$rename operator for field names in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $rename operator do in MongoDB?

The $rename operator changes the name of a field in a document without altering its value.

beginner

How do you use $rename to rename a field called oldName to newName?

Use { $rename: { 'oldName': 'newName' } } inside an update operation to rename the field.

intermediate

Can $rename rename multiple fields at once?

Yes, you can rename multiple fields by listing them all inside the $rename object, like { $rename: { 'old1': 'new1', 'old2': 'new2' } }.

intermediate

What happens if the new field name already exists when using $rename?

MongoDB will overwrite the existing field with the renamed field's value.

advanced

Is it possible to rename a nested field using $rename?

Yes, you can rename nested fields by specifying the full path with dot notation, like { $rename: { 'address.street': 'address.road' } }.

Which MongoDB operator is used to rename a field in a document?

A $unset

B $set

C $rename

D $push

The $rename operator changes the name of a field.

How do you rename the field username to user_name in MongoDB?

A { $rename: { 'username': 'user_name' } }

B { $unset: { 'username': '' } }

C { $set: { 'user_name': 'username' } }

D { $rename: { 'user_name': 'username' } }

The syntax is { $rename: { 'oldField': 'newField' } }.

What happens if the new field name already exists when using $rename?

A The operation fails with an error.

B The existing field is overwritten.

C Both fields are kept with the same name.

D The rename is ignored.

MongoDB overwrites the existing field with the renamed field's value.

Can $rename be used to rename nested fields?

A No, it only works on top-level fields.

B Only if the nested field is an array.

C Only if the nested field is a string.

D Yes, by using dot notation for the field path.

You rename nested fields by specifying the full path with dot notation.

Which of the following is a valid $rename update to rename two fields at once?

A { $rename: { 'a': 'b', 'c': 'd' } }

B { $rename: { 'a': 'b' }, { 'c': 'd' } }

C { $rename: ['a', 'b', 'c', 'd'] }

D { $rename: 'a to b, c to d' }

Multiple fields can be renamed by listing them inside the same $rename object.

Explain how to rename a field in a MongoDB document using the $rename operator.

Think about how you tell MongoDB which field to change and what to rename it to.

Describe what happens if the new field name already exists when using $rename.

Consider if MongoDB merges, errors, or replaces fields.