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MongoDB query to fetch a document that does not have a particular field?
To check for existence, use $exists. Let us create a collection with documents −
> db.demo234.insertOne({"FirstName":"Chris","LastName":"Brown","Age":24});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e418a50f4cebbeaebec5148")
}
> db.demo234.insertOne({"FirstName":"David","LastName":"Miller"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e418a5ff4cebbeaebec5149")
}
> db.demo234.insertOne({"FirstName":"John","LastName":"Smith",Age:34});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e418a70f4cebbeaebec514a")
}Display all documents from a collection with the help of find() method −
> db.demo234.find();
This will produce the following output −
{ "_id" : ObjectId("5e418a50f4cebbeaebec5148"), "FirstName" : "Chris", "LastName" : "Brown", "Age" : 24 }
{ "_id" : ObjectId("5e418a5ff4cebbeaebec5149"), "FirstName" : "David", "LastName" : "Miller" }
{ "_id" : ObjectId("5e418a70f4cebbeaebec514a"), "FirstName" : "John", "LastName" : "Smith", "Age" : 34 }Following is the query to check for existence and fetch document without “Age” field −
> var iterator = db.demo234.find({"Age":{$exists:false}},{"_id":0});
> iterator.forEach(function(d)
...{
... printjson(d);
...})This will produce the following output −
{ "FirstName" : "David", "LastName" : "Miller" }
Updated on: 30-Mar-2020
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