Question

Assuming I have a collection in MongoDB with 5000 records, each containing something similar to:

{
"occupation":"Doctor",
"name": {
   "first":"Jimmy",
   "additional":"Smith"
}

Is there an easy way to rename the field “additional” to “last” in all documents? I saw the $rename operator in the documentation but I’m not really clear on how to specify a subfield.

Answer 1

You can use:

db.foo.update({}, {
    $rename: {
        "name.additional": "name.last"
    }
}, false, true);

Or to just update the docs which contain the property:

db.foo.update({
    "name.additional": {
        $exists: true
    }
}, {
    $rename: {
        "name.additional": "name.last"
    }
}, false, true);

The false, true in the method above are: { upsert:false, multi:true }. You need the multi:true to update all your records.

Or you can use the former way:

remap = function (x) {
    if (x.additional) {
        db.foo.update({
            _id: x._id
        }, {
            $set: {
                "name.last": x.name.additional
            }, $unset: {
                "name.additional": 1
            }
        });
    }
}
    
db.foo.find().forEach(remap);

In MongoDB 3.2 you can also use

db.students.updateMany({}, { 
    $rename: { 
        "oldname": "newname" 
    } 
})

The general syntax of this is

db.collection.updateMany(filter, update, options)

https://docs.mongodb.com/manual/reference/method/db.collection.updateMany/