Question: I have a collection that fetches models from server.

This works, now I want to grab a model by its id with `MyCollection.at(0)` and I get:

```
child
_changes: Array[0]
_changing: false
_currentAttributes: Object
_events: Object
_hasComputed: true
_pending: false
_previousAttributes: Object
attributes: Object
_id: "50ef7a63b2a53d17fe000001"
author_name: "author name"
bookmark: ""
info: "bookmark description"
__proto__: Object
changed: Object
cid: "c26"
collection: child
view: child
__proto__: Surrogate

```

If I try to get the model by its id i get:

```
MyCollection.get("50ef7a63b2a53d17fe000001")
=> undefined

MyColleciton.get({_id:"50ef7a63b2a53d17fe000001"})
=> undefined

MyCollection.get({'_id':"50ef7a63b2a53d17fe000001"})
=> undefined

```

I don't get that - the docs say clearly that the `.get()` method will return the model if a model with the given id exists in that collection.

Answer: 
Have you set [`Model.idAttribute`](http://backbonejs.org/#Model-idAttribute) on the Model?

```
var Model = Backbone.Model.extend({
    idAttribute:"_id"
});

```

By default Backbone expects the id property be called id. When the `idAttribute` has been set, Backbone standardizes handling of ids so that `model.id` is always available, even if the id property is called something else. The original id property is available in the Model's `attributes` hash, and as such via the `get` methd. So:

```
model.id === model.get('_id') // -> true

```
You can use the `cid` (client-side ID) attribute of the model as an argument to `MyCollection.get()`, which is guaranteed to exist from creation on. The documentation seems to think that will work, see <http://backbonejs.org/#Collection-get>.