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<hr><p align="left"><small>发信人: strayli (stray), 信区: Delphi <br>
标 题: A Technical View of Borland MIDAS Part II (6) <br>
发信站: BBS 水木清华站 (Thu Nov 12 22:19:15 1998) WWW-POST <br>
<br>
Error Handling <br>
When working with remote data sets, there are going to be occasions when <br>
errors occur. For instance, if two users are accessing a table at the same <br>
time, then it is possible that they will both want to change the same record. <br>
In this case, the person who first performed the update would succeed in <br>
changing the record, while the second person would get an error. <br>
<br>
Errors are passed back to a TClientDataSet and can be handled by responding <br>
to the OnReconcileErrorEvent. A detailed explanation of responding to errors <br>
would take up almost as many pages as I've written so far, so I will consider <br>
that topic beyond the scope of this paper. However, there is a simple <br>
solution to this whole problem that can be covered in just a few paragraphs. <br>
<br>
<br>
The trick to handling errors returned from an Application Server is to use a <br>
form stored in the Delphi Object Repository. To find the form in question, <br>
select File | New from the menu, turn to the Dialogs page, and opt to Copy <br>
the Reconcile Error Dialog. Save the dialog in the same directory as your <br>
current project, and remove it from the files that are automatically created <br>
at start up. To do this, choose Project | Options | Forms from the Delphi <br>
menu. <br>
<br>
Add the Reconcile Error Dialog to the uses list of the appropriate form in <br>
your project. In many cases, this will be the main form for your project. Now <br>
add the following in response to an OnReconcileError event: <br>
<br>
procedure TForm1.CustomerClientDataSetReconcileError( <br>
<br>
DataSet: TClientDataSet; E: EReconcileError; UpdateKind: TUpdateKind; <br>
<br>
var Action: TReconcileAction); <br>
<br>
begin <br>
<br>
Action:=HandleReconcileError(Dataset, UpdateKind, E); <br>
<br>
end; <br>
<br>
This one line function will launch the dialog you found in the Object <br>
Repository and give the user the ability to handle any errors, as shown in <br>
Figure 5. <br>
Figure 5. <br>
<br>
<br>
<br>
Figure 5: The OnReconcile Error Dialog from the Delphi Object Repository as <br>
it appears at run time. <br>
<br>
The grid in the center of the form tells the name of the field on which the <br>
error occured. The Modified Value is the value the client application wanted <br>
to insert into the record. The Conflicting value is the value the "other guy" <br>
who beat you to the update inserted into the record. The Original Value is <br>
the value the record had before either update was made. As you can see, the <br>
user has the option to Skip, Cancel, Correct, Refresh or Merge the data. <br>
<br>
Needless to say, you can make all these changes, and access all these options <br>
by writing your own code. However, it probably makes more sense just to use <br>
this dialog, or to use the dialog as the basis for your own code. <br>
<br>
That is all I want to say about the process of creating a client or server <br>
application. The rest of this paper will deal with connectivity issues. <br>
Remember that a pair of programs called CustOrdersClient and CustOrdersServer <br>
accompany this paper. If you are having trouble finding these examples, you <br>
can look for them on my web site: users.aol.com/charliecal. <br>
<br>
<br>
<br>
-- <br>
※ 来源:·BBS 水木清华站 bbs.net.tsinghua.edu.cn·[FROM: 202.38.79.111] <br>
</small><hr>
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