如何让Mongo LINQ查询只从文档返回子对象？

using MongoDB.Driver;
using MongoDB.Driver.Linq;

// 定义数据模型
public class MyDocument
{
    public ObjectId Id { get; set; }
    public string Name { get; set; }
    public MySubObject SubObject { get; set; }
}

public class MySubObject
{
    public int SubField1 { get; set; }
    public string SubField2 { get; set; }
}

// 创建MongoDB客户端
var client = new MongoClient("mongodb://localhost:27017");
var database = client.GetDatabase("mydb");
var collection = database.GetCollection<MyDocument>("mycollection");

// 使用Mongo LINQ查询
var query = from doc in collection.AsQueryable()
            select new MySubObject
            {
                SubField1 = doc.SubObject.SubField1,
                SubField2 = doc.SubObject.SubField2
            };

// 获取查询结果
var result = query.ToList();