Using $pull in Mongodb to remove a deeply embedded object

Question

I'm trying to delete ($pull) an object from an array that's embedded. (Using javascript/node.js driver.)

Here is the sample data, where one, two, three are the levels:

{
    one : "All",
    one : [
        {
        name: "People",
        two: [
            { 
            three_id: 123,
            three: "Jonny",
            },
            { 
            three_id: 456,
            three: "Bobby",
            }
        ]
        },
        {
        name: "Animals",
        two: [
            { 
            three_id: 828,
            three: "Cat",
            },
            { 
            three_id: 282,
            three: "Dog",
            }
        ]
        }
    ]   
}

In this example, I'm trying get rid of "Bobby".

I can successfully match the document at the "three level" if I want, like this:

db.test.find({"one.two.three_id" : 456});

However, I've no idea how to eliminate that record using update. Here are some attempts, none of which work:

// failed attempts
db.test.update({"one.two.three_id" : 456}, {$pull:{'one.$.two.$.three_id': 456}});
db.test.update({"one.two.three_id" : 456}, {$pull:{'three_id': 456}});

// deletes entire level two "People"
db.test.update({"one.two.three_id" : 456}, {$pull: {one: {two : {$elemMatch: {'three_id': 456}}}}});

I read that you cannot use two positional $ operators and that you have to know the index position for the second one. However, I want to avoid having to use the index of the embedded dictionary I want to delete.

reference: Mongodb on pull

http://docs.mongodb.org/manual/reference/operator/update/pull/

Answer 1

The value of the key in your $pull object needs to be the path of the array that you're targeting. This appears to work:

db.test.update(
    {'one.two.three_id': 456},
    {$pull: {'one.$.two': {three_id: 456}}}
);

It looks like the $ represents the index of the first matched array level in this case so it works even though we're matching across multiple nesting levels.