$unset (original) (raw)

Note

Disambiguation

The following page refers to the update operator $unset. For the aggregation stage, see $unset.

$unset

The $unset operator deletes a particular field.

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

Consider the following syntax:


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

The specified value in the $unset expression (i.e. "") does not impact the operation.

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

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 (i.e. no operation).

When used with $ to match an array element, $unsetreplaces 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 $unsetwith 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).

Create the products collection:


db.products.insertMany( [

   { "item": "chisel", "sku": "C001", "quantity": 4, "instock": true },

   { "item": "hammer", "sku": "unknown", "quantity": 3, "instock": true },

   { "item": "nails", "sku": "unknown", "quantity": 100, "instock": true }

] )

Update the first document in the products collection where the value of sku is unknown:


db.products.updateOne(

   { sku: "unknown" },

   { $unset: { quantity: "", instock: "" } }

)

updateOne() uses the $unset operator to:

remove the quantity field
remove the instock field


{

  item: 'chisel',

  sku: 'C001',

  quantity: 4,

  instock: true

},

{

  item: 'hammer',

  sku: 'unknown'

},

{

  item: 'nails',

  sku: 'unknown',

  quantity: 100,

  instock: true

}