add data option on relationships

README.md

@@ -45,6 +45,7 @@ Serializer.register(type, options);
     * **type**: A _string_ or a _function_ `function(relationshipData, data) { ... }` for the type to use for serializing the relationship (type need to be register).
     * **alternativeKey** (optional): An alternative key (string or path) to use if relationship key not exist (example: 'author_id' as an alternative key for 'author' relationship). See [issue #12](https://github.com/danivek/json-api-serializer/issues/12).
     * **schema** (optional): A custom schema for serializing the relationship. If no schema define, it use the default one.
+    * **data** (optional): A _function_ `function(data) { ... }` that returns the data to serialize for the relationship.
     * **links** (optional): Describes the links for the relationship. It can be:
       * An _object_ (values can be string or function).
       * A _function_ with one argument `function(data) { ... }` or with two arguments `function(data, extraData) { ... }`

lib/JSONAPISerializer.js

@@ -716,13 +716,17 @@ module.exports = class JSONAPISerializer {
         relationshipKey = relationshipOptions.alternativeKey;
       }
 
+      const dataFn = relationshipOptions.data
+        ? relationshipOptions.data
+        : (relationshipData) => relationshipData;
+
       const serializeRelationship = {
         links: this.processOptionsValues(data, extraData, relationshipOptions.links),
         meta: this.processOptionsValues(data, extraData, relationshipOptions.meta),
         data: this.serializeRelationship(
           relationshipOptions.type,
           relationshipOptions.schema,
-          get(data, relationshipKey),
+          dataFn(get(data, relationshipKey)),
           included,
           data,
           extraData,
@@ -996,6 +1000,7 @@ module.exports = class JSONAPISerializer {
  * @property {string|Function} type a string or a function for the type to use for serializing the relationship (type need to be register)
  * @property {string} [alternativeKey] an alternative key (string or path) to use if relationship key not exist (example: 'author_id' as an alternative key for 'author' relationship)
  * @property {string} [schema] a custom schema for serializing the relationship. If no schema define, it use the default one.
+ * @property {Function} [data] a function that returns the data to serialize for the relationship
  * @property {Function|object} [links] describes the links for the relationship
  * @property {Function|object} [meta] describes meta that contains non-standard meta-information about the relationship
  * @property {Function} [deserialize] describes the function which should be used to deserialize a related property which is not included in the JSON:API document

lib/validator.js

@@ -102,6 +102,9 @@ function validateOptions(options) {
 
     if (relationships[key].deserialize && typeof relationships[key].deserialize !== 'function')
       throw new Error(`option 'deserialize' for relationship '${key}' must be a function`);
+
+    if (relationships[key].data && typeof relationships[key].data !== 'function')
+      throw new Error(`option 'data' for relationship '${key}' must be a function`);
   });
 
   return options;

test/unit/JSONAPISerializer.test.js

@@ -644,6 +644,37 @@ describe('JSONAPISerializer', function() {
       expect(serializedRelationships.author).to.have.property('links').to.be.undefined;
       done();
     });
+
+    it('should return relationships with data option', function(done) {
+      const Serializer = new JSONAPISerializer();
+
+      Serializer.register('article', {
+        relationships: {
+          comments: {
+            type: 'comment',
+            data: (data) => data.data
+          }
+        }
+      });
+      Serializer.register('comment');
+
+      const serializedRelationships = Serializer.serializeRelationships({
+        id: '1',
+        comments: {
+          total: 2,
+          data: [{id: '1', title: 'comment 1'}, {id: '2', title: 'comment 2'}]
+        }
+      }, Serializer.schemas.article.default);
+      console.log(JSON.stringify(serializedRelationships, null, 2));
+      expect(serializedRelationships).to.have.property('comments');
+      expect(serializedRelationships.comments).to.have.property('data');
+      expect(serializedRelationships.comments.data).to.be.instanceof(Array).to.have.length(2);
+      expect(serializedRelationships.comments.data[0]).to.have.property('type').to.eql('comment');
+      expect(serializedRelationships.comments.data[0]).to.have.property('id').to.be.a('string').to.eql('1');
+      expect(serializedRelationships.comments.data[1]).to.have.property('id').to.be.a('string').to.eql('2');
+      expect(serializedRelationships.comments).to.have.property('links').to.be.undefined;
+      done();
+    });
   });
 
   describe('serializeAttributes', function() {

test/unit/validator.test.js

@@ -291,5 +291,20 @@ describe('validator', function () {
 
       done();
     });
+
+    it('incorrect data on relationship', (done) => {
+      expect(function () {
+        validator.validateOptions({
+          relationships: {
+            test: {
+              type: 'test',
+              data: 'test',
+            },
+          },
+        });
+      }).to.throw(Error, "option 'data' for relationship 'test' must be a function");
+
+      done();
+    });
   });
 });