MongoDB - Clearing items in a nested array

Question

If I have a nested array in my schema, how do I tell MongoDB to remove its entries for a specific model?

Schema

var UserSchema = new Schema({
  username: String,
  documents: [Number]
});

I tried something like this:

db.users.update({"username": "tom"}, {"$pullAll": {"documents": []}})

But the items in the nested array are still there.

Answer 1

Your code is not working, because $pullAll requires list of items which should be removed from array. You are passing empty array, thus nothing is removed.

You can simply set documents to empty array instead of removing all items:

db.users.update({"username": "tom"}, {"$set": {"documents": []}})

If you want to avoid creating documents array if "tom" do not have it, then check if array exists when selecting document to update:

db.users.update({username: "tom", documents: {$exists: true}}, 
                {$set: {documents: []}})

UPDATE: Another option to remove all array items is to use $pull with query which satisfies all documents:

db.users.update({username: "tom"}, {$pull: {documents: {$exists: true}}})