Add generateUniqueId prototype

lib/connector.js

@@ -54,6 +54,20 @@ Connector.prototype.getDefaultIdType = function(prop) {
   return String;
 };
 
+/**
+ * Generate random id.  Each data source model must override this method.
+ * @param {String} modelName Model name
+ * @returns {<model dependent>} Data type varies from model to model,
+ */
+
+Connector.prototype.generateUniqueId = function(modelName) {
+  var idType = this.getDefaultIdType && this.getDefaultIdType();
+  var isTypeFunction = (typeof idType === 'function');
+  var id = this.generateValueByColumnType ? this.generateValueByColumnType(idType) :
+    (typeof idType === 'function' ? idType() : null);
+  return id;
+};
+
 /**
  * Get the metadata for the connector
  * @returns {Object} The metadata object