Can someone please explain isValid in the final $project stage… I don’t ever remember hearing anything about this field. Upon looking at it, I believe it to be a new field name in the project stage, but the $in operator is new to me. Is this essentially an $and statement? It appears to be comparing two arrays to each other. Am I correct in this?
You are right, it is
And as for
They really cannot cover all operators in this somewhat introduction course. It is really important to get acquainted with the documentation.
See the documentation for $in at