如何防止多用户同时修改一条记录？

Question

在多用户使用时，某一条记录不让多用户同时修改。如何做？
sql server 2000
是否使用事务处理呢？如何使用？事务放在哪里？
谢谢

Answer 1

function TFareFram.CheckData : Boolean;
begin
    result:=false;
    if DMFreights.Queryfreight.Connection.InTransaction then
       DMFreights.Queryfreight.Connection.RollbackTrans;
    DMFreights.Queryfreight.Connection.BeginTrans;// /开始事务     try
        // Connection.BeginTrans;// /开始事务
         if DMFreights.Queryfreight.RecordCount>0 then
         begin
            with DMFreights.Queryfreight do
            begin
                if VarIsNull(FieldValues['Payer']) or VarIsEmpty(FieldValues['Payer'])or VarIsNull(FieldValues['Account'])or VarIsEmpty(FieldValues['Account']) or VarIsNull(FieldValues['freight_name'])or VarIsEmpty(FieldValues['freight_name']) or
                   VarIsNull(FieldValues['Remained'])or VarIsEmpty(FieldValues['Remained']) then
                begin
                    result:=false;
                    slkDBGrid1.SetFocus;
                    DMFreights.Queryfreight.Connection.RollbackTrans;
                    exit;
                end
                else
                begin
                    if  DMFreights.Queryfreight.FieldByName('Account').AsFloat = 0 then
                    begin
                      result:=false;
                      slkDBGrid2.SetFocus;
                      DMFreights.Queryfreight.Connection.RollbackTrans;
                      exit;
                    end
                    else
                    begin
                      UpdateBatch;
                      Refresh
                    end;
                end;
            end;
         end
         else
         begin
            with DMFreights.Queryfreight do
            begin
                UpdateBatch;
                refresh;
            end;
         end;        if   Panel1.Visible= true then
        begin
            if DMFreights.Queryfreight1.RecordCount>0 then
            begin
                with DMFreights.Queryfreight1 do
                begin
                    if VarIsNull(FieldValues['Payer'])or VarIsEmpty(FieldValues['Payer']) or VarIsNull(FieldValues['Account'])or VarIsEmpty(FieldValues['Account']) or VarIsNull(FieldValues['freight_name'])or VarIsEmpty(FieldValues['freight_name']) or
                       VarIsNull(FieldValues['Remained'])or VarIsEmpty(FieldValues['Remained']) then
                    begin
                        result:=false;
                        slkDBGrid2.SetFocus;
                        DMFreights.Queryfreight.Connection.RollbackTrans;
                        exit;
                    end
                    else
                    begin
                      if  DMFreights.Queryfreight1.FieldByName('Account').AsFloat = 0 then
                      begin
                        result:=false;
                        slkDBGrid2.SetFocus;
                        DMFreights.Queryfreight.Connection.RollbackTrans;
                        exit;
                      end
                      else
                      begin
                        UpdateBatch;
                        Refresh
                      end;
                    end;
                end;
            end
            else
            begin
                with DMFreights.Queryfreight1 do
                begin
                    UpdateBatch;
                    refresh;
                end;
            end;
     end;
    DMFreights.Queryfreight.Connection.CommitTrans;
    except
      DMFreights.Queryfreight.Connection.RollbackTrans;
      exit;
    end;
    result:=true;
end;

Answer 2

上面的代码太多了，是不是有必要这么多代码呢。
我使用的是ado连接到sql 20000上的。
有的说使用事务处理如下：  if (not adoconnection1.intransaction) then
  begin
    adoconnection1.begintrans;
  end ;
  try
    //你的代码
    adoconnection1.committrans;
  except
    adoconnection1.rollbacktrans;
 end;但不知道上面的这些语句是放在哪个控件的哪个属性中？

Answer 3

放在adoquery中的beforepost事件里吧

Answer 4

不需要事务处理，事物只是为了保证数据的一致性 ；
Sql Server 2000 在更新表时会自动锁表，也就是每个时间单位最多只有一个用户更新表

Answer 5

sqlserver会自动设置的，sqlserver是记录级锁定吧

Answer 6

sqlserver是自动锁定当前记录的，但能不能在多用户下同时修改一条记录时，有什么提示呢？
我发现是第1位修改的数据被系统接受，而其它用户再修改时，虽然不接受，但也没有什么提示，这样总觉得不怎么方便。

Answer 7

上面 mengxianbao1521(代码优化)老兄就用到了异常，语法是try..except..end;
作用是当try块中的代码在执行过程中发生错误（也就是异常），则执行except块中的内容，而发生异常后的语句块不在执行，直接执行end后的语句。目的是要增加代码的健壮性和容错性，使程序发生异常时不至于退出。