$unset (update operator)

Definition

$unset

The $unset operator deletes a particular field.

Compatibility

You can use $unset for deployments hosted in the following environments:

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB

• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB

Syntax

Consider the following syntax:

{ $unset: { <field1>: "", ... } }

The specified value in the $unset expression (that is, "") does not impact the operation.

To specify a <field> in an embedded document or in an array, use dot notation.

Behavior

Starting in MongoDB 5.0, update operators process document fields with string-based names in lexicographic order. Fields with numeric names are processed in numeric order. See Update Operators Behavior for details.

If the field does not exist, then $unset does nothing (that is, no operation).

When used with $ to match an array element, $unset replaces the matching element with null rather than removing the matching element from the array. This behavior keeps consistent the array size and element positions.

Starting in MongoDB 5.0, mongod no longer raises an error when you use an update operator like $unset with an empty operand expression ( { } ). An empty update results in no changes and no oplog entry is created (meaning that the operation is a no-op).

Example

The examples on this page use data from the sample_mflix sample dataset. For details on how to load this dataset into your self-managed MongoDB deployment, see Load the sample dataset. If you made any modifications to the sample databases, you may need to drop and recreate the databases to run the examples on this page.

The following example uses the $unset operator to remove the label and status fields from the matching movie document:

db.movies.updateOne(
   { title: "The Dark Knight" },
   { $unset: { label: "", status: "" } }
)

The operation returns the following result:

{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}