Database
[{"_id":ObjectId("640b0e3629cb7001946137a3"),"field1":{"attr1":"","attr2":"","attr3":"","attr4":"","attr5":""},"field2":{"val":"some_val"}},{"_id":ObjectId("640b0e3629cb7001946137a4"),"field1":{"attr1":"","attr2":""},"field2":{"val":"some_val"}}]
Query
db.collection.update({},[{"$set":{"temp_f1":{"$objectToArray":"$field1"}}},{"$set":{"field2.val":{"$cond":[{$setIsSubset:[["attr1","attr2","attr3"],"$temp_f1.k"]},"UPDATED!",""]}}},{"$unset":"temp_f1"}],{multi:true})