VB.NET使用中

Question

Can I do:

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

with 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

Because in the SQLSelect function, at the end of the using, the connection is broken! So I have an error when I try to connect to the second query.

Thx

Answer 1

Simply use a DAL pattern like this:

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

...

Calling code:

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