yes, that was a problem, here response:

{
    "error": false,
    "urls": [
        {
            "id": "3",
            "user_id": "17",
            "user": {
                "id": "17",
                "username": "firstuser"
            }
        },
        {
            "id": "4",
            "user_id": "17",
            "user": {
                "id": "17",
                "username": "firstuser"
            }
        }
    ]
}

@jarektkaczyk now i need implement some custom function to hide user_id ? right?

You can use $hidden property on the model.

But I encourage you to use transformers when you output json, if that's the case.