How to match by 'undefined' value in MongoDB Aggregation Framework?

Question

How can I search for the records filtering in a field that has an undefined value:

db.records.aggregate({
    $match: {
               


        

Answer 1

If you have fields that exist but are undefined you can search for them with null.

db.records.aggregate({
    $match: {
        myField: {$exists: true, $eq: null},
    }
})