Question

您好我正在尝试将数据库中的数据存储到变量中，然后尝试处理它。但不知何故，变量不会从数据库中读取任何数据并给出其初始值。继承人的代码

int c1=0,c2=0.c3=0,c4=0,sum;

if (rbFour.Checked == true)
        {
            proce = cmb1.Text + "," + cmb2.Text + "," + cmb3.Text + "," + cmb4.Text;
            SqlDataAdapter d = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb1.ValueMember, Program.con);
            DataTable t = new DataTable();
            foreach (DataRow row in t.Rows)
            {

            c1 = Convert.ToInt32(row[0]);
        }
        SqlDataAdapter qd = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb2.ValueMember, Program.con);
        DataTable qt = new DataTable();
        foreach (DataRow row in qt.Rows)
        {

            c2 = Convert.ToInt32(row[0]);
        }
        SqlDataAdapter wd = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb3.ValueMember, Program.con);
        DataTable wt = new DataTable();
        foreach (DataRow row in wt.Rows)
        {

            c3 = Convert.ToInt32(row[0]);
        }
        SqlDataAdapter ed = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb4.ValueMember, Program.con);
        DataTable et = new DataTable();
        foreach (DataRow row in et.Rows)
        {

            c4 = Convert.ToInt32(row[0]);
        }
    }
    else if (rbThree.Checked == true)
    {
        proce = cmb1.Text + "," + cmb2.Text + "," + cmb3.Text;
        SqlDataAdapter d = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb1.ValueMember, Program.con);
        DataTable t = new DataTable();
        foreach (DataRow row in t.Rows)
        {

            c1 = Convert.ToInt32(row[0]);
        }
        SqlDataAdapter qd = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb2.ValueMember, Program.con);
        DataTable qt = new DataTable();
        foreach (DataRow row in qt.Rows)
        {

            c2 = Convert.ToInt32(row[0]);
        }
        SqlDataAdapter wd = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb3.ValueMember, Program.con);
        DataTable wt = new DataTable();
        foreach (DataRow row in wt.Rows)
        {

            c3 = Convert.ToInt32(row[0]);
        }
    }
    else if (rbTwo.Checked == true)
    {
        proce = cmb1.Text + "," + cmb2.Text;
        SqlDataAdapter d = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb1.ValueMember, Program.con);
        DataTable t = new DataTable();

        foreach (DataRow row in t.Rows)
        {

            c1 = Convert.ToInt32(row[0]);
        }
        SqlDataAdapter qd = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb2.ValueMember, Program.con);
        DataTable qt = new DataTable();
        qd.Fill(qt);
        foreach (DataRow row in qt.Rows)
        {

            c2 = Convert.ToInt32(row[0]);
        }

    }
    else
    {
        proce = cmb1.Text;
        SqlDataAdapter d = new SqlDataAdapter("Select Amount from addpro where SSN=" + cmb1.ValueMember, Program.con);
        DataTable t = new DataTable();
        foreach (DataRow row in t.Rows)
        {

            c1 = Convert.ToInt32(row[0]);
        }
    }

任何人都可以帮助这个。几天前我使用相同的代码。工作正常。但现在我不知道它有什么问题。我需要解决方案asap任何人都可以帮助PLZ？

Answer 1

在使用DataTable之前，您需要Fill

  SqlDataAdapter d = new SqlDataAdapter("...", con);
  DataTable t = new DataTable();
  d.Fill(t);  // Here

以及其他适配器等。

但是，让我展示一种不同的方法：

string sqlText = "Select Amount from addpro where SSN=@ssn";
SqlCommand cmd = new SqlCommand(sqlText, Program.con);
cmd.Parameters.AddWithValue("@ssn", cmb1.ValueMember);
object result = cmd.ExecuteScalar();
if(result != null)
    c1 = Convert.ToInt32(result);

您将返回包含单个值的单行（如果找到）。这是SqlCommand的ExecuteScalar方法提供的使用方案。无需创建SqlAdapter，DataTable并使用单行/值填充它。

此外，我已删除了字符串连接并使用了参数化查询来避免Sql注入攻击。尽管如此，在您的代码中有点不太可能，在任何地方都可以使用它。

使用上面的代码，很容易构建一个接收组合框控件的常用方法，应用所需的逻辑并返回整数值

 private int GetComboValue(ComboBox cbo)
 {
      // all the code above replacing cmb1 with cbo and c1 with ssnNumber
      .....
      return ssnNumber;
 }

现在你可以使用

了

if (rbFour.Checked == true)
{
   c1 = GetComboValue(cmb1);
   c2 = GetComboValue(cmb2);
   c3 = GetComboValue(cmb3);
   c4 = GetComboValue(cmb4);
}

Answer 2

使用fill（）方法首先使用dataadapter填充数据表，然后尝试访问数据行

ex：d.fill（dt）;

使用C＃从数据库检索数据到数据

2 个答案: