MongoDB C# driver: how to use $in operator for nested embedded documents?

Question

I am trying to use the $in operator using the MongoDB C# driver.

Here's an example document:

ObjectField:
    {
      "_id" : ObjectId("59421cd7f39cc1227cb7be55"),
      "ObjectName" : "Customer",
      "FieldName" : "Kind Customer",
      "KeyValues" : [{
          "Key" : "k11",
          "Value" : "v11"
        }, {
          "Key" : "k21",
          "Value" : "v21"
        }]
    }

And here's the first approach I tried:

var database = MongoDbClient.GetDatabase("Database");
var builder = Builders<ObjectField>.Filter;
var keys = new List<string>() { "k11", "k21" };
var filter = builder.Eq("ObjectName", "Customer") & builder.Eq("FieldName", "Kind Customer") & builder.In("KeyValues.Key", keys);
var projection = Builders<ObjectField>.Projection.Include("KeyValues.$");
var bsonDocuments = database.GetCollection<ObjectField>("ObjectField").Find(filter).Project(projection).ToList();

However, it returns only top one KeyValue from the list.

{
        "_id": ObjectId("59421cd7f39cc1227cb7be55"),
        "KeyValues": [{
            "Key": "k11",
            "Value": "v11"
        }]
    }

Here's the 2nd approach I tried:

 var keys = new List<string>() { "k11", "k20" };
 var result = (from x in database.GetCollection<ObjectField>("ObjectField").AsQueryable()
                              where x.KeyValues.Any(y => keys.Contains(y.Key))
                              && x.ObjectName == "Customer" && x.FieldName == "Kind Customer"
                              select x).ToList();

In this case, it returned all nested records which are not included in keys.

Answer 1

var filter = Builders<XXXX>.Filter.In("_id", xxxx.Select(i => i.Id));
mongoClient.GetCollection<XXXX>("XXXX").DeleteMany(filter);