Deserialize function for relationships

README.md

@@ -52,6 +52,8 @@ Serializer.register(type, options);
     * **meta** (optional): Describes meta that contains non-standard meta-information about 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) { ... }`
+    * **deserialize** (optional): Describes the function which should be used to deserialize a related property which is not included in the JSON:API document. It should be:
+      * A _function_ with one argument `function(data) { ... }`which defines the format to which a relation should be deserialized. By default, the ID of the related object is returned, which would be equal to `function(data) {return data.id}`. See [issue #65](https://github.com/danivek/json-api-serializer/issues/65).
 * **convertCase** (optional): Case conversion for serializing data. Value can be : `kebab-case`, `snake_case`, `camelCase`
 
 **Deserialization options:**

lib/JSONAPISerializer.js

@@ -61,6 +61,7 @@ module.exports = class JSONAPISerializer {
         schema: joi.string().default('default'),
         links: joi.alternatives([joi.func(), joi.object()]).default({}),
         meta: joi.alternatives([joi.func(), joi.object()]).default({}),
+        deserialize: joi.func(),
       })).default({}),
       topLevelLinks: joi.alternatives([joi.func(), joi.object()]).default({}),
       topLevelMeta: joi.alternatives([joi.func(), joi.object()]).default({}),
@@ -487,21 +488,27 @@ module.exports = class JSONAPISerializer {
         if (resourceOpts.relationships[relationshipKey] && resourceOpts.relationships[relationshipKey].alternativeKey) {
           relationshipKey = resourceOpts.relationships[relationshipKey].alternativeKey;
         }
+        const deserializeFunction = (relationshipData) => {
+          if (resourceOpts.relationships[relationshipKey] && resourceOpts.relationships[relationshipProperty].deserialize) {
+            return resourceOpts.relationships[relationshipProperty].deserialize(relationshipData);
+          }
+          return relationshipData.id;
+        };
 
         if (relationship.data !== undefined) {
           if (Array.isArray(relationship.data)) {
             // Array data
             _set(deserializedData, relationshipKey, relationship.data.map(d => (included
               ? this.deserializeIncluded(d.type, d.id, resourceOpts.relationships[relationshipProperty], included)
-              : d.id)));
+              : deserializeFunction(d))));
           } else if (relationship.data === null) {
             // null data
             _set(deserializedData, relationshipKey, null);
           } else {
             // Object data
             _set(deserializedData, relationshipKey, included
               ? this.deserializeIncluded(relationship.data.type, relationship.data.id, resourceOpts.relationships[relationshipProperty], included)
-              : relationship.data.id);
+              : deserializeFunction(relationship.data));
           }
         }
       });

test/unit/JSONAPISerializer.test.js

@@ -1520,6 +1520,43 @@ describe('JSONAPISerializer', function() {
       done();
     });
 
+    it('should deserialize with \'deserialize\' option as a function', function(done) {
+      const Serializer = new JSONAPISerializer();
+      Serializer.register('articles', {
+        relationships: {
+          author: {
+            type: 'people',
+            deserialize: (data) => ({id: data.id, type: data.type})
+          }
+        }
+      });
+
+      const data = {
+        data: {
+          type: 'article',
+          id: '1',
+          attributes: {
+            title: 'JSON API paints my bikeshed!',
+            body: 'The shortest article. Ever.',
+            created: '2015-05-22T14:56:29.000Z'
+          },
+          relationships: {
+            author: {
+              data: {
+                type: 'people',
+                id: '1'
+              }
+            }
+          }
+        }
+      };
+
+      const deserializedData = Serializer.deserialize('articles', data);
+      expect(deserializedData.author).to.have.property('id');
+      expect(deserializedData.author).to.have.property('type');
+      done();
+    })
+
     it('should deserialize with \'unconvertCase\' options', function(done) {
       const Serializer = new JSONAPISerializer();
       Serializer.register('articles', {