Asynchronously removes one entry in a database or adds a new one if it doesn't exist. Usage e.g. for toggling a flag.
Returns a promise resolving to false if the entry was found and removed,
or true if the entry was added. The returned value reflects the state of the database
after the operation.
Asynchronously updates one entry in a database or adds a new one if it doesn't exist.
Add data to a database.