fix id property for composite ids

Signed-off-by: Clark Wang <clark.wangs@gmail.com>

lib/model-builder.js

@@ -266,7 +266,8 @@ ModelBuilder.prototype.define = function defineClass(className, properties, sett
       get: function () {
         var compositeId = {};
         var idNames = ModelClass.definition.idNames();
-        for (var p in idNames) {
+        for (var i = 0, p; i < idNames.length; i++) {
+          p = idNames[i];
           compositeId[p] = this.__data[p];
         }
         return compositeId;

test/loopback-dl.test.js

@@ -243,6 +243,19 @@ describe('ModelBuilder define model', function () {
     done(null, User);
   });
 
+  it('should define an id property for composite ids', function () {
+    var modelBuilder = new ModelBuilder();
+    var Follow = modelBuilder.define('Follow', {
+      followerId: { type: String, id: 1 },
+      followeeId: { type: String, id: 2 },
+      followAt: Date
+    });
+    var follow = new Follow({ followerId: 1, followeeId: 2 });
+
+    follow.should.have.property('id');
+    assert.deepEqual(follow.id, { followerId: 1, followeeId: 2 });
+  });
+
 });
 
 describe('DataSource ping', function() {