VB.NET 使用中使用答案

【问题标题】：VB.NET Using in UsingVB.NET 使用中使用
【发布时间】：2015-09-08 22:33:57
【问题描述】：

我能做到吗：

using connection
myDt1 = sqlSelect(connection, sql)
myDt2 = sqlSelect(connection, sql)
end using

使用 SQLSelect ：

Public Shared Function SQLSelect(ByVal provider As SqlConnection, ByVal strSQL As String, ByVal ParamArray params() As SqlParameter) As DataTable
Using connection = provider

SQLSelect = New DataTable

Dim dtReader As SqlDataReader
Dim command As SqlCommand = CreateSQLCommand(provider, strSQL,  params)

Try
    connection.Open()
    dtReader = command.ExecuteReader()
    SQLSelect.Load(dtReader)
    dtReader.Close()
Catch ex As Exception
    SQLSelect = Nothing
Finally
    'If connection.State = ConnectionState.Open Then
    '    connection.Close()
    'End If
    command.Dispose()
End Try

End Using '<--- Here drop connection
Return SQLSelect

因为在SQLSelect函数中，在使用结束时，连接断开了！所以当我尝试连接到第二个查询时出现错误。

谢谢

【问题讨论】：

您正在关闭 SqlSelect 中的连接。Using 的全部意义在于为您关闭和处理连接。
这两行忘记注释了，drop connection append在en using end上，很奇怪，参数是ByVal，不是吗？
如果我每次都传递连接字符串而不是sqlconnection会更好吗？
您最好将 ~connection.Open()~ 从 SqlSelect 中取出并传递给 SqlSelect 一个打开的连接。同时从 SqlSelect 中删除 Using 和 EndUsing
最后一个问题，如果我在不同的类中有 3 个函数：-Main() -> 调用例如 ListAllData() -ListAllData -> execute SQLSelect(sqlconnection, parameters) -> which open connection and execute the query in the last classe with SQLSelect ---- -SQLSelect -> which execute 是正确的和好的练习？

标签： vb.net data-access-layer using sqlconnection

【解决方案1】：

只需像这样使用 DAL 模式：

Public Class DataAccessLayer
    'Implements IDataAccessLayer

    #Region "Members"

    Private ReadOnly connectionString As String
    Private ReadOnly configuration As IConfiguration
    Private ReadOnly exceptionHandler As IExceptionHandler

    #End Region

    #Region "Constructors"
    Public Sub New()
        Me.New(New Configuration(), New ExceptionHandler())
    End Sub

    Public Sub New(configuration As IConfiguration, exceptionHandler As IExceptionHandler)
        ' You can just pass in a ConnectionString, instead of my IConfiguration
        connectionString = configuration.GetDefaultConnectionString()
        'Me.exceptionHandler = exceptionHandler
    End Sub

    #End Region

    #Region "Opening and Closing Connection"

    Public Function GetConnection() As SqlConnection
        Dim conn = New SqlConnection(connectionString)
        Try
            conn.Open()
        Catch ex As SqlException
            'exceptionHandler.LogExceptions(ex, Nothing)
        Catch ex As Exception
            'exceptionHandler.LogExceptions(ex, Nothing)
        End Try
        Return conn
    End Function

    #End Region

    #Region "Stored Procedure Calls"

    Public Function TestConnection() As Boolean
        Try
            Dim conn = New SqlConnection(connectionString)
            conn.Open()
            conn.Close()
        Catch
            Return False
        End Try
        Return True
    End Function

    Public Function CallAStoredProcExample() As Boolean
        Dim codeObject As CodeObject = Nothing
        Try
            Using conn = Me.GetConnection()
                Using sqlCommand = New SqlCommand("sp_GetCodeByCodeID", conn)
                    sqlCommand.CommandType = CommandType.StoredProcedure
                    sqlCommand.Parameters.AddWithValue("@CodeId", 1)

                    Using dr = sqlCommand.ExecuteReader()
                        While dr.Read()
                            codeObject = New CodeObject(dr, True)
                        End While
                    End Using
                End Using
            End Using
        Catch ex As Exception
            Return False
        End Try
        Return True
    End Function
End Class

...

调用代码：

Dim DAL = New DataAccessLayer(yourConnectionString, Nothing)
DAL.CallAStoredProcExample()

【讨论】：