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$rename (update operator)

Definition

$rename: The $rename operator updates the name of a field.

Syntax

{ $rename: { <field1>: <newName1>, <field2>: <newName2>, ... } }

The new field name must differ from the existing field name. To specify a <field> in an embedded document, use dot notation.

Consider the following example:

db.students.updateOne(
 { _id: 1 }, { $rename: { 'nickname': 'alias', 'cell': 'mobile' } }
)

The preceding operation renames the nickname field to alias and the cell field to mobile in a document where _id is 1.

Behavior

When you run a $rename operation, MongoDB performs the following actions:

Delete the old <field> and field with <newName> from the document (using $unset).
Perform a $set operation with <newName>, using the value from <field>.

Atomicity

Each document matched by an update command is updated in an individual operation. Update operations (like $rename) only guarantee atomicity on a single-document level.

Field Order

The $rename operation might not preserve the order of the fields in the document.

Update Processing Order

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.

Rename Embedded Document Fields

The $rename operator can move fields into and out of embedded documents.

$rename does not work on embedded documents in arrays.

Other Considerations

If the document already has a field with the <newName>, the $rename operator removes that field and renames the specified <field> to <newName>.
If the field to rename does not exist in a document, $rename does nothing.
Starting in MongoDB 5.0, mongod no longer raises an error when you use an update operator like $rename 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).

Examples

Create the students collection:

db.students.insertMany( [
 {
 "_id": 1,
 "alias": [ "The American Cincinnatus", "The American Fabius" ],
 "mobile": "555-555-5555",
 "nmae": { "first" : "george", "last" : "washington" }
 },
 {
 "_id": 2,
 "alias": [ "My dearest friend" ],
 "mobile": "222-222-2222",
 "nmae": { "first" : "abigail", "last" : "adams" }
 },
 {
 "_id": 3,
 "alias": [ "Amazing grace" ],
 "mobile": "111-111-1111",
 "nmae": { "first" : "grace", "last" : "hopper" }
 }
] )

The documents contain an error, nmae should be name. The examples in the following sections update the documents in the collection.

Rename a Field

To rename a field, call the $rename operator with the current name of the field and the new name:

db.students.updateMany(
 { "nmae": { $ne: null } },
 { $rename: { "nmae": "name" } }
)

This operation checks for documents where the nmae field is not null and updates those documents to rename the nmae field to name:

{
 "_id": 1,
 "alias": [ "The American Cincinnatus", "The American Fabius" ],
 "mobile": "555-555-5555",
 "name": { "first" : "george", "last" : "washington" }
}
{
 "_id" : 2,
 "alias" : [ "My dearest friend" ],
 "mobile" : "222-222-2222",
 "name" : { "first" : "abigail", "last" : "adams" }
}
{
 "_id" : 3,
 "alias" : [ "Amazing grace" ],
 "mobile" : "111-111-1111",
 "name" : { "first" : "grace", "last" : "hopper" }
}

Rename a Field in an Embedded Document

To rename a field in an embedded document, call the $rename operator using the dot notation to refer to the field. If the field is to remain in the same embedded document, also use the dot notation in the new name, as in the following:

db.students.updateOne( { _id: 1 }, { $rename: { "name.first": "name.fname" } } )

This operation renames the embedded field first to fname:

{
 _id: 1,
 alias: [ 'The American Cincinnatus', 'The American Fabius' ],
 mobile: '555-555-5555',
 name: { last: 'washington', fname: 'george' }
}

Rename a Field That Does Not Exist

When renaming a field and the existing field name refers to a field that does not exist, the $rename operator does nothing, as in the following:

db.students.updateOne( { _id: 1 }, { $rename: { 'wife': 'spouse' } } )

This operation does nothing because there is no field named wife.

Tip

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