简单地说，我有一个应用程序，它有一个页面可以删除，然后每隔30秒将记录重新添加/刷新到一个表中。我有另一个页面，每45秒运行一次，读取表数据并构建图表。
问题是，在读取/查看页面中，每隔一段时间我得到一个0值（从最大计数），图表什么都没有显示。我有一种感觉，这种情况正在发生，因为删除页面删除了表中的所有记录但尚未刷新/重新添加它们的同时完成了读取。
我的应用程序中是否有一种方法可以在刷新表时暂缓读取？
最诚挚的问候， 安迪
下面的代码是在ASP.Net 4.5内置的Windows服务中运行的。它删除ActualPlot表中的所有记录，然后每30秒从文本文件刷新/添加新记录。我基本上需要阻止（锁定？）任何用户在删除和刷新记录时读取ActualPlot表。你能帮我改变我的代码吗？
private void timer1_Tick(object sender, ElapsedEventArgs e)
{
// Open the SAP text files, clear the data in the tables and repopulate the new SAP data into the tables.
var cnnString = ConfigurationManager.ConnectionStrings["TaktBoardsConnectionString"].ConnectionString;
SqlConnection conn = new SqlConnection(cnnString);
SqlConnection conndetail = new SqlConnection(cnnString);
SqlConnection connEdit = new SqlConnection(cnnString);
SqlCommand cmdGetProductFile = new SqlCommand();
SqlDataReader reader;
string sql;
// Delete all the records from the ActualPlot and the ActualPlotPreload tables. We are going to repopulate them with the data from the text file.
sql = "DELETE FROM ActualPlotPreload";
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.ExecuteNonQuery();
}
catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Delete Error:";
msg += ex.Message;
Library.WriteErrorLog(msg);
}
finally
{
conn.Close();
}
sql = "DELETE FROM ActualPlot";
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.ExecuteNonQuery();
}
catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Delete Error:";
msg += ex.Message;
Library.WriteErrorLog(msg);
}
finally
{
conn.Close();
}
// Read the SAP text file and load the data into the ActualPlotPreload table
sql = "SELECT DISTINCT [BoardName], [ProductFile], [ProductFileIdent] FROM [TaktBoards].[dbo].[TaktBoard] ";
sql = sql + "JOIN [TaktBoards].[dbo].[Product] ON [Product].[ProductID] = [TaktBoard].[ProductID]";
cmdGetProductFile.CommandText = sql;
cmdGetProductFile.CommandType = CommandType.Text;
cmdGetProductFile.Connection = conn;
conn.Open();
reader = cmdGetProductFile.ExecuteReader();
string DBProductFile = "";
string DBTischID = "";
string filepath = "";
string[] cellvalues;
DateTime dt, DateCheckNotMidnightShift;
DateTime ldSAPFileLastMod = DateTime.Now;
string MyDateString;
int FileRecordCount = 1;
while (reader.Read())
{
DBProductFile = (string)reader["ProductFile"];
DBTischID = (string)reader["ProductFileIdent"];
filepath = "c:\\inetpub\\wwwroot\\WebApps\\TaktBoard\\FilesFromSAP\\" + DBProductFile;
FileInfo fileInfo = new FileInfo(filepath); // Open file
ldSAPFileLastMod = fileInfo.LastWriteTime; // Get last time modified
try
{
StreamReader sr = new StreamReader(filepath);
FileRecordCount = 1;
// Populate the AcutalPlotPreload table from with the dates from the SAP text file.
sql = "INSERT into ActualPlotPreload (ActualDate, TischID) values (@ActualDate, @TischID)";
while (!sr.EndOfStream)
{
cellvalues = sr.ReadLine().Split(';');
if (FileRecordCount > 1 & cellvalues[7] != "")
{
MyDateString = cellvalues[7];
DateTime ldDateCheck = DateTime.ParseExact(MyDateString, "M/dd/yyyy", null);
DateTime dateNow = DateTime.Now;
string lsDateString = dateNow.Month + "/" + dateNow.Day.ToString("d2") + "/" + dateNow.Year;
DateTime ldCurrentDate = DateTime.ParseExact(lsDateString, "M/dd/yyyy", null);
string lsTischID = cellvalues[119];
if (ldDateCheck == ldCurrentDate)
{
try
{
conndetail.Open();
SqlCommand cmd = new SqlCommand(sql, conndetail);
cmd.Parameters.Add("@ActualDate", SqlDbType.DateTime);
cmd.Parameters.Add("@TischID", SqlDbType.VarChar);
cmd.Parameters["@TischID"].Value = cellvalues[119];
MyDateString = cellvalues[7] + " " + cellvalues[55];
dt = DateTime.ParseExact(MyDateString, "M/dd/yyyy H:mm:ss", null);
cmd.Parameters["@ActualDate"].Value = dt;
// Ignore any midnight shift (12am to 3/4am) units built.
DateCheckNotMidnightShift = DateTime.ParseExact(cellvalues[7] + " 6:00:00", "M/dd/yyyy H:mm:ss", null);
if (dt >= DateCheckNotMidnightShift)
{
cmd.ExecuteNonQuery();
}
}
catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Insert Error:";
msg += ex.Message;
Library.WriteErrorLog(msg);
}
finally
{
conndetail.Close();
}
}
}
FileRecordCount++;
}
sr.Close();
}
catch
{ }
finally
{ }
}
conn.Close();
// Get the unique TischID's and ActualDate from the ActualPlotPreload table. Then loop through each one, adding the ActualUnits
// AcutalDate and TischID to the ActualPlot table. For each unique TischID we make sure that we reset the liTargetUnits to 1 and
// count up as we insert.
SqlCommand cmdGetTischID = new SqlCommand();
SqlDataReader readerTischID;
int liTargetUnits = 0;
string sqlInsert = "INSERT into ActualPlot (ActualUnits, ActualDate, TischID) values (@ActualUnits, @ActualDate, @TischID)";
sql = "SELECT DISTINCT [ActualDate], [TischID] FROM [TaktBoards].[dbo].[ActualPlotPreload] ORDER BY [TischID], [ActualDate] ASC ";
cmdGetTischID.CommandText = sql;
cmdGetTischID.CommandType = CommandType.Text;
cmdGetTischID.Connection = conn;
conn.Open();
readerTischID = cmdGetTischID.ExecuteReader();
DBTischID = "";
DateTime DBActualDate;
string DBTischIDInitial = "";
while (readerTischID.Read())
{
DBTischID = (string)readerTischID["TischID"];
DBActualDate = (DateTime)readerTischID["ActualDate"];
if (DBTischIDInitial != DBTischID)
{
liTargetUnits = 1;
DBTischIDInitial = DBTischID;
}
else
{
liTargetUnits++;
}
try
{
conndetail.Open();
SqlCommand cmd = new SqlCommand(sqlInsert, conndetail);
cmd.Parameters.Add("@ActualUnits", SqlDbType.Real);
cmd.Parameters.Add("@ActualDate", SqlDbType.DateTime);
cmd.Parameters.Add("@TischID", SqlDbType.VarChar);
cmd.Parameters["@TischID"].Value = DBTischID;
cmd.Parameters["@ActualDate"].Value = DBActualDate;
cmd.Parameters["@ActualUnits"].Value = liTargetUnits;
cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
}
catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Insert Error:";
msg += ex.Message;
Library.WriteErrorLog(msg);
}
finally
{
conndetail.Close();
}
}
conn.Close();
Library.WriteErrorLog("SAP text file data has been imported.");
}
答案 0 :(得分：1)
如果在删除之后立即重新添加数据（基本上你知道在清空表之前要重新添加什么），你可以在同一个SQL事务中同时进行这两个操作，这样数据就可以用到仅在重新添加时才显示其他页面。
我的意思是这样的：
public bool DeleteAndAddData(string connString)
{
using (OleDbConnection conn = new OleDbConnection(connString))
{
OleDbTransaction tran = null;
try
{
conn.Open();
tran = conn.BeginTransaction();
OleDbCommand deleteComm = new OleDbCommand("DELETE FROM Table", conn);
deleteComm.ExecuteNonQuery();
OleDbCommand reAddComm = new OleDbCommand("INSERT INTO Table VALUES(1, 'blabla', 'etc.'", conn);
reAddComm.ExecuteNonQuery();
tran.Commit();
}
catch (Exception ex)
{
tran.Rollback();
return false;
}
}
return true;
}
答案 1 :(得分：0)
如果您的查询执行时间过长，则可以以7.5秒的差异启动两个查询，因为当读/写完成3个周期时，每90秒发生一次冲突，并且读取/视图完成2个周期。
话虽如此，它不是一个万无一失的解决方案，只是一个基于假设的技巧，万一你不能完全确定读/写周期是不会发生读/写周期发生了，尝试考虑使用Read Lock。我建议您阅读Understanding how SQL Server executes a query和Locking in the Database Engine
希望有所帮助。
答案 2 :(得分：0)
我会尝试一些事情：
确保您在一次交易中发生DELETE + INSERT次操作：
BEGIN TRAN
DELETE FROM ...
INSERT INTO ...
COMMIT
如果这不是忙表，请尝试锁定提示SELECT语句。例如：
SELECT ...
FROM Table
WITH (UPDLOCK, HOLDLOCK)
如果更新事务在SELECT语句运行时启动，则会导致该事务等待SELECT完成。不幸的是，它也会阻止其他SELECT语句，但你不会冒险阅读脏数据。
答案 3 :(得分：0)
我无法解决这个问题，但我更改了代码，因此程序没有删除ActualPlot表中的所有行，而是检查行是否在那里，如果没有从文本文件中添加新行。