MongoDB: SELECT const ?

Question

MongoDB

Does MongoDB have the ability to create queries similar to the SQL variant:
SELECT 1 as num, username FROM 'users' LIMIT 1?
(Task: it is necessary to set some value in the request in order to get it as a result)

Answer 1

In 2.2 it will be possible to use $project. Now I don't know how. Can you clarify the issue? Why get the same field as the input.

Answer 2

Apparently, temporary stubs are required during the development / development of the project, or connection to an existing database, the structure of which differs from the required one.
A universal solution - make a view in the database, in which add the necessary fields.