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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 }
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