want to prune the elements of a nested array which do not satisfy a certain condition:

The structure of my document is:

{"array1":[{"array2":[{"field1":{"field2":"MATCH"}}]}]}The redact query I´m trying to do is: db.getCollection("collection").aggregate([{"$match" : {"array1.array2.field1.field2" : "MATCH",{"$redact" : {"$cond" : {"if" :

{"$in" : ["$array1.array2.field1.field2",["MATCH"]]}

,"then" : "$$KEEP","else" : "$$PRUNE"}}}]);}}

I never can get any result. However if I replace "$array1.array2.field1.field2" with "MATCH" I get a true condition and keeps all the documents. My question is what am I doing wrong for the value of the expression "$array1.array2.field1.field2" never to be equal to "MATCH" if it is the value of field2?

I also need the returned documents in its original structure.

 

I'm using   MongoDB 4.0