尝试从Access数据库中选择数据时，c＃中的OleDb异常“未为一个或多个必需参数提供值。”

Question

我有以下代码：

 public DataTable opencon(PAL.property objpal)
    {
        string query = "Select UserId,Firstname,UserType from TBL_USER_LOGIN where Username=@username and Password=@password and Status=1";
        OleDbCommand objcmd = new OleDbCommand();
        objcmd.CommandText = query;
        objcmd.Connection = oldbcon;
        oldbcon.Open();
        objcmd.Parameters.Add("@username", OleDbType.VarChar).Value = objpal.username;
        objcmd.Parameters.Add("@password", OleDbType.VarChar).Value = objpal.Password;
        DataTable dt = new DataTable();
        OleDbDataAdapter adp = new OleDbDataAdapter(objcmd);
        adp.Fill(dt);
        return dt;
    }

在这里，我想根据条件从表中获取一些值，但是当我运行此代码时，它显示以下错误：

即使我在@username和@password中传递了正确的参数值。 如何解决此错误？ 请帮忙。

Answer 1

尝试这个：

public DataTable opencon(PAL.property objpal)
{
    string query = "Select UserId,Firstname,UserType from TBL_USER_LOGIN where Username=? and Password=? and Status=1";
    OleDbCommand objcmd = new OleDbCommand();
    objcmd.CommandText = query;
    objcmd.Connection = oldbcon;
    oldbcon.Open();
    objcmd.Parameters.Add("@username", OleDbType.VarChar).Value = objpal.username;
    objcmd.Parameters.Add("@password", OleDbType.VarChar).Value = objpal.Password;
    DataTable dt = new DataTable();
    OleDbDataAdapter adp = new OleDbDataAdapter(objcmd);
    adp.Fill(dt);
    return dt;
}

Answer 2

尝试这个

字符串查询=“从[TBL_USER_LOGIN]中选择[UserId]，[Firstname]，[UserType]，其中[Username] =？和[Password] =？并且[Status] = 1”；