应用程序中操作数据库时如何使用事务？

Question

刚才在论坛上看了一个帖子“主　　题：  数据库的脆弱，请各路高手看一看。 ”
其中在很多回复的帖子中都提到在操作数据库时使用事务，我想请问如何在应用程序中使用事务？例如：我要从数据库中选择一些数据，使用如下语句：
ADOQuery1.SQL.Clear;
ADOQuery1.SQL.Add('select * from Mytable');
ADOQuery1.Active := True;
如果要是使用事务的话，还需要添加什么代码？另外，对数据库的任何操作都使用事务有必要吗？性能会提高吗？使用事务有什么原则吗？

Answer 1

/保存事件
procedure TFareFram.ToolButton2Click(Sender: TObject);
begin
  inherited;
    wwIncrementalSearch1.SetFocus;
    if   BookingState then
    begin
        if CheckData  then
        begin
            DMFreights.DataSource3.AutoEdit:=false;
            DMFreights.DataSource3.AutoEdit:=false;
            //Application.MessageBox('数据保存成功！','提示',MB_OK+MB_ICONINFORMATION);
            ToolButton2.Enabled:=false;
            ToolButton3.Enabled:=false;
            slkDBGrid1.ReadOnly:=true;
            slkDBGrid2.ReadOnly:=true;
            ToolButton6.Enabled:=false;            CanEditComponent(10,false);
            //added by jxp
            slkState := true;
        end
        else
        begin
            Application.MessageBox('单价没有没有填写！','提示',MB_OK+MB_ICONINFORMATION);
        end;
    end
    else
    begin
        Application.MessageBox('提单还处于撤载或归档状态！','提示',MB_OK+MB_ICONINFORMATION);
    end;
end;
一段我正在做的代码！

Answer 2

呵呵 主要部分没写
function TFareFram.CheckData : Boolean;
var
    Connection:TADOConnection;
begin
    result:=false;
    Connection:= TADOConnection.Create(self);
    Connection:=GetConnection;
    Connection.BeginTrans;// /开始事务
    result:=true;
    try
         if DMFreights.Queryfreight.RecordCount>0 then
         begin
            with DMFreights.Queryfreight do
            begin
                if VarIsNull(FieldValues['Unit_Price']) or VarIsNull(FieldValues['Account'])or VarIsEmpty(FieldValues['Unit_Price'])or VarIsEmpty(FieldValues['Account']) or VarIsNull(FieldValues['freight_name'])or VarIsEmpty(FieldValues['freight_name'])  then
                begin
                    result:=false;
                    slkDBGrid1.SetFocus;
                    connection.RollbackTrans;//事务回卷
                    exit;
                end
                else
                begin
                    UpdateBatch;
                    refresh;
                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['Unit_Price']) or VarIsNull(FieldValues['Account'])or VarIsEmpty(FieldValues['Unit_Price'])or VarIsEmpty(FieldValues['Account']) or VarIsNull(FieldValues['freight_name'])or VarIsEmpty(FieldValues['freight_name']) then
                    begin
                        result:=false;
                        slkDBGrid2.SetFocus;
                        connection.RollbackTrans;//事务回卷
                        exit;
                    end
                    else
                    begin
                        UpdateBatch;
                        Refresh ;
                    end;
                end;
            end
            else
            begin
                with DMFreights.Queryfreight1 do
                begin
                    UpdateBatch;
                    refresh;
                end;
            end;     end;
    Connection.CommitTrans;
    except
        Connection.RollbackTrans;
    end;end;

Answer 3

starttransaction
commit
rollback