MongoDB and C# Find()

问题

I have the below code and I am new to mongodb, I need help in finding an specific element in the collection.

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
         */
  }
}
}

Once I find the user I will like to print it, is that posible or will find only return the position? if so, how do I print it?

I have seen some examples collection.Find(x => x.something) but I do not know what that x is or mean

回答1:

To find a record you could use Lambda in find, for example:

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

Alternatively you can use Builders which work with strongly typed Lambda or text:

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

Or

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

And then use find as above

// 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();

回答2:

It also Varies according to the .Net framework version we are using. If we Use 2x driver it should look like :

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

method 2

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

Reference Example

回答3:

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;
        }
    }
}

来源：https://stackoverflow.com/questions/40164908/mongodb-and-c-sharp-find