Question

在我的数据库表中，我想创建不存在的新条目，如果它们存在则更新它们。我有一个表将UserID LernfeldID和Schoolyear链接到Marks。当UserID不匹配时，应该只插入数据库，这意味着该条目不存在。如果有条目，则应该更新。

我使用Datatable对象，因为它似乎适合我所阅读的内容。我想查看DBNull.Value，但它不起作用。我的数据库只接收SELECT语句。如果我使用for循环更新DataTable并将其发送回数据库，则可以正常工作。但是我仍然需要做＆＃34;条目存在＆＃34;校验。你可以帮帮我吗？

我的代码如下所示：

    public static void DB_GetMarks()
    {
        using (SqlConnection con = new SqlConnection(ConnectionString))
        {
            try
            {
                SqlCommand cmdQueryMarks = new SqlCommand();
                cmdQueryMarks.Connection = con;
                cmdQueryMarks.CommandText = "SELECT UserID, LernfeldID, SchuljahrID, Note "
                                           + "FROM UsersToLernfelder "
                                           + "WHERE USERID = @usrID "
                                           + "AND SchuljahrID = @YearID "
                                           + "ORDER BY LernfeldID ASC";
                cmdQueryMarks.Parameters.AddWithValue("@usrID", _UserID);
                cmdQueryMarks.Parameters.AddWithValue("@YearID", _YearID);

                SqlDataAdapter da = new SqlDataAdapter(cmdQueryMarks);

                DataTableMapping dtm = da.TableMappings.Add("Table", "UsersToLernfelder");
                dtm.ColumnMappings.Add("UserID", "User");
                dtm.ColumnMappings.Add("LernfeldID", "Lernfeld");
                dtm.ColumnMappings.Add("SchuljahrID", "Schuljahr");

                DataTable tbl = new DataTable();
                da.Fill(tbl);

                int i = 0;

                foreach (DataRow row in tbl.Rows)
                {
                    object value = row["UserID"];

                    if (value == DBNull.Value)
                    {
                        DataRow newEntry = tbl.NewRow();
                        newEntry["UserID"] = UserID;
                        newEntry["Lernfeld"] = i + 1;
                        newEntry["Schuljahr"] = YearID;
                        newEntry["Note"] = MarksArr[i];
                        tbl.Rows.Add(newEntry);
                    }
                    else
                    {
                        row["marks"] = MarksArr[i];
                    }

                    i++;
                }

                SqlCommandBuilder cmb = new SqlCommandBuilder(da);
                da.Update(tbl);
            }
            catch (Exception ex)
            {
                _Err = ex.Message;
            }
        }
    }

PS。这是我的第一篇文章，请原谅任何可能的错误

Answer 1

你看起来Merge命令。 this answer也会帮助你。

Answer 2

您无法获得Null Rows，因为您已使用@UserID过滤了记录

如果您想使用不存在的用户更新UsersToLernfelder，那么您应该有一个Users和Marks的列表。

   public static void DB_GetMarks(int _UserID, int _YearID)
    {

        Dictionary<int, double> MarksArr = new Dictionary<int, double>();

        MarksArr.Add(1, 50);
        MarksArr.Add(2, 49);
        MarksArr.Add(3, 48);
        using (SqlConnection con = new SqlConnection(""))
        {
            try
            {
                SqlCommand cmdQueryMarks = new SqlCommand();
                cmdQueryMarks.Connection = con;
                cmdQueryMarks.CommandText = "SELECT UserID, LernfeldID, SchuljahrID, Note "
                                           + "FROM UsersToLernfelder "
                                           + "WHERE USERID = @usrID "
                                           + "AND SchuljahrID = @YearID "
                                           + "ORDER BY LernfeldID ASC";
                cmdQueryMarks.Parameters.AddWithValue("@usrID", _UserID);
                cmdQueryMarks.Parameters.AddWithValue("@YearID", _YearID);

                SqlDataAdapter da = new SqlDataAdapter(cmdQueryMarks);

                DataTableMapping dtm = da.TableMappings.Add("Table", "UsersToLernfelder");
                dtm.ColumnMappings.Add("UserID", "User");
                dtm.ColumnMappings.Add("LernfeldID", "Lernfeld");
                dtm.ColumnMappings.Add("SchuljahrID", "Schuljahr");

                DataTable tbl = new DataTable();
                da.Fill(tbl);

                int i = 0;

                foreach (var item in MarksArr)
                {
                    DataRow Result = (from DataRow dr in tbl.Rows where Convert.ToInt32(dr["USERID"]) == item.Key select dr).FirstOrDefault();
                    if (Result == null)
                    {
                        DataRow newEntry = tbl.NewRow();
                        newEntry["UserID"] = item.Key;
                        newEntry["Lernfeld"] = i + 1;
                        newEntry["Schuljahr"] = _YearID;
                        newEntry["Note"] = item.Value;
                        tbl.Rows.Add(newEntry);
                    }
                    else
                    {
                        foreach (DataRow _dr in tbl.Rows)
                        {
                            if (Convert.ToInt32(_dr["UserID"]) == item.Key)
                            {
                                _dr["marks"] = item.Value;
                            }
                        }
                    }
                    i++;
                }

                SqlCommandBuilder cmb = new SqlCommandBuilder(da);
                da.Update(tbl);
            }
            catch (Exception ex)
            {
                _Err = ex.Message;
            }
        }
    }

c＃从数据库中过滤掉NULL行并更新existig行

2 个答案: