我有這個代碼插入數據到數據庫。我想檢查要插入的ID是否已經在數據庫中。但是如果它不在數據庫中,它應該被插入。但有一些錯誤,你能幫我解決嗎?現在如何檢查ID是否已存儲在數據庫中?
public void Add()
{
sc.Open();
try
{
cmd = new SqlCommand("Select idnum from TableVotersInfo Where [email protected]", sc);
cmd.Parameters.AddWithValue("@idnum", _idnum);
SqlDataReader rd = cmd.ExecuteReader();
if (rd.Read() == true)
{
MessageBox.Show("ID number already exist!");
rd.Close();
}
else
{
cmd = new SqlCommand("INSERT INTO TableVotersInfo (Education, idnum, FirstName, MiddleName, LastName, SchoolYear, ControlNum, VResult) VALUES (@ed, @idnum, @firstname, @middlename, @lastname, @schoolyear, @controlnum, 'Not Voted');", sc);
cmd.Parameters.AddWithValue("@id", _id);
cmd.Parameters.AddWithValue("@ed", _ed);
cmd.Parameters.AddWithValue("@idnum", _idnum);
cmd.Parameters.AddWithValue("@firstname", _firstname);
cmd.Parameters.AddWithValue("@middlename", _middlename);
cmd.Parameters.AddWithValue("@lastname", _lastname);
cmd.Parameters.AddWithValue("@schoolyear", _schoolyear);
cmd.Parameters.AddWithValue("@controlnum", _controlnum);
cmd.ExecuteNonQuery();
MessageBox.Show("Data Stored Successfully!");
FAddVoters._cleardata = cleardata;
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
sc.Close();
}
}
編輯 我的錯誤是There is already an open DataReader associated with this command which must be closed first.
。
更新
public void Update()
{
sc.Open();
try
{
cmd = new SqlCommand("UPDATE TableVotersInfo SET [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] WHERE [email protected]", sc);
cmd.Parameters.AddWithValue("@id", _id);
cmd.Parameters.AddWithValue("@ed", _ed);
cmd.Parameters.AddWithValue("@idnum", _idnum);
cmd.Parameters.AddWithValue("@firstname", _firstname);
cmd.Parameters.AddWithValue("@middlename", _middlename);
cmd.Parameters.AddWithValue("@lastname", _lastname);
cmd.Parameters.AddWithValue("@schoolyear", _schoolyear);
cmd.Parameters.AddWithValue("@controlnum", _controlnum);
int res = cmd.ExecuteNonQuery();
if (res > 0)
{
MessageBox.Show("Successfully Updated!");
FAddVoters._cleardata = cleardata;
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
sc.Close();
}
}
這個答案顯示了「INSERT如果不存在」最好的做法 - http://stackoverflow.com/questions/5288283/sql-server-insert-if-not-exists-best-practice –
只是刪除單來自idnum ='@ idnum'的引用是idnum = @ idnum –
我編輯了我的代碼。對不起,我搞砸了,我以爲我剛剛複製了添加方法。我在if(rd.Read()== true)之後複製了add和update方法lol –