How to generate mongodb object id for a sub-document on insert

Question

Inserting a document that also has sub-documents. I am doing this through cli. How do I make mongodb generate a object id for the Alerts sub-document record? I want something like the following, but this does not work from cli.

db.user.insert(
{
    "Email" : "[email protected]",
    "Domain" : "other",
    "Type" : "local",
    "FName" : "Andy",
    "Alerts" : [ 
        {
            "_id" : new ObjectId(),
            "Keyword" : "sales",
            "Frequency" : {
                "Type" : "daily"
            },
            "IsActive" : true
        }, 
        {
            "_id" : new ObjectId(),
            "Keyword" : "customer service",
            "Frequency" : {
                "Type" : "daily"
            },
            "IsActive" : true
        } 
    ]
}
)

Answer 1

You can run that exact script on the console on robomongo, it would execute just fine. Don't do it on add or edit dialog.