When using findAndModify(), what does the 'upsert' option do?

The 'upsert' option in the findAndModify() function is specifically designed to enhance the operation by adding functionality related to the insertion of documents. When 'upsert' is set to true, if no document matches the criteria specified in the query, the findAndModify() command will create and insert a new document based on the update instructions you have provided. This capability is particularly useful when you want to ensure that there's always a document reflecting the intended state, especially in scenarios where a document may or may not exist.

For instance, if you're trying to update a user's details in a collection and you’re not certain whether that user document is already present, enabling upsert ensures that if the user is not found, a new document with the specified values is created.

This makes it a powerful tool for managing document states without needing to perform separate checks before executing the update command. The other choices refer to actions that do not encapsulate the intended functionality of the upsert option within this context of findAndModify().