How to update document with nested array in mongodb

Question

I've got a document in a collection 'events' with the following structure:

{ 
  "_id" : "abc",
  "text" : "some text",
}

I wish to update the document by inserting an array named guestOwner. The result I want would update the document like this:

{ 
  "_id" : "abc",
  "text" : "some text",
  "guestOwner" : [
    {
        "name" : "JACK BLACK", 
        "guests" : [
            "GUEST1",
            "GUEST2"
        ]
    }
  ]
}

So I tried an mongo update with the following:

db.events.update({ _id: eventid }, { $push: { guestOwner: { name: username, guests: allGuests } } });

where 'username' is a string, and 'allGuests' is an array of names ["Guest1", "Guest2"]

The issue for me is when a subsequent update to the document occurs, I would want to push a the new 'allGuests' array into the existing one if the name is the same. For example, if a second update occurs with 'allGuests' = ["GUEST3"], and with the same name = "JACK BLACK", I would want the document to be:

{ 
  "_id" : "abc",
  "text" : "some text",
  "guestOwner" : [
    {
        "name" : "JACK BLACK", 
        "guests" : [
            "GUEST1",
            "GUEST2"
            "GUEST3"
        ]
    }
  ]
}

BUT, if the document were updated with a different name = 'JOHN SMITH' where allGuests array = ["GUEST3"], it would create:

{ 
  "_id" : "abc",
  "text" : "some text",
  "guestOwner" : [
    {
        "name" : "JACK BLACK", 
        "guests" : [
            "GUEST1",
            "GUEST2"
        ]
    },
    {
        "name" : "JOHN SMITH", 
        "guests" : [
            "GUEST3"
        ]
    }
  ]
}

Would I need conditional statements surrounding the mongo update to check for guestOwner[0].name? Not sure if mongo could do this on its own, or if a bunch of logic is going to be necessary.

score 2 · Accepted Answer · answered Nov 18 '18 at 07:33

You could simply do an update where in the query section you would specify the name:

db.events.update({
  "_id" : ObjectId("someId"), "guestOwner.name": "JACK BLACK"}, {
  $push: { "guestOwner.$.guests": "GUEST11" // etc }
})

If this returns the number of updated elements to be 1 you are good to go since the name exists etc.

If it returns 0 then that name does not exists so you can run:

db.events.update({"_id" : ObjectId("someId")}, {
  $addToSet: { guestOwner: { name: "JACK BLACK" // etc }}
})

It would save you one call since if you have to check if the record exists you would always do 2 rounds. One to check and another to take action based on the result. Here if the records is already there you only do one update.

Ah, yes. Makes perfect sense. – flimflam57 Nov 18 '18 at 13:59 — flimflam57, Nov 18 '18 at 13:59

How to update document with nested array in mongodb

1 Answers1