VB.NET 中的准备语句答案

【问题标题】：Prepared Statements in VB.NETVB.NET 中的准备语句
【发布时间】：2011-11-13 03:33:16
【问题描述】：

我是 vb.net 和 Microsoft SQL Server 2008 中准备好的语句的新手。我真的找不到任何好的资源来通过连接字符串连接到数据库并执行准备好的语句。有人可以给我看一个例子或指出一个可能有用的资源吗？

【问题讨论】：

标签： sql database vb.net prepared-statement

【解决方案1】：

Dim datOleReader As SqlDataReader
' Public con As New SqlConnection

Public Function CHECK_CONNECTION(ByVal CON As SqlConnection) As SqlConnection
    Try
        If CON.State = ConnectionState.Broken Or CON.State = ConnectionState.Closed Then
            CON.Open()
        End If
    Catch ex As Exception
        CON.Close()
        CON.Open()
    End Try

    Return CON
End Function

Public Function gGetMaxCode(ByVal strTable As String, ByVal strCode As String) As Long
    Dim cmdtext As New SqlCommand
    Try
        '  con = clsexe.CHECK_CONNECTION(con) #
        ' cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = "SELECT ISNULL(MAX(" & strCode & "),0)+1 FROM  " & strTable
        datOleReader = cmdtext.ExecuteReader(CommandBehavior.SingleRow)
        datOleReader.Read()
        If datOleReader.IsDBNull(0) Then
            Return 1
        Else
            Return datOleReader.Item(0)
        End If

    Catch ex As Exception
        MsgBox(ex.Message.ToString)
    Finally
        datOleReader.Close()
    End Try
End Function
Public Function gGetMaxCode(ByVal strTable As String, ByVal strCode As String, ByVal trans As SqlTransaction) As Long
    Dim cmdtext As New SqlCommand
    Try
        '  con = clsexe.CHECK_CONNECTION(con) #
        ' cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = "SELECT ISNULL(MAX(" & strCode & "),0)+1 FROM  " & strTable
        cmdtext.Transaction = trans
        datOleReader = cmdtext.ExecuteReader(CommandBehavior.SingleRow)
        datOleReader.Read()
        If datOleReader.IsDBNull(0) Then
            Return 1
        Else
            Return datOleReader.Item(0)
        End If

    Catch ex As Exception
        Throw ex
    Finally
        datOleReader.Close()
    End Try
End Function

   Public Function ExecuteQry(ByVal qry As String) As Boolean
    Dim cmdtext As New SqlCommand
    Try
        'con = cls.cnn #
        'cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = qry
        cmdtext.CommandType = CommandType.Text
        cmdtext.ExecuteNonQuery()
        cmdtext.Dispose()
        cmdtext = Nothing
        ErrCode = True
    Catch ex As Exception
        'gErrMsg()
        ErrCode = False
        MsgBox(ex.Message.ToString)
    Finally
        'con.Close()
    End Try
End Function
Public Function ExecuteQry(ByVal qry As String, ByVal trans As SqlTransaction) As Boolean
    Dim cmdtext As New SqlCommand
    Try
        'con = cls.cnn #
        'cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = qry
        cmdtext.CommandType = CommandType.Text
        cmdtext.Transaction = trans
        cmdtext.ExecuteNonQuery()
        cmdtext.Dispose()
        cmdtext = Nothing
    Catch ex As Exception
        Throw ex
        'gErrMsg()
        MsgBox(ex.Message.ToString)
    Finally
        'con.Close()
    End Try
End Function


Public Function ExecuteSelect(ByVal qry As String, ByVal trans As SqlTransaction) As SqlDataReader

    Dim cmdtext As New SqlCommand
    Try
        'con = cls.cnn #
        'cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = qry
        cmdtext.CommandType = CommandType.Text
        cmdtext.Transaction = trans
        ExecuteSelect = cmdtext.ExecuteReader()
        Return ExecuteSelect
        cmdtext.Dispose()
        cmdtext = Nothing

    Catch ex As Exception
        Throw ex
        'MsgBox(ex.Message.ToString)
    Finally
        'clsexe.ExecuteSelect.Close()
        'con.Close()
    End Try
End Function


Public Function Executescalar(ByVal qry As String, ByVal trans As SqlTransaction)

    Dim cmdtext As New SqlCommand
    Try
        'con = cls.cnn #
        'cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = qry
        cmdtext.CommandType = CommandType.Text
        cmdtext.Transaction = trans
        Executescalar = cmdtext.ExecuteScalar
        cmdtext.Dispose()
        cmdtext = Nothing

    Catch ex As Exception
        Throw ex
        ' MsgBox(ex.Message.ToString)
    Finally
        ' con.Close()
    End Try

End Function


Public Function ExecuteAdapter(ByVal qry As String, ByVal trans As SqlTransaction) As SqlDataAdapter
    Dim cmdtext As New SqlCommand
    Dim da As New SqlDataAdapter
    Try
        'con = cls.cnn #
        'cmdtext.Connection = con
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandTimeout = 0
        cmdtext.CommandText = qry
        cmdtext.Transaction = trans
        cmdtext.CommandType = CommandType.Text
        da.SelectCommand = cmdtext
        Return da
        cmdtext.Dispose()
        cmdtext = Nothing
    Catch ex As Exception
        Throw ex
        'MsgBox(ex.Message.ToString)
    Finally
        ' con.Close()
    End Try
End Function


Public Function Executedataset(ByVal qry As String) As DataSet
    Dim cmdtext As New SqlCommand
    Dim ds As New DataSet
    Dim da As New SqlDataAdapter
    Try
        'con = cls.cnn #
        'cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = qry
        cmdtext.CommandType = CommandType.Text
        da.SelectCommand = cmdtext
        da.Fill(ds)
        cmdtext.Dispose()
        cmdtext = Nothing
    Catch ex As Exception
        MsgBox(ex.Message.ToString)
    End Try
End Function

Public Function ExecuteProcedure(ByVal qry As String) As Boolean
    Dim cmdtext As New SqlCommand
    Try
        'con = cls.cnn #
        'cmdtext.Connection = con #
        cmdtext.Connection = CHECK_CONNECTION(con) ' #
        cmdtext.CommandText = qry
        cmdtext.CommandType = CommandType.StoredProcedure
        cmdtext.ExecuteNonQuery()
        cmdtext.Dispose()
        cmdtext = Nothing
    Catch ex As Exception
        MsgBox(ex.Message.ToString)
    End Try
End Function

【讨论】：

你能在这里添加更多细节吗？虽然我可以欣赏这个例子，但对一些片段的解释会很好。

【解决方案2】：

这里有一些简单的示例代码：

Using cn  As New SqlConnection("your connection string here"), _
      cmd AS New SqlCommand("SELECT * FROM Table WHERE ID= @ID", cn)

    cmd.Parameters.Add("@ID", SqlDbType.Int).Value = 12345

    cn.Open()
    Using rdr As SqlDataREader = cmd.ExecuteReader()
        While rdr.Read()
            'Do something with the record
        End While
        rdr.Close()
    End Using
End Using

当然需要导入 System.Data 和 System.Data.SqlClient。

【讨论】：

【解决方案3】：

准备好的语句只不过是包含在事务中的参数化 SqlCommand。

例如，这是一个Prepared Statement：

Using c As New SqlConnection(ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString)
   c.Open()
using mytransaction = c.BeginTransaction()

   Dim command = New SqlCommand("INSERT INTO yourtable(image) values (@image)", c)
   ''# this is specific to the FileUploadControl but the idea is to get the
   ''#image in a byte array; however you do it, it doesn't matter
    Dim buffer(FileUpload1.PostedFile.ContentLength) As Byte
    FileUpload1.PostedFile.InputStream.Read(buffer, 0, buffer.Length)
    command.Parameters.AddWithValue("@image", buffer)
    command.ExecuteNonQuery()    
 mytransaction .Commit()
End Using
End Using

【讨论】：

对不起，但是……我相信你错了？它们不需要事务，并且在允许服务器重用执行计划方面具有优势。 msdn.microsoft.com/en-us/library/…
@Basic 您描述的是存储过程。虽然所有存储过程都是预准备语句，但并非所有预准备语句都是存储过程。
@DavidSöderlund 我都知道（事实上，我链接的文档讨论了这两个）。我试图说明的一点是，Icarus 的回答似乎并不准确，例如我可以编译一个准备好的语句，允许服务器构建一个执行计划，然后多次重复使用它。这个答案完全省略了这种模式。
另外，AddWithValue() 也有一些严重的缺点。最好使用带有显式类型信息的 Add() 重载。