How to find a document by the non-existence of a field in MongoDB?

To find a document by the non-existence of a field in MongoDB, the syntax is as follows −

db.yourCollectionName.find({ "yourFieldName" : { "$exists" : false } }).pretty();

To understand the above syntax, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.findDocumentNonExistenceFieldDemo.insertOne({"StudentName":"John","StudentAge":25});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8a5c629064dcd4a68b70e8")
}
> db.findDocumentNonExistenceFieldDemo.insertOne({"StudentName":"David","StudentAge":26,"StudentMathMarks":78});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8a5c809064dcd4a68b70e9")
}

Display all documents from a collection with the help of find() method. The query is as follows −

> db.findDocumentNonExistenceFieldDemo.find().pretty();

The following is the output −

{
   "_id" : ObjectId("5c8a5c629064dcd4a68b70e8"),
   "StudentName" : "John",
   "StudentAge" : 25
}
{
   "_id" : ObjectId("5c8a5c809064dcd4a68b70e9"),
   "StudentName" : "David",
   "StudentAge" : 26,
   "StudentMathMarks" : 78
}

Here is the query to find a document by the non-existence of a field −

> db.findDocumentNonExistenceFieldDemo.find({ "StudentMathMarks" : { "$exists" : false } }).pretty();

The following is the output −

{
   "_id" : ObjectId("5c8a5c629064dcd4a68b70e8"),
   "StudentName" : "John",
   "StudentAge" : 25
}