我创建了一个程序,可以根据输入的邮政编码从数据库中提取相应的州/城市,但如果以世界"未知"的形式输入非有效、不相应的邮政编码,我需要帮助输出"错误"在州/城市标签中。
我尝试了一堆if语句,但无济于事。
private void BtnLookup_Click(object sender, EventArgs e)
{
String cnStr;
SqlConnection cn = new SqlConnection();
cnStr = "Data Source=000.00.000.00;Initial Catalog=. ;User ID=. ;Password=. ";
//Assigns Connection string to the connection object
cn.ConnectionString = cnStr;
//Open the connection to the SQL Server
cn.Open();
//This statement creates the command object and passes in the SQL statement
//then associates the command to the cn connection object
SqlCommand cmd = new SqlCommand("select distinct state, city from tblZipcodes where zip = @ZipCode", cn);
cmd.Parameters.Add(new SqlParameter("@ZipCode", SqlDbType.NVarChar) { Value = txtZip.Text });
SqlDataReader rdrZip = cmd.ExecuteReader();
while (rdrZip.Read())
{
String myString = rdrZip["state"].ToString().Trim();
String myString2 = rdrZip["city"].ToString().Trim();
lblState.Text = myString;
lblCity.Text = myString2;
}
cn.Close();
}
如果输入了无效的 ZIP,则在州/城市标签中输入未知
一种选择是使用 SqlDataReader.HasRows 检查查询是否返回结果
获取一个值,该值指示 SqlDataReader 是否包含一行或多行。
你可以像这样实现它,
if (rdrZip.HasRows)
{
while (rdrZip.Read())
{
String myString = rdrZip["state"].ToString().Trim();
String myString2 = rdrZip["city"].ToString().Trim();
lblState.Text = myString;
lblCity.Text = myString2;
}
}
else
{
lblState.Text = "Unknown";
lblCity.Text = "Unknown";
}