To search for a field, use $exists and to delete it, use $unset. The $unset operator in MongoDB deletes a particular field.
Let us create a collection with documents −
> db.demo562.insertOne({"Name":"Chris","Age":21});{ "acknowledged" : true, "insertedId" : ObjectId("5e8f4ae854b4472ed3e8e872") } > db.demo562.insertOne({"Age":20});{ "acknowledged" : true, "insertedId" : ObjectId("5e8f4ae954b4472ed3e8e873") } > db.demo562.insertOne({"Name":"David","Age":23});{ "acknowledged" : true, "insertedId" : ObjectId("5e8f4aea54b4472ed3e8e874") }
Display all documents from a collection with the help of find() method −
> db.demo562.find();
This will produce the following output −
{ "_id" : ObjectId("5e8f4ae854b4472ed3e8e872"), "Name" : "Chris", "Age" : 21 } { "_id" : ObjectId("5e8f4ae954b4472ed3e8e873"), "Age" : 20 } { "_id" : ObjectId("5e8f4aea54b4472ed3e8e874"), "Name" : "David", "Age" : 23 }
Following is the query to search for a record and then delete it −
> db.demo562.update( {Name:{$exists:true} },{ $unset: {"Name":""}},{multi:true}); WriteResult({ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 })
Display all documents from a collection with the help of find() method −
> db.demo562.find();
This will produce the following output −
{ "_id" : ObjectId("5e8f4b6654b4472ed3e8e875"), "Age" : 21 } { "_id" : ObjectId("5e8f4b6754b4472ed3e8e876"), "Age" : 20 } { "_id" : ObjectId("5e8f4b6854b4472ed3e8e877"), "Age" : 23 }