In MongoDB, you can use the $unset field update operator to completely remove a field from a document.

The $unset operator is designed specifically to delete a field and its value from the document.

Example

Suppose we have a collection called dogs with the following documents:

{ "_id" : 1, "name" : "Wag", "type" : "Dog", "weight" : 20 }
{ "_id" : 2, "name" : "Bark", "type" : "Dog", "weight" : 10 }
{ "_id" : 6, "name" : "Fetch", "type" : "Dog", "weight" : 17 }
{ "_id" : 7, "name" : "Jake", "type" : "Dog", "weight" : 30 }

And suppose we want to remove the type field (and its respective value) from all documents.

We can do this:

db.dogs.updateMany(
   { },
   { $unset: { type: "" } }
)

Output:

{ "acknowledged" : true, "matchedCount" : 4, "modifiedCount" : 4 }

This tells us that four documents matched (because we used an empty query document as the first argument) and four were updated.

Now let’s check the collection again:

db.dogs.find()

Result:

{ "_id" : 1, "name" : "Wag", "weight" : 20 }
{ "_id" : 2, "name" : "Bark", "weight" : 10 }
{ "_id" : 6, "name" : "Fetch", "weight" : 17 }
{ "_id" : 7, "name" : "Jake", "weight" : 30 }

We can see that the type field has been completely removed from each document.

Note that the specified value in the $unset expression (i.e. “”) does not impact the operation.

Remove Multiple Fields

You can specify multiple fields to remove by separating them with a comma.

Example:

db.dogs.updateMany(
   { },
   { $unset: { name: "", weight: "" } }
)

Output:

{ "acknowledged" : true, "matchedCount" : 4, "modifiedCount" : 4 }

Check the collection:

db.dogs.find()

Result:

{ "_id" : 1 }
{ "_id" : 2 }
{ "_id" : 6 }
{ "_id" : 7 }

Now only the _id fields are left.

Embedded Documents

You can use dot notation to remove fields from embedded documents.

Suppose we have a collection called pets with the following document:

{
	"_id" : 1,
	"name" : "Wag",
	"details" : {
		"type" : "Dog",
		"weight" : 20,
		"awards" : {
			"Florida Dog Awards" : "Top Dog",
			"New York Marathon" : "Fastest Dog",
			"Sumo 2020" : "Biggest Dog"
		}
	}
}

And suppose we want to remove the awards field from the document.

We can do this:

db.pets.updateMany(
   { _id: 1 },
   { $unset: { "details.awards": "" } }
)

Output:

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }

Now let’s check the document:

db.pets.findOne()

Result:

{
	"_id" : 1,
	"name" : "Wag",
	"details" : {
		"type" : "Dog",
		"weight" : 20
	}
}

The awards field and its value (which was itself an embedded document) has been removed from the document.