连接字符串不起作用对象实例引用为空 [英] Connection String Is not Working Object instance reference is null

问题描述

//对象引用未设置为对象的实例。
请不要将其标记为多余的问题。
我尝试了几乎所有方法来创建连接字符串

//'Object reference not set to an instance of an object.' Please Do not mark it as redundant question . I have tried almost all the methods to make a connection string

第一个方法是：

string connectionString = ConfigurationManager.ConnectionStrings["ClinicalConnectionString"].ConnectionString;

第二个一个：

   string connectionstringgg = Properties.Settings.Default.ClinicalConnectionString;

第三种方法是：

third method is by :

 ConnectionStringSettings connectionSetting = ConfigurationManager.ConnectionStrings["ClinicalConnectionString"];

//我建立的连接的名称

//the name of the connection i made

SqlConnection连接=新的SqlConnection（connectionString）;

SqlConnection connection = new SqlConnection(connectionString);

在应用程序配置中：

<connectionStrings>
    <add name="ClinicalDAO.Properties.Settings.ClinicalConnectionString"
        connectionString="Data Source=DESKTOP-I07DSQC;Initial Catalog=db_clinics;Integrated Security=True"
        providerName="System.Data.SqlClient" />
</connectionStrings>

在网络配置中

  <connectionStrings>
    <add name="ClinicalDAO.Properties.Settings.ClinicalConnectionString"
        connectionString="Data Source=DESKTOP-I07DSQC;Initial Catalog=db_clinics;Integrated Security=True"
        providerName="System.Data.SqlClient" />
  </connectionStrings>

任何帮助，它仍然会给我同样的错误：/////'未设置对象引用'///

ANY HELP PLEASE it still give me the same error : /////'Object reference not set to an instance of an object.'///

推荐答案

有很多方法可以在C＃中连接到SQL Server数据库。应用程式。

There are many ways to connect to your SQL Server database within a C# app.

1. 不建议使用的第一种方法是硬编码：

1. The First way, that is not recommended, is hard coding:

public void CreateMySqlConnection()
{
    MySqlConnectionStringBuilder myCSB = new MySqlConnectionStringBuilder();
    myCSB.Port = 3307;
    myCSB.Host = "localhost";
    myCSB.UserId = "root";
    myCSB.Password = "mypassword";
    myCSB.Direct = true;
    myCSB.Compress = true;
    myCSB.Database = "demobase";
    myCSB.MaxPoolSize = 150;
    myCSB.ConnectionTimeout = 30;
    MySqlConnection myConnection = new MySqlConnection(myCSB.ConnectionString);
}

来自：

from: https://www.devart.com/dotconnect/connection-strings.html?gclid=CjwKCAjwy_XaBRAWEiwApfjKHt-Yn6Ja43anKj0cvAzDHL5eNDHKvaxwnq5IEsVyHY-rR3GECsa6shoCZH8QAvD_BwE

 <添加名称= MovieDB 
 connectionString = Data Source = LocalDb）\MSSQLLocalDB;初始目录= aspnet-MvcMovie;集成安全性= SSPI; AttachDBFilename = | DataDirectory | \Movies.mdf 
 providerName = System.Data.SqlClient /> 
  

要阅读它：

System.Configuration.Configuration rootWebConfig =
            System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("/MyWebSiteRoot");
        System.Configuration.ConnectionStringSettings connString;
        if (rootWebConfig.ConnectionStrings.ConnectionStrings.Count > 0)
        {
            connString =
                rootWebConfig.ConnectionStrings.ConnectionStrings["MovieDB"];
            if (connString != null)
                Console.WriteLine("MovieDB connection string = \"{0}\"",
                    connString.ConnectionString);
            else
                Console.WriteLine("No MovieDB connection string");
        }

web.config标签 name上的名称

The name at your web.config tag 'name'

    <add name="MovieDB".....

必须与您的C＃代码相同：

has to be the same one from your c# code:

    connString = rootWebConfig.ConnectionStrings.ConnectionStrings["MovieDB"]

您无需像以前一样指定大名： ClinicalDAO.Properties.Settings.ClinicalConnectionString

You don´t need to specify a large name as you did: "ClinicalDAO.Properties.Settings.ClinicalConnectionString"

使其更小，更简单。

来自： https://msdn.microsoft.com/en-us/library/ms178411.aspx

别忘了在web.config中保护连接字符串。
请阅读：
https：// msdn .microsoft.com / en-us / library / ms178372.aspx

Don´t forget to secure your connection string at your web.config. Please, read this: https://msdn.microsoft.com/en-us/library/ms178372.aspx

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