Make a change to an application that uses the Data Access Layer technique

I think I like this technique in general. I have to admit that the learning curve was high. But once you got used to, I think you would become liking it. Especially if you are a guy like me, who had an ASP doing everying. No “three tier”… but who on the other hand, like OO (object oriented) programming.

As always with a tool like this, a RAD, it is less complicated when you create a brand-new app. But today, I need to add some new fields to the DetailView, to the database table behind.

Of course, you first add the column to the database table.

Then with the TableAdapter representing the table, you should first adapt the main select query. You should not add the column to the DataTable yourself. VS does that for you.

When the change is saved, VS asks you whether you want the update command too adapted. You may find it useful, if you do not do anything special with the update statement, but if you do, ATTENTION, with this auto adaptation, your manual editing of the update statement will be all gone. By the way, it apapts the insert command too, when you say YES.

I had the following difficulty.
As said, I added some new columns to an existing table. One of them was a BOOLEAN field. A bit column in SQL.
I added a CheckBox to the DetailedView for it, and got error saying unable to convert DBNull to BOOLEAN.

OK. Understand. For all existing data it is NULL because I created the column to accept NULL... wait a minute… I could have set the default value…
Anyway, I made it work by setting it to FALSE in the DAL class. First get data in the DataTable calling a GET method of the TableAdapter, then set the field to FALSE if the original value is NULL.