Created _id cannot be equal to another id

lib/datastore.js

@@ -289,6 +289,18 @@ Datastore.prototype._insert = function (newDoc, cb) {
   });
 };
 
+/**
+ * Create a new _id that's not already in use
+ */
+Datastore.prototype.createNewId = function () {
+  var tentativeId = customUtils.uid(16);
+  // Try as many times as needed to get an unused _id. As explained in customUtils, the probability of this ever happening is extremely small, so this is O(1)
+  if (this.indexes._id.getMatching(tentativeId).length > 0) {
+    tentativeId = this.createNewId();
+  }
+  return tentativeId;
+};
+
 /**
  * Prepare a document (or array of documents) to be inserted in a database
  * @api private
@@ -300,7 +312,7 @@ Datastore.prototype.prepareDocumentForInsertion = function (newDoc) {
     preparedDoc = [];
     newDoc.forEach(function (doc) { preparedDoc.push(self.prepareDocumentForInsertion(doc)); });
   } else {
-    newDoc._id = newDoc._id || customUtils.uid(16);
+    newDoc._id = newDoc._id || this.createNewId();
     preparedDoc = model.deepCopy(newDoc);
     model.checkObject(preparedDoc);
   }
@@ -578,4 +590,5 @@ Datastore.prototype.remove = function () {
 
 
 
+
 module.exports = Datastore;