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Find items that do not have a certain field in MongoDB?
To find items that do not have a certain field, use the $exists operator. The syntax is as follows −
> db.yourCollectionName.find({"yourItemName":{$exists:false}}).pretty();
To understand the syntax, let us create a collection with the document. The query to create a collection with a document is as follows −
> db.findDocumentDoNotHaveCertainFields.insertOne({"UserId":101,"UserName":"John","UserAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a95fb6cea1f28b7aa07fb") } > db.findDocumentDoNotHaveCertainFields.insertOne({"UserName":"David","UserAge":22,"UserFavouriteSubject":["C","Java"]}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a96116cea1f28b7aa07fc") } > db.findDocumentDoNotHaveCertainFields.insertOne({"UserName":"Bob","UserAge":24,"UserFavouriteSubject":["MongoDB","MySQL"]}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a96306cea1f28b7aa07fd") }
Display all documents from a collection with the help of find() method. The query is as follows −
> db.findDocumentDoNotHaveCertainFields.find().pretty();
The following is the output −
{ "_id" : ObjectId("5c8a95fb6cea1f28b7aa07fb"), "UserId" : 101, "UserName" : "John", "UserAge" : 21 } { "_id" : ObjectId("5c8a96116cea1f28b7aa07fc"), "UserName" : "David", "UserAge" : 22, "UserFavouriteSubject" : [ "C", "Java" ] } { "_id" : ObjectId("5c8a96306cea1f28b7aa07fd"), "UserName" : "Bob", "UserAge" : 24, "UserFavouriteSubject" : [ "MongoDB", "MySQL" ] }
Here is the query to find items that do not have certain field i.e. UserFavouriteSubject −
> db.findDocumentDoNotHaveCertainFields.find({"UserFavouriteSubject":{$exists:false}}).pretty();
The following is the output −
{ "_id" : ObjectId("5c8a95fb6cea1f28b7aa07fb"), "UserId" : 101, "UserName" : "John", "UserAge" : 21 }
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