谷歌搜索发现许多文章说,如果不关闭并重新打开主 CDS,则使用嵌套的 ClientDataSets 根本不可能,在这种情况下,OP 不想这样做。然而 ...
q 的简短回答是肯定的,在我测试过的相当简单的情况下,它非常简单,如果有点啰嗦;正确采取必要的步骤需要一段时间才能弄清楚。
代码如下,其中包含解释其工作原理和一些潜在问题以及如何避免或解决这些问题的注释。我只用 TAdoQueries 为 CDS 的 Provider 进行了测试。
当我开始研究这一切时,很快就发现,在通常的主 + 明细设置下,虽然 Providers + CDS 很乐意从服务器刷新主数据,但他们一旦完成就不会刷新明细记录自打开 cdsMaster 以来第一次从服务器读取。当然,这可能是设计使然。
我认为我不需要发布 DFM 来使用代码。我只是以通常的主从方式设置了 AdoQueries(详细查询以主服务器的 PK 作为参数),一个 DataSetProvider 指向主 AdoQuery,一个主 CDS 指向提供程序,一个详细 cDS 指向cdsMaster 的 DataSetField。为了试验并查看发生了什么,每个数据集都有 DBGrids 和 DBNavigators。
简而言之,下面代码的工作方式是将 AdoQuery master 和 CDS masterdown 临时过滤到当前行,然后强制刷新它们的数据和当前 master 行的 dtail 数据。这样做,与我尝试过的任何其他方式不同,会导致嵌套在 cdsMaster 的 DataSet 字段中的详细信息行被刷新。
顺便说一句,我尝试过的其他死胡同包括和不设置 poFetchDetailsOnDemand 为真,同上 cdsMaster.FetchDetailsOnDemand。显然“FetchDetailsOnDemand”并不意味着 ReFetchDetailsOnDemand!
我遇到了一个或两个问题,让我的“解决方案”正常工作,这个 SO 问题中描述了最棘手的问题:
刷新嵌套在 DataSetField 中的 ClientDataSet
我已经验证这可以与 Sql Server 2000(!) 后端一起正常工作,包括从 ISqlW 获取在服务器上触发的行数据更改。我还使用 Sql Server 的 Profiler 验证了刷新中的网络流量仅涉及单个主行及其详细信息。
德尔福 7 + Win7 64 位,顺便说一句。
procedure TForm1.cdsMasterRowRefresh(MasterPK : Integer);
begin
// The following operations will cause the cursor on the cdsMaster to scroll
// so we need to check and set a flag to avoid re-entrancy
if DoingRefresh then Exit;
DoingRefresh := True;
try
// Filter the cdsMaster down to the single row which is to be refreshed.
cdsMaster.Filter := MasterPKName + ' = ' + IntToStr(MasterPK);
cdsMaster.Filtered := True;
cdsMaster.Refresh;
Inc(cdsMasterRefreshes); // just a counter to assist debugging
// release the filter
cdsMaster.Filtered := False;
// clearing the filter may cause the cdsMaster cursor to move, so ...
cdsMaster.Locate(MasterPKName, MasterPK, []);
finally
DoingRefresh := False;
end;
end;
procedure TForm1.qMasterRowRefresh(MasterPK : Integer);
begin
try
// First, filter the AdoQuery master down to the cdsMaster current row
qMaster.Filter := MasterPKName + ' = ' + IntToStr(MasterPK);
qMaster.Filtered := True;
// At this point Ado is happy to refresh only the current master row from the server
qMaster.Refresh;
// NOTE:
// The reason for the following operations on the qDetail AdoQuery is that I noticed
// during testing situations where this dataset would not be up-to-date at this point
// in the refreshing operations, so we update it manually. The reason I do it manually
// is that simply calling qDetail's Refresh provoked the Ado "Insufficient key column
// information for updating or refreshing" despite its query not involving a join
// and the underlying table having a PK
qDetail.Parameters.ParamByName(MasterPKName).Value := MasterPK;
qDetail.Close;
qDetail.Open;
// With the master and detail rows now re-read from the server, we can update
// the cdsMaster
cdsMasterRowRefresh(MasterPK);
finally
// Now, we can clear the filter
qMaster.Filtered := False;
qMaster.Locate(MasterPKName, MasterPK, []);
// Obviously, if qMaster were filtered in the first place, we'd need to reinstate that later on
end;
end;
procedure TForm1.RefreshcdsMasterAndDetails;
var
MasterPK : Integer;
begin
if cdsMaster.ChangeCount > 0 then
raise Exception.Create(Format('cdsMaster has %d change(s) pending.', [cdsMaster.ChangeCount]));
MasterPK := cdsMaster.FieldByName(MasterPKName).AsInteger;
cdsDetail.DisableControls;
cdsMaster.DisableControls;
qDetail.DisableControls;
qMaster.DisableControls;
try
try
qMasterRowRefresh(MasterPK);
except
// Add exception handling here according to taste
// I haven't encountered any during debugging/testing so:
raise;
end;
finally
qMaster.EnableControls;
qDetail.EnableControls;
cdsMaster.EnableControls;
cdsDetail.EnableControls;
end;
end;
procedure TForm1.cdsMasterAfterScroll(DataSet: TDataSet);
begin
RefreshcdsMasterAndDetails;
end;
procedure TForm1.cdsMasterAfterPost(DataSet: TDataSet);
// NOTE: The reason that this, in addition to cdsMasterAfterScroll, calls RefreshcdsMasterAndDetails is
// because RefreshcdsMasterAndDetails only refreshes the master + detail AdoQueries for the current
// cdsMaster row. Therefore in the case where the current cdsMaster row or its detail(s)
// have been updated, this row needs the refresh treatment before we leave it.
begin
cdsMaster.ApplyUpdates(-1);
RefreshcdsMasterAndDetails;
end;
procedure TForm1.btnRefreshClick(Sender: TObject);
begin
RefreshcdsMasterAndDetails;
end;
procedure TForm1.cdsDetailAfterPost(DataSet: TDataSet);
begin
cdsMaster.ApplyUpdates(-1);
end;