Question

我认为这不是一项艰巨的任务。

用户参加测验，然后出于任何原因决定重新参加测验。

我们的要求是在将结果插入SurveyAnswers表之前删除此用户已经完成的测验结果。

以下代码旨在删除属于试图重新参加测验然后插入当前结果的用户的每个questionId（qid）的现有结果。

这应该在一个操作中。

然后，如果当前没有结果，则插入当前测验的结果。

代码未插入或删除。

非常感谢您的帮助。

这是我的代码：

Private Sub SaveAnswer(ByVal qid As Integer, ByVal cid As Integer, ByVal ct As String, ByVal cscore As Integer)
    Dim al As ArrayList = CType(Session("AnswerList"), ArrayList)

    If al Is Nothing Then
        Response.Redirect("List.aspx")
    End If

    Dim cnn As New SqlConnection(ConfigurationManager.ConnectionStrings("DBConnectionString").ConnectionString)

    Dim cmd As New SqlCommand("IF EXISTS(SELECT QuestionId FROM SurveyAnswers WHERE questionId = @qid and UserName = @cuser " & _
                           "BEGIN delete from SurveyAnswers where UserName=@cuser and QuestionId=@qid " & _
                           "insert into surveyanswers(QuestionID,ChoiceID,ChoiceText,Username,dateTaken) values(@qid,@cid,@ct,@cuser,getDate()) END " & _
                           "Else BEGIN insert into surveyanswers(QuestionID,ChoiceID,ChoiceText,Username,dateTaken) values(@qid,@cid,@ct,@cuser,getDate()) END", cnn)
    Dim p1 As New SqlParameter("@qid", qid)
    Dim p2 As New SqlParameter("@cid", IIf(cid = 0, DBNull.Value, cid))
    Dim p3 As New SqlParameter("@ct", IIf(ct = "", DBNull.Value, ct))
    Dim p4 As New SqlParameter("@cuser", Session("UserName"))
    cmd.Parameters.Add(p1)
    cmd.Parameters.Add(p2)
    cmd.Parameters.Add(p3)
    cmd.Parameters.Add(p4)
    cnn.Open()
    cmd.ExecuteNonQuery()
    cnn.Close()
End Sub

Answer 1

以下是根据OP的要求提出答复的评论：

if exists ( select 42 from SurveyAnswers where ... )
  begin
  delete SurveyAnswers where ...
  end;
insert into SurveyAnswers ...

除此之外：请注意，您所做的事情不是原子的，除非它以适当的隔离级别包含在事务中。虽然单个用户不可能同时多次回答相同的调查问题，但您应该了解该问题并明确决定处理或忽略它。我同意在存储过程中实现它，例如：

create procedure dbo.InsertSurveyAnswer
  -- NB: The prior answer, if any, is deleted.
  @QuestionId as Int,
  @ChoiceId as Int,
  @ChoiceText as NVarChar(64),
  @Username as NVarChar(64)
  as

  set nocount on;

  set transaction isolation level serializable;
  begin transaction;

  -- Attempt to delete any prior answer for this user/question.
  delete from SurveyAnwers
    where Username = @Username and QuestionId = @QuestionId;

  -- Save the new answer.
  insert into SurveyAnswers
    ( QuestionId, ChoiceId, ChoiceText, Username, DateTaken ) values
    ( @QuestionId, @ChoiceId, @ChoiceText, @Username, GetDate() );

  commit transaction;

正如Martin Smith所建议的那样，你可能只是简单地执行delete而不是浪费资源来确定是否需要它。如果您有理由知道是否删除了某行，则可以在@@RowCount之后检查delete的值。

如果存在记录，请将其删除并插入新记录。为什么这不起作用？

1 个答案: