Mongodb: Find documents with array where at least one element does not match ObjectID

Question

I am struggling with a MongoDB request. I have a Play schema that holds an array of Move objects. Each Move object holds a reference to a Player in the form of an ObjectID. Following this question I tried to do

{ 'moves.player': { $elemMatch : { $ne : playerId } } }

where playerId holds an ObjectID. However I get the error

Error: Can't use $elemMatch with ObjectId

I have also tried the following

{ 'moves.player.str': { $elemMatch : { $ne : playerId.toString() } } }

but it doesn't find the proper documents... Any ideas?

Example

Some Play records:

A = {
    "moves": [
        { player: { $oid: "56f32fe2f41638de3b3e4773" } },
        { player: { $oid: "56f32fe2f41638de3b3e4774" } }
    ]
}
B = {
    "moves": [
        { player: { $oid: "56f32fe2f41638de3b3e4773" } }
    ]
}

Query for playerId = "56f32fe2f41638de3b3e4773" should only return object A, since it is the only one that has an array of moves where at least one of the players is different from 56f32fe2f41638de3b3e4773.

Unfortunately. Even though you found your own solution ( or at least you think you did ) this question does not show the document structure that you are in fact querying. Therefore it is of little use to anyone as an example, and is a very unclear question. Showing a sample document you expect to match would make it better. — Blakes Seven
– Blakes Seven, Commented Mar 24, 2016 at 6:48
Good suggestion, added an example, this might help understanding the problem. Was stuck on this one for a long time, so I suspect it could be useful to someone else. — Barnabé Monnot
– Barnabé Monnot, Commented Mar 24, 2016 at 7:10

Barnabé Monnot · Accepted Answer · 2016-03-24 06:26:48Z

3

OK, found out where the problem was... Just do

{ "moves": { $elemMatch: { "player": { $ne : playerId } } } }

and it works out fine!

answered Mar 24, 2016 at 6:26

Barnabé Monnot

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3 Comments

Blakes Seven Over a year ago

Pretty sure that if your data looks like I "think" it does ( already told you it's not good to ask questions without a sample for others to solve the problem ) then simply { "moves.player": { "$ne": playerId } } is enough. You only need $elemMatch when "two or more" conditions for properties need to be met. Single property inspection can be done with plain "dot notation".

Barnabé Monnot Over a year ago

$ne would not return the Play records where one of the moves was assigned to the player with playerId, so in my example wouldn't return neither A nor B...

Blakes Seven Over a year ago

Ah. Now I get it. Your answer is the right approach.

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