【Question】

Is there a way to use the $map operator in a regular Mongo document query (or aggregate \$match which I believe is the same thing).

What I’m trying to do is this: given a set of sets, return the document if any of the sets is a subset of a parameter.

Example:

Let’s say I have three documents:

{x : [ [“A”,“B”] ] }

{x : [ [“A”, “D”] ] }

{x : [ [“A”,“B”], [“A”,“D”] ] }

And I have an array

auths = [“A”,“B”,“C”]

I want to run a query where I get back the first and third documents because both contain the set [“A”,“B”] which is a subset of auths, but not the second document because its only set contains D which is not in the set of auths.

If I were doing this in a $redact pipeline I could do this with something along the lines of:

{“$anyElementTrue” : {

“$map” : {

“input”: “$x”,

“as”: “s”,

“in”: {“$setIsSubset”: [“$$s”, auths] }

}

}}

But when I try to run this as a query I get

BadValue unknown top level operator: $anyElementTrue

【Answer】

I believe MongoDB API is able to do this though it takes a roundabout route. A more direct way is available if you need. That is Structured Process Language (SPL). The code is as below:

A2:

A3: Define a sequence parameter according to which the user privilege sets are matched.

A4: Match each of A2’s records to see if au contains a set which is the subset of A3’s set, and get it if the result is true.