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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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.