# How to determine whether a field exists in MongoDB?

You need to use $exists operator to determine whether a field exists in MongoDB. Let us first create a collection with documents > db.determineFieldExistsDemo.insertOne({"ClientName":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb245d628fa4220163b75") } > db.determineFieldExistsDemo.insertOne({"ClientName":"Larry","ClientAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb25cd628fa4220163b76") } > db.determineFieldExistsDemo.insertOne({"ClientName":"Mike","ClientCountryName":"UK"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb26fd628fa4220163b77") } > db.determineFieldExistsDemo.insertOne({"ClientName":"Sam","ClientAge":24}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb286d628fa4220163b78") } Following is the query to display all documents from a collection with the help of find() method > db.determineFieldExistsDemo.find().pretty(); This will produce the following output { "_id" : ObjectId("5c9eb245d628fa4220163b75"), "ClientName" : "John" } { "_id" : ObjectId("5c9eb25cd628fa4220163b76"), "ClientName" : "Larry", "ClientAge" : 23 } { "_id" : ObjectId("5c9eb26fd628fa4220163b77"), "ClientName" : "Mike", "ClientCountryName" : "UK" } { "_id" : ObjectId("5c9eb286d628fa4220163b78"), "ClientName" : "Sam", "ClientAge" : 24 } Following is the query to determine whether a field exists > db.determineFieldExistsDemo.find({ClientCountryName:{$exists:true}}).pretty();

This will produce the following output

{
"_id" : ObjectId("5c9eb26fd628fa4220163b77"),
"ClientName" : "Mike",
"ClientCountryName" : "UK"
}