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How can I check whether a field exists or not in MongoDB?
To check whether a field exists or not in MongoDB, you can use the $exists operator.
To understand the above concept, let us create a collection with the document. The query to create a collection with a document is as follows −
> db.checkFieldExistsOrNotDemo.insertOne({"StudentName":"Larry"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92ba4136de59bd9de063a1")
}
> db.checkFieldExistsOrNotDemo.insertOne({"StudentName":"John","StudentAge":21});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92ba4e36de59bd9de063a2")
}
> db.checkFieldExistsOrNotDemo.insertOne({"StudentName":"Chris","StudentAge":24,"StudentCountryName":"US"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92ba6536de59bd9de063a3")
}
> db.checkFieldExistsOrNotDemo.insertOne({"StudentName":"Robert","StudentAge":21,"StudentCountryName":"UK","StudentHobby":["Teaching","Photography"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92ba9d36de59bd9de063a4")
}Display all documents from a collection with the help of find() method. The query is as follows −
> db.checkFieldExistsOrNotDemo.find().pretty();
The following is the output −
{ "_id" : ObjectId("5c92ba4136de59bd9de063a1"), "StudentName" : "Larry" }
{
"_id" : ObjectId("5c92ba4e36de59bd9de063a2"),
"StudentName" : "John",
"StudentAge" : 21
}
{
"_id" : ObjectId("5c92ba6536de59bd9de063a3"),
"StudentName" : "Chris",
"StudentAge" : 24,
"StudentCountryName" : "US"
}
{
"_id" : ObjectId("5c92ba9d36de59bd9de063a4"),
"StudentName" : "Robert",
"StudentAge" : 21,
"StudentCountryName" : "UK",
"StudentHobby" : [
"Teaching",
"Photography"
]
}Here is the query to check whether a field exists or not in MongoDB.
Case 1 − When a field exists.
The query is as follows −
> db.checkFieldExistsOrNotDemo.find({ 'StudentHobby' : { '$exists' : true }}).pretty();The following is the output −
{
"_id" : ObjectId("5c92ba9d36de59bd9de063a4"),
"StudentName" : "Robert",
"StudentAge" : 21,
"StudentCountryName" : "UK",
"StudentHobby" : [
"Teaching",
"Photography"
]
}Case 2 − When a field does not exist.
The query is as follows:
> db.checkFieldExistsOrNotDemo.find({ 'StudentTechnicalSubject' : { '$exists' : true }}).pretty();You will not get anything when a field does not exist.
Updated on: 30-Jul-2019
6K+ Views
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