gistfile1.txt

{"rp":
  {"AdSpot": [
    {"1": {"a": "b"}},
    {"2": {"a": "b"}},
    {"3": {"a": "b"}}]
  }
}

db.collection.find({"rp.AdSpot": {$in: [{"1": {"a": "b"}}, {"2": {"a": "b"}]}})

# Or

{"rp":
  {"AdSpot": [
    {"a": "a"},
    {"a": "b"},
    {"a": "c"}]
  }
}

db.collection.find("rp.AdSpot": {"$in": [{"a": "a"}, {"a": "c"}]})

db.collection.find({"rp.AdSpot.a": "b"})