C# Where to place code that retrieves GUI data?

Question

I'm puzzling with where to place some code. I have a listbox and the listitems are stored in the database. The thing is, where should I place the code that retrieves the data from the database? I do already have a database class with a method ExecuteSelectQuery(). Shall I create Utility class with a method public DataTable GetGroupData() ? /* group is the listbox */ This method then calls the method ExecuteSelectQuery() from the database class.

What should I do?

Answer 1

You could simply abstract the database code into a utility class, as you suggest, and this wouldn't be a terrible solution. (You probably can't get much better with WebForms.) Yet if the system is going to end up quite complicated, then you might want to pick a more formal architecture...

Probably the best option for ASP.NET is the ASP.NET MVC Framework, which fully replaces WebForms. It's built around the Model-View-Controller architecture pattern, which is designed specifically to clearly separate code for the user interface and backened logic, which seems to be exactly what you want. (Indeed, it makes the design of websites a lot more structured in many ways.)

Also, if you want to create a more structured model for your database system, consider using an ORM such as the ADO.NET Entity Framework. However, this may be overkill if your database isn't very complicated. Using the MVC pattern is probably going to make a lot more difference.

Answer 2

Hi,

consider adding a layer between your UI and data access layers. There you can implement some kind of caching if the data is not being changed frequently - this way you will avoid retrieving multiple times the same data from the DB.

I would recommend you the Application Architecture Guide book.

Pavel

Answer 3

There are many data access patterns you could look at implementing. A Repository pattern might get you where you need to go.

The idea is to have a GroupRepository class that fetches Group data. It doesn't have to be overly complicated. A simple method like GetAllGroups could return a collection you can use for your ListBox items.

Answer 4

Looks like you already have the data access layer implemented via your database class. I guess the confusion right now is in implementing the presentation and business layers. To me 'GetGroupData' is more of a part of the Business layer and is the right thing to implement. It will allow you to make changes in future with minimal or no impact to the presentation layer. Therefore, the flow that you suggested looks right. LoadListBox followed by GetGroupData followed by ExecuteSelectQuery.