C / C++ / MFC

17-Dec-08 8:11

Hi,

I'm fairly new to database programming, but I have been using MFC and C++ for a while. So, here is the problem I'm having.

Here is a basic description of the two tables I'm using.
PersonTable
PersonId, INT, AUTO_INCREMENT (Primary Key)
Name, VARCHAR(32)

ImageTable
ImageId, INT, AUTO_INCREMENT (Primary Key)
ImageBlob, LARGE_BLOB
PersonId, INT (Foreign Key)

Basically, I want to insert the person record into the person table, next insert the image for that person into the image table, and finally link the ImageTable.PersonId to the PersonTable.PersonId.

So, here is the code I'm currently using

<br />
personTable.AddNew();<br />
personTable.m_Name = "Joe";<br />
personTable.Update();<br />
<br />
personTable.Requery();<br />
personTable.MoveLast();<br />
<br />
long personId_ForeignKey = personTable.m_PersonId;<br />
<br />
//... later in the image table insert code<br />
imageTable.AddNew();<br />
// set the image blob here<br />
imageTable.m_PersonId = personId_ForeignKey;<br />
imageTable.Update();

This works, but what concerns me is that this isn't safe for concurrent inserts. If multiple clients are inserting into the database, then I could get the wrong foreign key when I call "personTable.MoveLast()." Is there a better way to do this? Thanks!

-Will

led mike17-Dec-08 9:13

led mike

17-Dec-08 9:13

mevatron1 wrote:
Is there a better way to do this?

Yes, several, for example Stored Procedures[^]

led mike

mevatron117-Dec-08 11:16

17-Dec-08 11:16

Do you have an example of a stored procedure to do that for my simple tables? Will the imageBlob be a problem for the stored procedure?

-Will

led mike18-Dec-08 6:53

led mike

18-Dec-08 6:53

mevatron1 wrote:
Do you have an example of a stored procedure to do that for my simple tables?

Will, I also saw your reply to David. While there might be an example identical to your scenario I am not aware of one. That said there is certainly much information about stored procedures. They can be product specific so make sure you use the documentation and tutorials for the database product you are working with. Also there is a Database forum here at code project.

I strongly urge you to take some time learning about database programming. Like most subjects in software development, there are choices that come with benefits and detractors and not knowing the details of the subject (database development ) can lead to undesirable results.

led mike

mevatron118-Dec-08 7:17

18-Dec-08 7:17

Mike, Thank you very much for your advice. I will definitely continue to look into stored procedures to try to learn how to solve this problem.

-Will

David Crow17-Dec-08 10:30

David Crow

17-Dec-08 10:30

What about wrapping the code in a transaction, like:

personTable.m_pDatabase->BeginTrans();
 
personTable.AddNew();
personTable.m_Name = "Joe";
personTable.Update();
 
personTable.Requery();
personTable.MoveLast();
 
personTable.m_pDatabase->CommitTrans();

I'm not sure if it's optimal, however.

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

mevatron117-Dec-08 11:16

17-Dec-08 11:16

I can certainly give this a try! Thanks for the reply!

-Will

mevatron117-Dec-08 11:48

17-Dec-08 11:48

Sadly, this doesn't work.

I set a breakpoint on the personTable.Requery() line

personTable.m_pDatabase->BeginTrans();
 
personTable.AddNew();
personTable.m_Name = "Joe";
personTable.Update(); // <-- This inserts a new key == 1
 
personTable.Requery(); // <-- placed breakpoint here
personTable.MoveLast();
 
personTable.m_pDatabase->CommitTrans();

I then ran another instance of the program to let it run to completion first, so I ended up with the imageTable.PersonId == 2 for both rows in the imageTable. Thanks for your time!

-Will

About USB ports

ameyakoshti17-Dec-08 7:09

ameyakoshti

17-Dec-08 7:09

Few months back i had asked about how to disable USB ports thru vc++.
and i got replies saying disable it through registry.

one thing i forgot to ask.

if i disable the USB post through registry then will windows still recognise the USB ports??
and will it still send some power to it?
and is there any way to control the power to it?

basically m making a project on power management.
can someone help me out with it?

i need help on accessing BIOS from windows...

Jonathan Davies17-Dec-08 7:33

Jonathan Davies

17-Dec-08 7:33

Hi,
Have a look at: http://msdn.microsoft.com/en-us/library/ms791235.aspx This is part of the setup api which I recently used to find the names of devices (such as usb ports). The documentation on this method mentions enabling/disabling. It seems cleaner to use these methods rather than access the registry directly. Have a look at http://www.codeproject.com/KB/wtl/DeviceInformation.aspx which is code I used to see the devices and might help. It does need WTL to compile though.

ameyakoshti17-Dec-08 8:09

ameyakoshti

17-Dec-08 8:09

hey i jus saw the article

but this is want i dont like:
"DICS_DISABLE
Disables the device. If the device can be disabled but this function cannot disable the device dynamically, this function marks the device to be disabled the next time the machine reboots. "

i need to disable the USB port thru my prog and then enable it again without restarting the comp.

Jonathan Davies18-Dec-08 2:07

Jonathan Davies

18-Dec-08 2:07

Hi,

I'd expect power saving to be apply to most devices, not just USB, so it's quite possible there is an API to do this. Just as the setup API I mentioned provided what I needed. In a quick search on MSDN I found http://msdn.microsoft.com/en-us/library/aa387973(VS.85).aspx. This starts off: "The CIM_PowerSupply class represents the capabilities and management of the power supply logical device.". I don't know if this applies to USB but this could be where you need to start researching.