Hi,

I'm developing a site that uses this book as a basis for separating the different layers.

I have a page with an ObjectDatasource and a Gridview connected to it using proper BLL and DAL classes to update rows in the database. Now, every time I do an update I want to display a message to the user using a label. By using the gridview's RowUpdated action in the code-behind file, I can get the number of rows affected by using e.AffectedRows (if it was working properly).

It will always return "Oooops", but the database is still updated. Why isn't this working?


Another thing, assuming that this is working: would this be proper separation of the layers, or should I set the label's text in the BLL? If so, how can one do that?

I'd guess you'll get an exception if an update doesn't work. I wouldn't go out of my way to test myself. Just make sure you have page level and global error handlers set up.

You must never set the value of any UI element in the BLL or DAL layers! That breaks the fundamental reason for having a separation of tiers.

Eric

hmm... ok.

But how can the UI know what error message to output? Say that I have an image that is connected to a page in a database. If I try to delete the image from the database, the UI should say (something like this): "Error: image cannot be deleted because it is in use on a page."

A solution for this is to have a custom made link button and from that's onclick method try call the BO calling the DAL. The problem is that by doing this I lose the connection that the datagrid, or a formview, and the objectdatasource has, meaning that I have to use the FindControl() method to find every control, get the value/text from each control, and from that create an object to send to the BO and DAL. It is a lot of work....

Is there a way to get the messages from the BLL to the UI without doing this?

"But how can the UI know what error message to output?"

If you use ("try" and throw exception) on your DAL you can see what error you receive!

But remember to log this error and don't show it to user is visiting your page.

If you want to made an update, use your DAL to return True if update was made, and False case else... (Don't forget throw exception)
The BLL continue to retrieve True or false from the DAL and send it to the UI.

If BLL send true to the UI you set lblFeedback.Text = "Row updated";
If BLL send false to the UI you set lblFeedback.Text = "Ooops";

If any error occur in BLL or DAL like ("image is in use, can´t find table, can't find database, etc) it is automatically shown (if you do the right "throw exception everywhere this type of error may occur)