使用C#只获取MongoDB中的指定字段

using MongoDB.Bson;
using MongoDB.Driver;

public class Program
{
    public static void Main(string[] args)
    {
        var client = new MongoClient("mongodb://localhost:27017");
        var db = client.GetDatabase("test");
        var collection = db.GetCollection<BsonDocument>("test");

        var filter = Builders<BsonDocument>.Filter.Eq("name", "John");
        var projection = Builders<BsonDocument>.Projection.Include("age").Exclude("_id");

        var result = collection.Find(filter).Project(projection).FirstOrDefault();

        Console.WriteLine(result["age"]);
    }
}