我的SQL访问代码中的错误 [英] A bug in my SQL access code

问题描述

我正在编写将sql数据库与前端应用程序连接的代码(.net框架中的设计)
代码如下-----

I was writing the codes to connect sql database with frontend application(design in .net framework)
the codes were as follows-----

private void comboBox1_TextChanged(object sender, EventArgs e)
{
    SqlCommand comm = new SqlCommand("Select log_name from dbo.niraj_table where log_id=''"+Convert.ToInt32(comboBox1.Text)+"''", conn);
    SqlDataReader dr = comm.ExecuteReader();
    textBox1.Text =Convert.ToString( dr["log_name"]);//This line gives me error_____conn is sqlconnection object here
}

代码调试器中显示的错误消息如下:
当没有数据存在时无法读取..

The error message shown in code debugger is as follows:
Unable to read when no data is present..

推荐答案

我猜这是因为您尚未调用SqlDataReader的Read()方法而导致的错误SqlDataReader到下一条记录.

添加以下代码行:

I guess the error is because you haven''t called the SqlDataReader''s Read() method which advances the SqlDataReader to the next record.

Add these lines of code:

if (dr.HasRows)
{
    dr.Read();
    textBox1.Text =Convert.ToString( dr["log_name"]);
    dr.Close();
}

此外，在此行中:

Also, in this line:

SqlCommand comm = new SqlCommand("Select log_name from dbo.niraj_table where log_id='"+Convert.ToInt32(comboBox1.Text)+"'", conn);

您正在将log_id转换为整数，但通过将其用单引号("...")
来作为字符串字段传递 检查数据库中log_id的数据类型.如果是整数，请删除单引号.

希望这对您有帮助！

You are converting the log_id to integer but passing it as a string field by enclosing it in single quotes (''...'')
Check the datatype of log_id in the database. If it''s integer, remove the single quotes.

Hope this helps!

正确检查您的代码我认为您需要查看SqlCommand并将它的第一个参数作为字符串，但这是问题所在

Check your code properly i think you need to see the SqlCommand and it takes 1st argument as string but here is the problem

SqlCommand comm = new SqlCommand("Select log_name from dbo.niraj_table where log_id='"+Convert.ToInt32(comboBox1.Text)+"'", conn);//Error is here 

但是您正在连接不正确的int，并且如果您只想检索一个值，则此解决方案会更好地工作

but you are concatenating int which is not correct and this solution would work better if you want to retrieve only one value

SqlDataReader dr = comm.ExecuteScalar();

然后这个

and then this

if (dr.HasRows)
{
    dr.Read();
    textBox1.Text =Convert.ToString( dr["log_name"]);
    dr.Close();
}

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