我需要从.dbf文件中提取数据并将其转换为xml.我写了一个例程,它做得很好.但是现在我们遇到了非常大的.dbf文件 – 比如2GB.此代码会对这些文件抛出OutOfMemoryException.
Public Function GetData() As DataTable
Dim dt As New DataTable(Name)
Dim sqlcommand As String= "Select * From MyTable"
Dim cn As New OleDbConnection(myconnectionstring)
Try
cn.Open()
Dim cmd As New OleDbCommand(sqlcommand,cn)
dt.Load(cmd.ExecuteReader())
Catch ex As Exception
Throw ex
Finally
dt.Dispose()
cn.Close()
cn.Dispose()
End Try
Return dt
问题是 – 如果我在我的计算机上通过Visual Studio在调试模式下针对相同的2GB .dbf文件运行相同的代码,则不会抛出任何异常.这几乎就像Visual Studio以不同的方式管理内存而应用程序单独执行.
反正有没有解决内存问题？我尝试过使用类似结果的DataAdapter.我在Visual Studio预期/设计中看到的这种行为是什么？
解决方法
数据表位于内存中,因此在大文件上会失败,或者根据文件的大小变慢.
您需要使用sqlDataReader按记录读取数据记录,并使用XmlWriter创建XML文件.
像这样的东西(未检查代码)
Public Sub WriteToXml(Dim xmlFileName As String,Dim connectionString)
Dim writer As XmlWriter
writer = XmlWriter.Create(xmlFileName)
Dim commandText As String= "Select * From MyTable"
Dim connection As New OleDbConnection(connectionString)
Try
connection.Open()
Dim command As New OleDbCommand(commandText,connection)
Dim reader As sqlDataReader
reader = myCommand.ExecuteReader()
While reader.Read()
write.WriteRaw("xml")
End While
Catch ex As Exception
Throw ex
Finally
connection.Close()
connection.Dispose()
End Try
End Sub