Solved

Multi Threading

Posted on 2002-04-02
5
338 Views
Last Modified: 2010-04-04
I am creating a multi user MDI application.

I have created datamodules for database connection.

when i open two instance of same screen they show me the same record because they are reffering to the same recordset.

What shall i do to have different instanse of database connection for different instance of MDI child screens.

Regards

Mahesh
0
Comment
Question by:princemahesh
5 Comments
 
LVL 2

Expert Comment

by:isstorr
Comment Utility
If you use a TADOTable for instance on a datamodule, you will get a common connection. Instead try creating your database components on the fly at runtime for each MDI instance -

type
  TMyMDIClass = class(TForm);
  private
   FTable: TADOTable
  public
  constructor Create; override;
  destructor Destroy;
  end;

constructor Create;
begin
 inherited;
 FTable := TADOTable.Create(self);
.
.
.
end;

destructor Destroy;
begin
 FTable.Free;
 inherited;
end;

You can use a common ADOConnection (though you can also give each instance its own connection as well if you wish) but this will ensure that each instance has its own dataset.

Si
0
 
LVL 10

Expert Comment

by:Jacco
Comment Utility
Hi there,

The way I see it you need a DataModule for the database connection (with the TSession and TDataBase components) call it datMainConnection. And for every MDI Instance you can create a separate datamodule with DataSets on it which you connect to the TDataBase on the datMainConnection. This way you'll have one set of DataSets per MDI.

DataSources should go on the MDI Child itself. And you have to connect the datasources to the DataSets on the datMDIdata manually (for example in the FormCreate or the constructor).

When I use this technique I always have the datMDIdata created in the constructor of the MDIChild and store it in a private field.

This way you only have one TDataBase component (not wasting connection licenses and resources).

Regards Jacco
0
 
LVL 2

Accepted Solution

by:
isstorr earned 50 total points
Comment Utility
BDE TTable/TDataSet equivalent of my earlier post -

type
 TMyMDIClass = class(TForm); // TDataModule or even TComponent if you prefer.
 private
  FTable: TTable;
  FDataSource: TDataSource;
 public
 constructor Create; override;
 destructor Destroy;
 end;

constructor Create;
begin
inherited;
FTable := TTable.Create(self);
FDataSource := TDataSource.Create(self);
FDataSource.DataSet := FTable;
.
.
.
end;

destructor Destroy;
begin
FDataSource.Free;
FTable.Free;
inherited;
end;
0
 
LVL 1

Expert Comment

by:Moondancer
Comment Utility
ADMINISTRATION WILL BE CONTACTING YOU SHORTLY.  Moderators Computer101 or Netminder will return to finalize these if they are still open in 14 days.  Experts, please post closing recommendations before that time.

Below are your open questions as of today.  Questions which have been inactive for 21 days or longer are considered to be abandoned and for those, your options are:
1. Accept a Comment As Answer (use the button next to the Expert's name).
2. Close the question if the information was not useful to you, but may help others. You must tell the participants why you wish to do this, and allow for Expert response.  This choice will include a refund to you, and will move this question to our PAQ (Previously Asked Question) database.  If you found information outside this question thread, please add it.
3. Ask Community Support to help split points between participating experts, or just comment here with details and we'll respond with the process.
4. Delete the question (if it has no potential value for others).
   --> Post comments for expert of your intention to delete and why
   --> YOU CANNOT DELETE A QUESTION with comments; special handling by a Moderator is required.

For special handling needs, please post a zero point question in the link below and include the URL (question QID/link) that it regards with details.
http://www.experts-exchange.com/jsp/qList.jsp?ta=commspt
 
Please click this link for Help Desk, Guidelines/Member Agreement and the Question/Answer process.  http://www.experts-exchange.com/jsp/cmtyHelpDesk.jsp

Click you Member Profile to view your question history and please keep them updated. If you are a KnowledgePro user, use the Power Search option to find them.  

Questions which are LOCKED with a Proposed Answer but do not help you, should be rejected with comments added.  When you grade the question less than an A, please comment as to why.  This helps all involved, as well as others who may access this item in the future.  PLEASE DO NOT AWARD POINTS TO ME.

To view your open questions, please click the following link(s) and keep them all current with updates.
http://www.experts-exchange.com/questions/Q.20178810.html
http://www.experts-exchange.com/questions/Q.20246239.html
http://www.experts-exchange.com/questions/Q.20255268.html
http://www.experts-exchange.com/questions/Q.20255242.html
http://www.experts-exchange.com/questions/Q.20269488.html
http://www.experts-exchange.com/questions/Q.20281446.html
http://www.experts-exchange.com/questions/Q.20283934.html

To view your locked questions, please click the following link(s) and evaluate the proposed answer.
http://www.experts-exchange.com/questions/Q.20145081.html
http://www.experts-exchange.com/questions/Q.20246789.html
http://www.experts-exchange.com/questions/Q.20281038.html

*****  E X P E R T S    P L E A S E  ******  Leave your closing recommendations.
If you are interested in the cleanup effort, please click this link
http://www.experts-exchange.com/jsp/qManageQuestion.jsp?ta=commspt&qid=20274643
POINTS FOR EXPERTS awaiting comments are listed in the link below
http://www.experts-exchange.com/commspt/Q.20277028.html
 
Moderators will finalize this question if in @14 days Asker has not responded.  This will be moved to the PAQ (Previously Asked Questions) at zero points, deleted or awarded.
 
Thanks everyone.
Moondancer
Moderator @ Experts Exchange
0
 
LVL 1

Expert Comment

by:pnh73
Comment Utility
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:

Accept Answer from isstorr

Please leave any comments here within the next seven days.
 
PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!
 
Paul (pnh73)
EE Cleanup Volunteer
0

Featured Post

How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

Join & Write a Comment

Introduction I have seen many questions in this Delphi topic area where queries in threads are needed or suggested. I know bumped into a similar need. This article will address some of the concepts when dealing with a multithreaded delphi database…
Introduction Raise your hands if you were as upset with FireMonkey as I was when I discovered that there was no TListview.  I use TListView in almost all of my applications I've written, and I was not going to compromise by resorting to TStringGrid…
Excel styles will make formatting consistent and let you apply and change formatting faster. In this tutorial, you'll learn how to use Excel's built-in styles, how to modify styles, and how to create your own. You'll also learn how to use your custo…
When you create an app prototype with Adobe XD, you can insert system screens -- sharing or Control Center, for example -- with just a few clicks. This video shows you how. You can take the full course on Experts Exchange at http://bit.ly/XDcourse.

743 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

16 Experts available now in Live!

Get 1:1 Help Now