fix relationship name for belongsTo polymorphic

Author: Resonance1584

lib/patch.js

@@ -103,7 +103,7 @@ function belongsToRemoting (relationName, relation, define) {
     },
     returns: {
       arg: 'result',
-      type: relation.modelTo.modelName,
+      type: modelName,
       root: true
     }
   }, findBelongsToRelationshipsFunc);

lib/serialize.js

@@ -83,6 +83,7 @@ module.exports = function (app, defaults) {
       requestedIncludes = ctx.req.remotingContext.args.filter.include;
     }
     options = {
+      app: app,
       model: model,
       method: ctx.method.name,
       primaryKeyField: primaryKeyField,

lib/serializer.js

@@ -195,7 +195,14 @@ function parseRelations (data, relations, options) {
     var fk = data[fkName];
 
     var fromType = utils.pluralForModel(relation.modelFrom);
-    var toType = utils.pluralForModel(relation.modelTo);
+    var toType = '';
+    if (relation.polymorphic) {
+      var discriminator = relation.polymorphic.discriminator;
+      var model = options.app.models[data[discriminator]];
+      toType = utils.pluralForModel(model);
+    } else {
+      toType = utils.pluralForModel(relation.modelTo);
+    }
 
     // Relationship `links` should always be defined unless this is a
     // relationship request

test/belongsToPolymorphic.test.js

@@ -0,0 +1,67 @@
+var request = require('supertest');
+var loopback = require('loopback');
+var expect = require('chai').expect;
+var JSONAPIComponent = require('../');
+var app;
+var ds;
+var Post;
+var File;
+
+describe('loopback json api belongsTo polymorphic relationships', function () {
+  beforeEach(function () {
+    app = loopback();
+    app.set('legacyExplorer', false);
+    ds = loopback.createDataSource('memory');
+    Post = ds.createModel('post', {
+      id: {type: Number, id: true},
+      title: String,
+      content: String
+    });
+    Post.settings.plural = 'posts';
+    app.model(Post);
+
+    File = ds.createModel('file', {
+      id: {type: Number, id: true},
+      fileName: String,
+      parentId: Number,
+      parentType: String
+    });
+    File.settings.plural = 'files';
+    File.belongsTo('parent', {
+      polymorphic: {
+        foreignKey: 'parentId',
+        discriminator: 'parentType'
+      }
+    });
+    app.model(File);
+
+    app.use(loopback.rest());
+    JSONAPIComponent(app);
+  });
+
+  describe('File belonging to a Post', function () {
+    beforeEach(function (done) {
+      Post.create({
+        title: 'Post One',
+        content: 'Content'
+      }, function (err, post) {
+        expect(err).to.equal(null);
+        File.create({
+          fileName: 'blah.jpg',
+          parentId: post.id,
+          parentType: 'post'
+        }, done);
+      });
+    });
+
+    it('should have a relationship to Post', function (done) {
+      request(app).get('/files/1')
+        .end(function (err, res) {
+          expect(err).to.equal(null);
+          expect(res.body.errors).to.equal(undefined);
+          expect(res.body.data.relationships.parent).to.be.an('object');
+          done();
+        });
+    });
+  });
+});