我无法弄清如何更新 MongoDB 集合中的条目。我已经查看了 C# 驱动程序的文档(链接),而且我认为我已经非常密切地遵循了它们。
然而,我传递给 Update 方法的一个(或者也许两个?)参数是无效的。有谁能告诉我我做错了什么?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Driver;
using MongoDB.Driver.Linq;
namespace Csharp_Linq
{
class Program
{
public class Book
{
// Fields
public string title { get; set; }
public string author { get; set; }
public ObjectId id { get; set; }
// Constructors
public Book()
{
this.title = "some title";
this.author = "some author";
}
public Book(string title, string author)
{
this.title = title;
this.author = author;
}
}
static void Main(string[] args)
{
// Connect to the server
string connectionString = "mongodb://localhost";
MongoClient client = new MongoClient(connectionString);
MongoServer server = client.GetServer();
// Get the database then the collection
MongoDatabase database = server.GetDatabase("tutorial");
MongoCollection collection = database.GetCollection("books");
// Query the collection
int count =
(from book in collection.AsQueryable<Book>()
select book)
.Count();
string numBooks = String.Format("This collection has {0} books.", count);
Console.WriteLine(numBooks);
var query =
from book in collection.AsQueryable<Book>()
where book.author == "Ernest Hemingway"
select book;
foreach (var book in query)
{
string bookInfo = String.Format("{0} by {1}", book.title, book.author);
Console.WriteLine(bookInfo);
}
// Insert new books
Book scaryBook = new Book("Dr. Sleep", "Stephen King");
Book[] batch =
{
new Book(),
scaryBook
};
collection.InsertBatch(batch);
// Update default book
var query2 =
from book in collection.AsQueryable<Book>()
where book.title == "some title" && book.author == "some author"
select book;
var update = new UpdateDocument {
{ "$set", new BsonDocument("title", "War and Peace") }
};
BsonDocument updatedBook = collection.Update(query2, update);
Console.ReadLine();
}
}
}
我很惊讶Update方法实际上返回一个BsonDocument。为什么会这样?
之前,我尝试使用如下示例中的Update对象:
MongoCollection<BsonDocument> books;
var query = Query.And(
Query.EQ("author", "Kurt Vonnegut"),
Query.EQ("title", "Cats Craddle")
);
var update = Update.Set("title", "Cat's Cradle");
BsonDocument updatedBook = books.Update(query, update);
这个对象还存在吗?每当我在Visual Studio中打入它时,都会出现一个错误,说该对象不在命名空间中。