Database
[{_id:ObjectId("5a934e000102030405000000"),subscriberOf:[{town:ObjectId("5a934e000102030405100000")},{town:ObjectId("58252a796f1aaf645c94f00e")},{town:ObjectId("58252a796f1aaf645c94f02d")},{town:ObjectId("58252a796f1aaf645c94f02d")},{town:ObjectId("58252a7d6f1aaf645c94f2cf")},{town:ObjectId("58252a7b6f1aaf645c94f132")},{town:ObjectId("58252a796f1aaf645c94f02f")},{town:ObjectId("58252a796f1aaf645c94f02f")}]}]
Query
db.collection.aggregate([{$unwind:"$subscriberOf"},{$match:{"subscriberOf.town":{$in:[ObjectId("58252a796f1aaf645c94f00e"),ObjectId("58252a796f1aaf645c94f02d"),ObjectId("58252a7d6f1aaf645c94f2cf"),ObjectId("58252a7b6f1aaf645c94f132"),ObjectId("58252a796f1aaf645c94f02f")]}}},{$group:{_id:"$_id",subscriberOf:{$addToSet:"$subscriberOf"}}}])