relationship_self_link(attribute_name)
+          links_related = relationship_related_link(attribute_name)
+          data[formatted_attribute_name]['links'] = {} if links_self || links_related
+          data[formatted_attribute_name]['links']['self'] = links_self if links_self
+          data[formatted_attribute_name]['links']['related'] = links_related if links_related
+
           # Spec: Resource linkage MUST be represented as one of the following:
           # - an empty array ([]) for empty to-many relationships.
           # - an array of linkage objects for non-empty to-many relationships.

spec/serializer_spec.rb

@@ -107,6 +107,27 @@ def serialize_primary(object, options = {})
           },
         })
       end
+      it 'does not include links if relationship_self_link and relationship_related_link are nil' do
+        post = create(:post)
+        primary_data = serialize_primary(post, {serializer: MyApp::PostSerializerWithoutLinks})
+        expect(primary_data).to eq({
+          'id' => '1',
+          'type' => 'posts',
+          'attributes' => {
+            'title' => 'Title for Post 1',
+            'long-content' => 'Body for Post 1',
+          },
+          'links' => {
+            'self' => '/posts/1',
+          },
+          # This is technically invalid since relationships MUST contain at least one of links,
+          # data, or meta, but we leave that up to the user.
+          'relationships' => {
+            'author' => {},
+            'long-comments' => {},
+          },
+        })
+      end
     end
     context 'with linkage includes' do
       it 'can serialize primary data for a null to-one relationship' do

spec/support/serializers.rb

@@ -64,6 +64,7 @@ def type
 
   class PostSerializerWithMetadata
     include JSONAPI::Serializer
+    include JSONAPI::Serializer
 
     attribute :title
     attribute :long_content do
@@ -83,8 +84,6 @@ def meta
   end
 
   class PostSerializerWithContextHandling < SimplestPostSerializer
-    include JSONAPI::Serializer
-
     attribute :body, if: :show_body?, unless: :hide_body?
 
     def show_body?
@@ -96,6 +95,26 @@ def hide_body?
     end
   end
 
+  class PostSerializerWithoutLinks
+    include JSONAPI::Serializer
+
+    attribute :title
+    attribute :long_content do
+      object.body
+    end
+
+    has_one :author
+    has_many :long_comments
+
+    def relationship_self_link(attribute_name)
+      nil
+    end
+
+    def relationship_related_link(attribute_name)
+      nil
+    end
+  end
+
   class EmptySerializer
     include JSONAPI::Serializer
   end