Question

我创建了会员维护代码，我将在其中检索会员ID，姓名和所有基本内容 我的代码如下：

private void Mem_Maintenance_Load(object sender, EventArgs e)
{
    try
    {
        txt_mem_id.Text = Generate_no.gen_no("MEM").ToString();
    }
    catch(Exception Ex)
    {
        MessageBox.Show("Error\n\n"+Ex.ToString());
    }
}

我创建了一个名为Library的ClassLibrary，其代码如下

namespace LIBRARY
{ 
public class Generate_no
{
    public static int gen_no(string P_PRM_TYPE)
    {   OleDbConnection connection = new OleDbConnection();
        connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=E:\arekh\MS Access\soc_data.accdb;Persist Security Info=False;";
        connection.Open();
        int v_last_no = 0;
        OleDbCommand command = new OleDbCommand();
        command.Connection = connection;
        string query = @"select PARM_VALUE from soc_parm_mast where PARM_TYPE = '" + P_PRM_TYPE + "';";
        command.CommandText = query;
        OleDbDataReader reader = command.ExecuteReader();
        reader.Read();
        v_last_no = Int32.Parse(reader["PARM_VALUE"].ToString()) + 1;
        reader.Close();
        command.CommandText = @"update soc_parm_mast set PARM_VALUE = PARM_VALUE+1 where PARM_TYPE = " + P_PRM_TYPE + ";";
        command.ExecuteNonQuery();
        connection.Close();
        return v_last_no;
    }
}
}

但在执行过程中会出现错误

System.FormatException：输入字符串格式不正确 LIBRARY.Generate_no.gen_no（String P_PRM_TYPE）

Answer 1

command.CommandText = @"update soc_parm_mast set PARM_VALUE = PARM_VALUE+1 where PARM_TYPE = '" + P_PRM_TYPE + "';";

您在更新语句中缺少单引号

Answer 2

导致指定错误的行v_last_no = Int32.Parse(reader["PARM_VALUE"].ToString()) + 1;，如果输入不可转换，Int32.Parse将抛出FormatException。所以我强烈建议你使用Int32.TryParse()。然后代码如下：

public static int gen_no(string P_PRM_TYPE)
{
    using (OleDbConnection connection = new OleDbConnection(@"Connection string here"))
    {
        connection.Open();
        int v_last_no = 0;
        using (OleDbCommand command = new OleDbCommand())
        {
            command.Connection = connection;
            string query = @"select PARM_VALUE from soc_parm_mast where PARM_TYPE = @P_PRM_TYPE";
            command.CommandText = query;
            command.Parameters.AddWithValue("@P_PRM_TYPE", P_PRM_TYPE);
            OleDbDataReader reader = command.ExecuteReader();
            reader.Read();
            if (!Int32.TryParse(reader["PARM_VALUE"].ToString(), out v_last_no))
            {
                // Conversion failed, Show message if needed    
                // v_last_no will be 0
            }
            reader.Close();
        }
        using (OleDbCommand command = new OleDbCommand())
        {
            command.CommandText = @"update soc_parm_mast set PARM_VALUE = PARM_VALUE+1 where PARM_TYPE =@P_PRM_TYPE";
            command.Parameters.AddWithValue("@P_PRM_TYPE", P_PRM_TYPE);
            command.ExecuteNonQuery();
        } 
    }

    return v_last_no;
}

还有一个建议：在使用Concatenated字符串作为查询时要小心SQL注入。请改用参数化查询。

尝试从另一个类库中检索参数值

2 个答案: