即使数据存在于vb.net中的SqlDataReader中,也无法尝试读取数据

Question

这是我的代码,它给出了错误,查询返回特定项的值.

同样在数据库端查询返回行,即使我已经设置条件,如果读者有行然后只将它分配给一个变量,但仍然会抛出一个错误,例如.

dqty = sqlreader("qty")

码:

Private Function checkquantity(ByVal code As String, ByVal quan As Integer) As Boolean
    sqlcommand.CommandText = "select sum(qty) as qty from pos_stock_balance where item_code='" & code & "'"
    sqlcommand.Connection = AppsCon
    sqlreader = sqlcommand.ExecuteReader
    If sqlreader.HasRows Then

        dqty = sqlreader("qty")
        sqlreader.Close()

    Else
        sqlreader.Close()
    End If
    If quan > dqty Then
        Return False
    Else
        Return True

    End If
End Function

Answer 1

这是因为你在没有阅读的情况下直接访问数据,试试这个,

If sqlreader.HasRows Then
      If sqlreader.read()
        dqty = sqlreader("qty")
        sqlreader.Close()
       End If
Else
       sqlreader.Close()
End If

参考

清理过的代码版本,

Private Function checkquantity _
(ByVal code As String, ByVal quan As Integer) As Boolean

    try

    sqlcommand.CommandText = "select" _
    & "sum(qty) as qty from pos_stock_balance where item_code='" & code & "'"

    sqlcommand.Connection = AppsCon
    sqlreader = sqlcommand.ExecuteReader

    If sqlreader.read() Then
         dqty = sqlreader("qty")
    End If

    If quan > dqty Then
        Return False
    Else
        Return True
    End If

    Finally
       sqlreader.Close()
    End try

End Function

虽然我清理了你的代码,你的代码仍然容易受到sql注入.尝试使用参数化查询来避免这种情况