updated FAQ to introduce the resolution of the problem for id and etag with $oid attribute

Author: antonio.gallo

README.md

@@ -76,6 +76,8 @@ You can also **check out [a video introduction of a talk I gave at Devoxx France
     - [Can it be used in $routeProvider.resolve?](#can-it-be-used-in-routeproviderresolve)
     - [My response is actually wrapped with some metadata. How do I get the data in that case?](#my-response-is-actually-wrapped-with-some-metadata-how-do-i-get-the-data-in-that-case)
     - [I use Mongo and the ID of the elements is _id not id as the default. Therefore requests are sent to undefined routes](#i-use-mongo-and-the-id-of-the-elements-is-_id-not-id-as-the-default-therefore-requests-are-sent-to-undefined-routes)
+    - [I use Mongo and the ID of the elements is `_id` and is encapsulated inside the $oid attribute](#i-use-mongo-and-the-etag-of-the-elements-is-_etag-and-is-encapsulated-inside-the-oid-attribute)
+    - [I use Mongo and the ETag of the elements is `_etag` and is encapsulated inside the $oid attribute](#i-use-mongo-and-the-etag-of-the-elements-is-_etag-and-is-encapsulated-inside-the-oid-attribute)
     - [What if each of my models has a different ID name like CustomerID for Customer](#what-if-each-of-my-models-has-a-different-id-name-like-customerid-for-customer)
     - [How do I handle CRUD operations in a List returned by Restangular?](#how-do-i-handle-crud-operations-in-a-list-returned-by-restangular)
     - [When I set baseUrl with a port, it's stripped out.](#when-i-set-baseurl-with-a-port-its-stripped-out)
@@ -1151,6 +1153,26 @@ RestangularProvider.setRestangularFields({
 });
 ````
 
+#### **I use Mongo and the ID of the elements is `_id` and is encapsulated inside the $oid attribute**
+
+What you need to do is to configure the `RestangularFields` and set the `id` field to `_id.$oid`. Let's see how:
+
+````javascript
+RestangularProvider.setRestangularFields({
+  id: "_id.$oid"
+});
+````
+
+#### **I use Mongo and the ETag of the elements is `_etag` and is encapsulated inside the $oid attribute**
+
+What you need to do is to configure the `RestangularFields` and set the `etag` field to `_etag.$oid`. Let's see how:
+
+````javascript
+RestangularProvider.setRestangularFields({
+  etag: "_etag.$oid"
+});
+````
+
 #### **What if each of my models has a different ID name like CustomerID for Customer**
 
 In some cases, people have different ID name for each entity. For example, they have CustomerID for customer and EquipmentID for Equipment. If that's the case, you can override Restangular's getIdFromElem. For that, you need to do: