MongoDB 和 C# Find()

Question

我有以下代码，而且我是 mongodb 的新手，我需要帮助来查找集合中的特定元素。

using MongoDB.Bson;
using MongoDB.Driver;
namespace mongo_console    {

public class User    {
    public ObjectId Id { get; set; }
    public string name { get; set; }
    public string pwd { get; set; }
}
class Program    {
    static void Main(string[] args)
    {
        MongoClient client = new MongoClient();
        MongoServer server = client.GetServer();
        MongoDatabase db = server.GetDatabase("Users");
        MongoCollection<User> collection = db.GetCollection<User>("users");

        User user = new User
        {
            Id = ObjectId.GenerateNewId(),
            name = "admin",
            pwd = "admin"
        };
        User user2 = new User
        {
            Id = ObjectId.GenerateNewId(),
            name = "system",
            pwd = "system"
        };
        collection.Save(user);
        collection.Save(user2);

        /*
         * How do I collection.Find() for example using the name
         */
  }
}
}

一旦我找到想要打印的用户，这是否可行或只会返回该位置？如果是这样，我该如何打印？

我看过一些示例 collection.Find(x => x.something) 但我不知道 x 是什么意思

Answer 1

要查找记录，您可以在 find 中使用 Lambda，例如：

var results = collection.Find(x => x.name == "system").ToList();

或者，您可以使用与强类型 Lambda 或文本一起使用的构建器：

var filter = Builders<User>.Filter.Eq(x => x.name, "system")

或者

var filter = Builders<User>.Filter.Eq("name", "system")

然后像上面那样使用find

// results will be a collection of your documents matching your filter criteria

// Sync syntax
var results = collection.Find(filter).ToList();

// Async syntax
var results = await collection.Find(filter).ToListAsync();

Answer 2

using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Driver;
using MongoDB.Driver.Builders;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Mongo_console
{
    class Program
    {
        public static void Main(string[] args)
        {
            MongoClient client = new MongoClient();
            MongoServer server = client.GetServer();
            MongoDatabase db = server.GetDatabase("admin");
            MongoCollection<Book> collection = db.GetCollection<Book>("Book");


            Book book1 = new Book
            {
                Id = ObjectId.GenerateNewId(),
                name = "Reel To Real"
            };
            Book book2 = new Book
            {
                Id = ObjectId.GenerateNewId(),
                name = "Life"
            };
            collection.Save(book1);
            collection.Save(book2);

            var query = Query<Book>.EQ(u => u.Id, new ObjectId("5a5ee6360222da8ad498f3ff"));
            Book list = collection.FindOne(query);
            Console.WriteLine( "Book Name  " + list.name);


            Console.ReadLine();
        }
    }
    public class Book
    {
        [BsonId]
        public ObjectId Id { get; set; }
        public string name { get; set; }

        public Book()
        {
        }

        public Book(ObjectId id, string name)
        {
            this.Id = id;
            this.name = name;
        }
    }
}

Answer 3

它也因我们使用的 .Net 框架版本而异。如果我们使用 2x 驱动程序，它应该看起来像：

var list = await collection.Find(new BsonDocument()).ToListAsync();

方法二

await collection.Find(new BsonDocument()).ForEachAsync(X=>Console.WriteLine(X));

Reference Example