How to search for documents in a collection that are missing a certain field in MongoDB?
If you don't care if the field is missing or null
(or if it's never null
) then you can use the slightly shorter and safer:
db.things.find( { a : null } ); // return if a is missing or null
It's safer because $exists
will return true
even if the field is null, which often is not the desired result and can lead to an NPE.
Yeah, it's possible using $exists:
db.things.find( { a : { $exists : false } } ); // return if a is missing
When is true, $exists matches the documents that contain the field, including documents where the field value is null. If is false, the query returns only the documents that do not contain the field.