C# SQL DataReader:如何只读一次

本文关键字：SQL 一次 只读 何只读 DataReader | 更新日期: 2023-09-27 18:32:03

只有一次，谢谢你的帮助！

Public string panda(string lola = @"Server=.'SQLEXPRESS; DataBase=panda; Integrated Security=true;")
{
      SqlConnection panda = new SqlConnection(lola);
      panda.Open();
      return lola;         
}
public string Show_details(string Command = "Select name From panda")
{
     SqlConnection cn = new SqlConnection(panda());
     SqlCommand Show;
     SqlDataReader read;
     Show = new SqlCommand(Command, cn);
     cn.Open();
     read = Show.ExecuteReader();
     while (read.Read())
     {
        listBox1.Items.Add(read["name"]);
     }
     return Command;
}
private void button3_Click(object sender, EventArgs e)
{
   Show_details();
}

我正在寻找如何让读者读取数据并将其仅发布一次到列表框中！

C# SQL DataReader:如何只读一次

如果我正确理解了你的问题，你只想进入阅读器循环一次。 "虽然"，没有双关语，有更有效的方法可以解决这个问题，你可以声明一个布尔标志，看看你是否已经进入循环。进入循环后，将其更改为 false，以便在下次评估 while 条件时，它将计算为 false 结束循环。见下文。 

public string Show_details(string Command = "Select name From panda")
{
     SqlConnection cn = new SqlConnection(panda());
     SqlCommand Show;
     SqlDataReader read;
     Show = new SqlCommand(Command, cn);
     cn.Open();
     read = Show.ExecuteReader();
     // Declare flag to see if you've hit the reader yet.
     bool hasntYetRead = true;
     // Add a second condition to determine if to cursor through again
     while (read.Read() && hasntYetRead )
     {
        listBox1.Items.Add(read["name"]);
         // Change the flag to false
         hasntYetRead = false;
     }
     return Command;
}

如果您希望将来能够更改次数或迭代次数，则可以使用计数器。

public string Show_details(string Command = "Select name From panda")
{
     SqlConnection cn = new SqlConnection(panda());
     SqlCommand Show;
     SqlDataReader read;
     Show = new SqlCommand(Command, cn);
     cn.Open();
     read = Show.ExecuteReader();
     // declare counter
     int counter = 0;
     // Add a second condition to determine if to cursor through again
     while (read.Read() && counter < 1) //could get counter to count to user input number
     {
         listBox1.Items.Add(read["name"]);
         // Change the flag to false
         counter++;
     }
     return Command;
}
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