VB.NET积分系统

我有一个MySQL数据库设置：VB.NET积分系统

表核算：

ID：1
名称：唐尼
积分：600

我有一个名为购买按钮点击时运行如下

If credits.Text <= 0 Then 
      MsgBox("Geen credits meer.") 
     Else 

      Dim conn As MySqlConnection 
      conn = New MySqlConnection 
      conn.ConnectionString = "server=xxx;port=3306; user id=xxx; password=xxx; database=xxx" 
      Try 
       conn.Open() 
      Catch myerror As MySqlException 
       MsgBox("error connecting to database") 
      End Try 
      Dim myadapter As New MySqlDataAdapter 

      Dim sqlquery = "UPDATE account SET credits = credits -700 WHERE id='" & Trim(id.Text) & "'" 

      Dim mycommand As New MySqlCommand() 
      mycommand.Connection = conn 
      mycommand.CommandText = sqlquery 
      myadapter.SelectCommand = mycommand 
      mycommand.ExecuteNonQuery() 
      Try 
       conn.Close() 
      Catch myerror As MySqlException 
       MessageBox.Show("Cannot connect to database: " & myerror.Message) 
      Finally 
       conn.Dispose() 
      End Try 

     End If

例如，我有600学分在我的帐户。我想购买一个价格为700美元的产品。该系统说它不可能，因为你只有600个学分。目前的代码显示-100积分，但是我怎样才能检查并显示错误消息呢？

来源

2015-04-13 Jerry Tom

我建议创建一个存储过程来执行此操作，返回值指示成功或失败。检查可用的信用，并在交易中扣除金额（如果信用额度足够）。 –

我想你应该首先读取可用的信用，然后验证是否足够，如果不是弹出消息，则请继续更新！ –

您可以只需添加一个功能到您的程序，以检查是否有足够的学分：

Public Function checkCredits(ByVal creditsNeeded As Int32, ByVal id As String) As Boolean 
    Dim conn As New MySqlConnection 
    conn.ConnectionString = "server=xxx;port=3306; user id=xxx; password=xxx; database=xxx" 
    conn.Open() 

    Dim mycommand As New MySqlCommand() 
    With mycommand 
     .Connection = conn 
     .CommandType = CommandType.Text 
     .CommandText = "SELECT credits FROM account WHERE id = @id" 
     .Parameters.Add("@id", MySqlDbType.VarChar).Value = id 
    End With 

    Dim creditsAvailable As Int32 = mycommand.ExecuteScalar 
    conn.Close() 

    If creditsAvailable >= creditsNeeded Then 
     Return True 
    Else 
     Return False 
    End If 
End Function

然后调整上述代码中使用它：

If credits.Text <= 0 Then 
     MsgBox("Geen credits meer.") 
    Else 
     If checkCredits(700, id.Text) Then 

      Dim conn As MySqlConnection 
      conn = New MySqlConnection 
      conn.ConnectionString = "server=xxx;port=3306; user id=xxx; password=xxx; database=xxx" 
      Try 
       conn.Open() 
      Catch myerror As MySqlException 
       MsgBox("error connecting to database") 
      End Try 
      Dim myadapter As New MySqlDataAdapter 

      Dim sqlquery = "UPDATE account SET credits = credits -700 WHERE id='" & Trim(id.Text) & "'" 

      Dim mycommand As New MySqlCommand() 
      mycommand.Connection = conn 
      mycommand.CommandText = sqlquery 
      myadapter.SelectCommand = mycommand 
      mycommand.ExecuteNonQuery() 
      Try 
       conn.Close() 
      Catch myerror As MySqlException 
       MessageBox.Show("Cannot connect to database: " & myerror.Message) 
      Finally 
       conn.Dispose() 
      End Try 
     Else 
      MessageBox.Show("Not Enough Credits") 
     End If 
    End If

来源

2015-04-13 00:46:06

VB.NET积分系统

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