Question

183

Find documents with array that doesn't contains a specific value

rated 0 times [ 187] [ 4] / answers: 1 / hits: 31016 / 10 Years ago, tue, october 21, 2014, 12:00:00

I have the following model:

var PersonSchema = new Schema({

    name: String,

    groups: [

        {type: Schema.Types.ObjectId, ref: 'Group'}

    ],

});

I am looking for a query that retrieves all the Persons that are not part of a certain Group (i.e the persons' group array doesn't contain the id of the specified group).

I was thinking about something like this, but I'm not sure it is correct:

Person.find({groups: {$nin: [group._id]})

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ignacio

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answered 10 Years ago bradleymoisesy · Accepted Answer

Nothing wrong with what you are basically attempting, but perhaps the only clarification here is the common misconception that you need operators like $nin or $in when querying an array.

Also you really need to do here is a basic inequality match with $ne:

Person.find({ groups: { $ne: group._id } })

The array operators are not for array targets but for providing a list of conditions to test in a convenient form.

Person.find({ groups: { $nin: [oneId, twoId,threeId] } })

So just use normal operators for single conditions, and save $in and $nin for where you want to test more than one condition against either a single value or a list. So it's just the other way around.

If you do need to pass a list of arguments where none of those in the provided list match the contents of the array then you reverse the logic with the $not operator and the $all operator:

Person.find({ groups: { $not: { $all: [oneId,twoId,threeId] } } })

So that means that none of the list provided are present in the array.