I am using the following aggregation query:

```
db.posts.aggregate([
    {
        $lookup: {
            from: "profiles",        
            localField: "user",
            foreignField: "user",
            as: "userDetails"
        }
    }
])

```

It returns a result that looks like this:

```
{
    "_id" : ObjectId("5d1523b98d9dd16d832a8c5e"),
    "user" : ObjectId("5d1504e29dc0bd55461adca7"),
    "recipeName" : "Pizza",
    "ingredients" : "Flour and sauce",
    "userDetails" : [ 
        {
            "_id" : ObjectId("5d1505089dc0bd55461adca8"),
            "user" : ObjectId("5d1504e29dc0bd55461adca7"),
            "handle" : "jack",
            "status" : "Developer"
        }
    ]
}

```

This includes the entire "profile" as a key called "userDetails".
However, I don't want all that information. I only need the user's handle.
I want the result to look *exactly* like this:

```
{
    "_id" : ObjectId("5d1523b98d9dd16d832a8c5e"),
    "user" : ObjectId("5d1504e29dc0bd55461adca7"),
    "recipeName" : "Pizza",
    "ingredients" : "Flour and sauce",
    "handle" : "jack"
}

```

How can I accomplish that?