使用C＃驱动程序从mongodb的数据检索 [英] Retrieve data from mongodb using C# driver

问题描述

我使用C＃MongoDB的官方驱动程序在我的测试项目，我已经插入从C＃Web应用程序MongoDB的文档。在蒙戈控制台，db.blog.find（）可以显示我已经插入条目。但是，当我试图找回它们，.NET抛出一个异常

I'm using official mongodb driver for c# in my test project and i've already insert document from c# web application to mongodb. In mongo console, db.blog.find() can display entries I've inserted. but when i tried to retrieve them, .net throw a exception

System.InvalidOperationException：当CurrentBsonType是字符串，而不是当CurrentBsonType是ReadString只能叫的ObjectId。

我的实体类是非常简单的。

my entity class is very simple

namespace MongoDBTest
{
    public class Blog
    {
        public String _id
        {
            get;
            set;
        }

        public String Title
        {
            get;
            set;
        }
    }
}

这是我的检索码

and this is my retrieve code

public List<Blog> List()
{
    MongoCollection collection = md.GetCollection<Blog>("blog");
    MongoCursor<Blog> cursor = collection.FindAllAs<Blog>();
    cursor.SetLimit(5);
    return cursor.ToList();
}

任何人可以帮助我吗？谢谢！

can anybody help me out? thanks!

推荐答案

我想你只需要标记你的博客标识与 BsonId （插入ID自己）属性：

I suppose you just need mark your blog Id with BsonId (and insert id yourself) attribute:

public class Blog
{
    [BsonId]
    public String Id {get;set;}

    public String Title{get;set;}
}

和所有应该没问题。问题是，因为你没有标明哪一个领域将是MongoDB的_id和驱动程序生成_id字段类型的ObjectId。 ，而当司机试图反序列化回来，他不能转换的ObjectId为String

And all should be okay. Issue was because you not marked what field will be Mongodb _id and driver generated _id field with type ObjectId. And when driver trying deserialize it back he can't convert ObjectId to String.

完整的例子：

MongoCollection collection = md.GetCollection<Blog>("blog");
var blog = new Blog(){Id = ObjectId.GenerateNewId().ToString(), 
                      Title = "First Blog"};
collection .Insert(blog);

MongoCursor<Blog> cursor = collection.FindAllAs<Blog>();
cursor.SetLimit(5);

var list = cursor.ToList();

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