diff --git a/lib/datasource.js b/lib/datasource.js
index a7f9005f..be663cbf 100644
--- a/lib/datasource.js
+++ b/lib/datasource.js
@@ -310,6 +310,8 @@ function isModelClass(cls) {
     return cls.prototype instanceof ModelBaseClass;
 }
 
+DataSource.relationTypes = ['belongsTo', 'hasMany', 'hasAndBelongsToMany'];
+
 /*!
  * Define relations for the model class from the relations object
  * @param modelClass
@@ -357,7 +359,7 @@ DataSource.prototype.defineRelations = function(modelClass, relations) {
     if (relations) {
         for (var rn in relations) {
             var r = relations[rn];
-            assert(['belongsTo', 'hasMany', 'hasAndBelongsToMany'].indexOf(r.type) !== -1, "Invalid relation type: " + r.type);
+            assert(DataSource.relationTypes.indexOf(r.type) !== -1, "Invalid relation type: " + r.type);
             var targetModel = isModelClass(r.model) ? r.model : this.models[r.model];
             if (!targetModel) {
                 // The target model doesn't exist, let create a place holder for it