[{"name":"n1","posts":[{"title":"t1","posted_on":1},{"title":"t2","posted_on":2},{"title":"t3","posted_on":3},{"title":"t4","posted_on":4},{"title":"t5","posted_on":5}]}]

db.collection.aggregate([{"$match":{"name":{"$eq":"n1"}}},{"$unwind":{"path":"$posts"}},{"$replaceRoot":{"newRoot":"$posts"}},{"$match":{"$and":[{"posted_on":{"$gt":1}},{"posted_on":{"$lt":5}}]}},{"$limit":2}])