CODEWITHSUNDEEP
mongodb
Chris
Chris

Reputation: 397

MongoDB find Documents where all array elements equal some value

Collection:

db.test.find()
{
  { "_id" : ObjectId(...), "arr" : [ "Today", "is", null ] }
  { "_id" : ObjectId(...), "arr" : [ null, null, null ] }
}

I'm trying to find all documents where all of arr equals some value. In this example, I would want the document containing arr : [null, null, null] when given null.

Find documents where ALL elements of an array have a specific value

This solution is close to what I want; however, my array data do not have keys for an $elemMatch to reference. Is there a way to accomplish this query without being unnecessarily costly or restructuring my data?

Thanks!

Upvotes: 3

Views: 4588

Answers (2)

s7vr
s7vr

Reputation: 75914

You can use $elemMatch query operator. It just needs a query.

 db.test.find( { arr:  { $not: { $elemMatch: { $ne: null } } } } )

"$elemMatch" + "$ne"

This part includes all the documents where arr array don't have at least one null value.

These are all the documents which has at least one not null value.

$not

This part will keep the all the documents which are not in "$elemMatch" + "$ne".

These are all the documents that has its all of values as null.

Please accommodate edge cases where field doesn't exist to make sure things work as expected.

Upvotes: 3

helmy
helmy

Reputation: 9497

You can use the the $all operator, but the semantics might not be exactly what you want.

db.test.find({ arr: { $all: [null] } })

That would return both of your test documents.

If you really want to query for an array with 3 null values, you can just query for the literal array:

db.test.find({arr:[null,null,null]})

Upvotes: 0

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