fix incorrect model passed to serializer when fetching related object

Author: Resonance1584

lib/serialize.js

@@ -18,6 +18,7 @@ module.exports = function (app, defaults) {
       type,
       options,
       modelNamePlural,
+      relatedModel,
       relatedModelPlural,
       relations,
       model,
@@ -70,11 +71,18 @@ module.exports = function (app, defaults) {
 
     var relation = model.relations[relationName];
     if (relationName && relation) {
-      relatedModelPlural = utils.pluralForModel(relation.modelTo);
-      primaryKeyField = utils.primaryKeyForModel(relation.modelTo);
+      if (relation.polymorphic) {
+        var discriminator = utils.clone(ctx.instance)[relation.polymorphic.discriminator];
+        relatedModel = app.models[discriminator];
+      } else {
+        relatedModel = relation.modelTo;
+      }
+      relatedModelPlural = utils.pluralForModel(relatedModel);
+      primaryKeyField = utils.primaryKeyForModel(relatedModel);
 
       if (relatedModelPlural) {
         type = relatedModelPlural;
+        model = relatedModel;
       }
     }
 

lib/serializer.js

@@ -167,7 +167,6 @@ function parseRelations (data, relations, options) {
   var collection = parts[parts.length - 1];
 
   _.each(relations, function (relation, name) {
-
     var fkName = relation.keyTo;
 
     // If relation is belongsTo then fk is the other way around
@@ -187,7 +186,7 @@ function parseRelations (data, relations, options) {
       if (fkName !== options.primaryKeyField) {
         delete data[fkName];
       }
-      relationships = parseRelations(data, relation.modelTo.relations, options);
+      relationships = parseRelations(data, options.model.relations, options);
       return false;
     }
 

test/belongsToPolymorphic.test.js

@@ -75,5 +75,21 @@ describe('loopback json api belongsTo polymorphic relationships', function () {
           done();
         });
     });
+
+    it('should return the Post that this file belongs to when following the relationship link', function (done) {
+      request(app).get('/files/1')
+        .end(function (err, res) {
+          expect(err).to.equal(null);
+          expect(res.body.errors).to.equal(undefined);
+          request(app).get(res.body.data.relationships.parent.links.related.split('api')[1])
+            .end(function (err, res) {
+              expect(err).to.equal(null);
+              expect(res.body.errors).to.equal(undefined);
+              expect(res.body.data.type).to.equal('posts');
+              expect(res.body.data.id).to.equal('1');
+              done();
+            });
+        });
+    });
   });
 });