Does anybody know the logic behind making DataSourceSelectArguments sealed?
I've implemented a custom DataSource (and related classes) for some custom business objects and custom WebControls. When thinking in filters (like in a grid) I discovered that the DataSourceSelectArguments is sealed. Surely, I'm missing something. (Maybe the logic is related to the fact that is nonsense to ask the DB again, just for filtering?, just a guess.)
My guess is because the class is a dumb data transfer object merely used to pass arguments to a method.
This class itself doesn't have any operations defined on it, thus what sort of polymorphism would you expect? For example, the existing methods will only know about the properties of this class, which are all settable, so there's no need to override the properties. If you added new properties, they would get ignored.
For your own method, can you create your own Arguments class that just happens to have all the same properties?
Sorry for the delay, I was on holydays. :)
The problem is that a DataBoundControl such as ListView has a SortExpression property, but not a FilterExpression. It is fine to implement a sortable grid/list with a ListView by means of a IButtonControl WebControl that fires a PostBack and a Command event. Then you use the SortExpression or the Sort method and pass a sort expression that will fill the DataSourceSelectArguments.SortExpression and pass it to the DataSource which can construct the apropiate SQL statement (in my case) to retrieve the Data from the DB. This allows for separation between the Data and the WebControl that displays it, IMHO.
Following this pattern I was about to implement a filter by filling an extra parameter object in my DataSourceSelectArguments with the requested filter and I will have called Sort, which would have passed this arguments object to the DataSource, where I would have constructed the appropiate select clause.
I've finally solve it by "coding" the filter information in the SortExpression, but I find it ugly (for the name, in the first place: sort != filter), and I was wondering if there's a more appropiate way of doing this or if I'm missing something that is more subtle.
Edit:
Maybe a better approach would be to override ListView's PerformSelect method and ask my own implementation of the DataSourceView if it can filter, then call a special ExecuteSelect method that accepts a special DataSourceSelectArguments with a filter object. Taking care not to do anything that will break when someone use the custom ListView with a non-enhanced DataSourceView, of course.