ADOQuery代替ClientDataSet做3Tier系统

ADOQuery代替ClientDataSet做3-Tier系统

2005-09-06 13:41:00

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;