转：ADOQuery代替ClientDataSet做3-Tier系统

ADOQuery代替ClientDataSet做3-Tier系统

2009年09月23日 星期三 11:16

3-Tier的系统我们一般用Midas的TClientDataSet,它搭配BDE的TQuery效率还可以，毕竟是一家的;但搭配TADOQuery就慢了很多，大概9倍，因为不晓得人家的资料存储格式，只能一个Field一个Field读出来再用TDataSetProvider打包成Data:OLEVariant; ADO2.5提供了一个_Stream组件，配合BatchUpdate,可以做到TClientDataSet的功能,它的效率可以达到与TClientDataSet+TQuery一样: 1.Client给SQL到Server,Server用TADOQuery获取资料，然后Save到_Stream,返回； 2.Client用_Stream接收Server返回资料，给TADOQuery，用户可以随意增/删/改； 3.Client把用户修改后的资料Save到_Stream,传给Server(我现在还没办法只把异动资料存到_Stream,它把没有修改的资料也Save进去了，因为在WAN上跑时资料量对效率影响大；一种方法是存为XML格式，再用XML DOM组件去解析，把没修改的资料删掉，看各位还有更好的方法没有?); 4.Server用_Stream接收Client的修改资料，给TADOQuery，把FilterGroup设为fgPendingRecords，可以分析资料的增/删/改情况，处理企业逻辑，最后调用UpdateBatch保存资料。 5.Client在Call Server保存成功后，也调用UpdateBatch,使资料与实际一致，因为TADOQuery没有联接Connection,因此UpdateBatch相当于TClientDataSet的ClearChangeLog Server端的代码(Com+): function TEOStudent.ReadADOData(const ASQL: WideString): OLEVariant; var    AStream:_Stream;    MS1:TMemoryStream;    V:OLEVariant;    P:Pointer; begin    try      ADOConnection.Close;      ADOQuery.Close;      ADOQuery.SQL.Text:=ASQL;      ADOQuery.Open;      AStream:=CoStream.Create;      OLEVariant(ADOQuery.Recordset).Save(AStream,adPersistADTG);      ADOQuery.Close;      AStream.Position:=0;      V:=AStream.Read(AStream.Size);      MS1:=TMemoryStream.Create;      try        P:=VarArrayLock(V);        try          MS1.Size:=VarArrayHighBound(V,1)+1;          Move(P^,MS1.Memory^,MS1.Size);        finally          VarArrayUnLock(V);        end;        Result:=VarArrayCreate([0,MS1.Size-1],varByte);        P:=VarArrayLock(Result);        try          Move(MS1.Memory^,P^,MS1.Size);        finally          VarArrayUnLock(Result);        end;      finally        MS1.Free;      end;      SetComplete;    except      SetAbort;      Raise;    end; end; procedure TEOStudent.SaveADOData(AData: OLEVariant); var    AStream:_Stream;    AR:_Recordset; begin    try      ADOQuery.Close;      AStream:=CoStream.Create;      AStream.Open(EmptyParam,adModeUnknown,adOpenStreamUnspecified, ‘‘, ‘‘);      AStream.Type_:=adTypeBinary;      AStream.Write(AData);      AStream.Position:=0;      AR:=_Recordset(CoRecordset.Create);      AStream.Position:=0;      AR.Open(AStream,EmptyParam,adOpenKeyset,adLockBatchOptimistic,0);      ADOConnection.Close;      ADOConnection.Open;      AR.Set_ActiveConnection(ADOConnection.ConnectionObject);      ADOQuery.Recordset:=ADOInt._Recordset(AR); {     ADOQuery.FilterGroup:=fgPendingRecords;      ADOQuery.Filtered:=true;      try        ADOQuery.First;        while not ADOQuery.Eof do        begin          case ADOQuery.UpdateStatus of            usModified:ShowMessage(    VarToStr(ADOQuery.FieldByName(‘SeqNo‘).OldValue)+‘:‘+    ADOQuery.FieldByName(‘SeqNo‘).asString);          end;          ADOQuery.Next;        end;      finally        ADOQuery.Filtered:=false; //stateless      end;}      ADOQuery.UpdateBatch;      ADOConnection.Close;      SetComplete;    except      SetAbort;      Raise;    end; end; Client端，Form上放一个TADOQuery,不用连接Connection: 获取资料 procedure TForm1.Button5Click(Sender: TObject); var    V:OLEVariant;    AR:_Recordset;    AStream:_Stream;    MS1:TMemoryStream;    P:Pointer;    s:string; begin    DCOM.Connected:=true;    try      s:=‘‘;      V:=DCOM.AppServer.ReadADOData(‘select * from FORMDD‘);      MS1:=TMemoryStream.Create;      try        MS1.Size:=VarArrayHighBound(V,1)+1;        P:=VarArrayLock(V);        try          Move(P^,MS1.Memory^,MS1.Size);        finally          VarArrayUnLock(V);        end;        V:=VarArrayCreate([0,MS1.Size-1],varByte);        P:=VarArrayLock(V);        try          Move(MS1.Memory^,P^,MS1.Size);        finally          VarArrayUnLock(V);        end;      finally        MS1.Free;      end;      AStream:=CoStream.Create;      AStream.Open(EmptyParam,adModeUnknown,adOpenStreamUnspecified, ‘‘, ‘‘);      AStream.Type_:=adTypeBinary;      AStream.Write(V);      AR:=_Recordset(CoRecordset.Create);      AStream.Position:=0;      AR.Open(AStream,EmptyParam,adOpenUnspecified, adLockUnspecified, -1);      ADOQuery1.Recordset:=ADOInt._Recordset(AR);    finally      DCOM.Connected:=false;    end; end; //保存资料 procedure TForm1.Button6Click(Sender: TObject); var    AStream:_Stream;    V:OLEVariant; begin    DCOM.Connected:=true;    try      ADOQuery1.CheckBrowseMode;      AStream:=CoStream.Create;      OLEVariant(ADOQuery1.Recordset).Save(AStream,adPersistADTG);      AStream.Position:=0;      V:=AStream.Read(AStream.Size);      DCOM.AppServer.SaveADOData(V);      ADOQuery1.UpdateBatch;   //no connection,means clearchangelog    finally      DCOM.Connected:=false;    end; end;