Question

发生System.NullReferenceException HResult = 0x80004003
Message =对象引用未设置为对象的实例 Source = StackTrace：at mongotest.Program.Main（String [] args）in C：\ Users \用户kiit \源\回购\ C＃-code \ mongotest \ mongotest \ Program.cs中：线 20

请帮我解决这个错误。为什么我得到空引用。除此之外，请告诉我如何在MongoDB中获取此架构的数据

{ 

        "_id" : ObjectId("5a78a7365a98c0a0d9118c1a"), 
        "name" : "Amit", 
        "contacts" : [
            "userid1", 
            "userid2"
        ], 
        "logs" : {
            "status" : "online", 
            "Available" : "False"
        }
    }

代码：如何设置日志和联系人的值，我想在数据库中插入这些值。我将对此解决方案做些什么：我将在asp.net中的click事件的数据库中插入值，并从用户获取值。

 using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using MongoDB.Bson;
    using MongoDB.Driver;
    namespace mongotest
    {
        class Program
        {
            static void Main(string[] args)
            {
                /* Connection in MongoDb and insert data in database */
                var client = new MongoClient("mongodb://localhost");
                var database = client.GetDatabase("SIH");
                var collection = database.GetCollection<testing>("testing");
                testing newobject = new testing();
                newobject.name = "Amit Mishra";
                newobject.logs.Available = "true";
                newobject.logs.status = "false";
                collection.InsertOneAsync(newobject);
                Console.Write("Done");
                Console.Read();
            }
        }
    }

    public class testing
    {
        public string _id { get; set; }
        public string name { get; set; }
        public string[] contacts { get; set; }
        public Logs logs { get; set; }
    }

    public class Logs
    {
        public string status { get; set; }
        public string Available { get; set; }
    }

Answer 1

您正在访问未初始化的属性，这就是您获取NullPointerException的原因。

将代码改为：

[...]
newobject.logs = new Logs();
newobject.logs.Available = "true";
[...]

Answer 2

如dnickless所示，您必须初始化日志，并且还必须初始化字符串数组。在您的情况下，代码应该增强到类似：

[...]
newobject.logs = new Logs();
newobject.logs.Available = "true";
newobject.contacts = new string[]{ "userid1", "userid2" };
[...]

如何在mongodb数组中设置值

2 个答案: