Question

我在使用C＃连接数据库时遇到问题。我可以获取并验证我的连接字符串已被检索，但在尝试打开连接后，它无法打开。没有错误消息，只是在打开时返回false。

using System.Data;
using System.Data.SqlClient;

SqlConnection dConnection = new SqlConnection();
public bool isCurrentOpen;

public string ErrorMsg = "";
public int attempt;
public int MaxRetry = 5;

public bool OpenDBConnection(string ConnectionString)
{
    attempt = 0;          
    if(ConnectionString == null)
        ConnectionString = cConn.SetConnectionString();             

        isCurrentOpen = (dConnection.State == ConnectionState.Open);   

        while (!isCurrentOpen && attempt < MaxRetry)                   
        {
            try
            {
                dConnection.Open();                                 
                attempt++;                                          

                if (isCurrentOpen)                                  
                    break;                                         

            }
            catch (Exception ex)
            {
                ErrorMsg += ex.Message;                            
                attempt++;                                         
            }
        }
        return isCurrentOpen;                                      
    }
}

你怎么看？

这是检索连接字符串的位置

public string ConnectionString = "";

            public string GetConnectionString(string ConnectionString)
    {

        if(ConnectionString == "")
        {
             ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings[1].ConnectionString.ToString();
            // Retrieves the Application Settings File and retrieves the Connection String
        }

        return ConnectionString;
    }

     public string SetConnectionString()
     {
         try
        {
            ConnectionString = this.GetConnectionString(ConnectionString);
        }
        catch (Exception ex)
        {
            ErrorMsg += ex.Message;
        }

        return ConnectionString;
    }

更改为不同的数据库并使用SQLCompact数据库并获得相同的结果并再次返回文件中的连接字符串我没有足够的声誉点来将结果截图给你

Answer 1

尝试打开连接后，您不会更新布尔值

isCurrentOpen = (dConnection.State == ConnectionState.Open);   
while (!isCurrentOpen && attempt < MaxRetry)                   
{
    try
    {
        dConnection.Open();                                 
        attempt++;                                          

        // You need to re-evaluate this boolean
        isCurrentOpen = (dConnection.State == ConnectionState.Open);   

        // And, there is no need to break out here, because the loop will terminate 
        // itself if the isCurrentOpen == true
        // if (isCurrentOpen)                                  
        //      break;                                         
    }
    ....
}
return isCurrentOpen;

编辑查看您的编辑，似乎您没有将ConnectionString传递给连接对象。没有它，连接就不知道如何打开数据库

public bool OpenDBConnection(string ConnectionString)
{
    attempt = 0;          
    isCurrentOpen = (dConnection.State == ConnectionState.Open);   
    if(isCurrentOpen == false)
    {
       // If no connectionstring received, get it from the config
       if(ConnectionString == null)
           ConnectionString = cConn.GetConnectionString();    

       // Assign the connectionstring to the connection to be opened
       dConnection.ConnectionString = ConnectionString;
       while (!isCurrentOpen && attempt < MaxRetry)                   
       {
           try
           {
               dConnection.Open();   
               ......

Answer 2

在将连接字符串分配给数据库连接对象时，在代码中找不到。您可以尝试使用开放式连接方法进行分配吗？

要回答第二个问题，请如何在当前库中解决此问题。这就是我建议你做的事情：

public bool OpenDBConnection(string ConnectionString)
{
    attempt = 0;          
    if(ConnectionString == null)
        ConnectionString = cConn.SetConnectionString();             
    isCurrentOpen = (dConnection.State == ConnectionState.Open);   

    if (!isCurrentOpen) //to keep up with your logic in case a connection is already opened.
         dConnection = new SqlConnection(ConnectionString); //Initialize Database connection with the Connection String    
     ...

Answer 3

你可以这样做......

将连接字符串存储在App.Config文件中，并为您的项目制作全局类

以下是App.Config文件的示例代码

<?xml version="1.0" encoding="utf-8" ?>

 <configuration>
 <appSettings>
<add key="ConnString" value="Data Source=.;Initial Catalog=yourdatabase;Integrated Security=True" />
</appSettings>
</configuration>

全球类代码

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;

namespace DAL

{

 public class GlobalClass

{
    public string connectionString;

    public GlobalClass() 
    {
        connectionString = System.Configuration.ConfigurationManager.AppSettings.Get("ConnString");
    }
}}

并且您可以将Global类继承到您的剩余项目类我希望这可以帮助您

这里我们考虑员工类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;

 namespace Employe
 {
   public class Employe : GlobalClass
{
    public Employe()
    {
    }
 //Sample Method 
     public DataTable FillRoleComboBox()
    {
        DataTable dt = new DataTable();
        SqlConnection conn = new SqlConnection(connectionString);
        SqlCommand comm = new SqlCommand("select * from TBLEMPLOYEE", conn);
        SqlDataAdapter SDA = new SqlDataAdapter(comm);
        SDA.SelectCommand = comm;
        SDA.Fill(dt);
        return dt;
    }
}
}

在C＃中打开我的连接到SQL

3 个答案: