Subsonic: Bring me to tiers

Question

Hi guys,

This is an embarrassingly basic n-tier question.

I've created a DAL project in VS2008 with subsonic. It's got a widget class, a widgetcollection class, and a widgetcontroller class.

I've created my Business logic project (no I can't put it in the same tier) that references it. Using certain business criteria, it selects a collection of widgets in a function that returns a widgetcollection.

My question is: how does my GUI layer bind the collection to a grid? I know that the widgetcollection is a valid datasource for a datagrid, but how does the GUI layer know what a widget and widgetcollection are? Surely I don't have to reference the DAL from the GUI, that negates the whole point.

Answer 1

(using SubSonic 2.x) In my BLL classes I have a property which gives an object reference to the relevant DAL class. My UI form has a reference to the BLL class, so from the form I can address the DAL properties and methods via .BLL.DAL.xxxx

FWIW, I have never managed to successfully bind a SubSonic collection to a DataGridView. As alternatives, I sometimes use the collections .ToTable() method to create a DataTable and then bind to that, or alternatively I manually bind using .AddRow()

Answer 2

Look at the documentation for IBindingList Interface in MSDN, it has a pretty good sample. Create, for example, a CustomersList class in your model that uses a Customer class in your BLL. Bind the grid to an instance of the CustomersList class. The presentation layer has no knowledge of the subsonic table classes.

Answer 3

You probably need to use an Interface. You can easily create an interface based off of the Widget in your Dal(right click on the class and create an Interface from the class). Next take the Interface and add it to your Business Logic Layer or a seperate project just for interfaces. Once you have done that you can add a reference to the Interface both in the DAL and in the GUI. This can also help if you ever change your data storage from a Database to XML etc. etc.

Answer 4

Firstly, I dont think this is an embarrasingly basic n-tier question. It is a very interesting subject and one I attempted to stimulate discussion for in the old Subsonic Forums.

I share your reluctance to expose my GUI layer to the DAL.

My GUI layer only talks to BLL using the vocabulary and topics of my own Entity Model and only returns my own entities or lists or in some cases Data Tables.

My BLL only talks to a MAPping layer which maps Fetches,Saves etc to the appropriate DAL CRUD methods and converts the returned Subsonic types to my Entity types.

In doing this I was suprised at how much of Subsonic I had to duplicate and at times I felt I was going down the wrong road, I am feeling more comfortable with it now, though it still needs refactoring and refining.

For example, finding a flexible, generic means of indicating to my BLL which row(s) I wanted returned in a fetch was a challenge I hadn't expected and I finished up writing a generic queryClass with fluent interface which looks a lot like a Subsonic Select.

FWIW, I think you are headed down the right track, I guess what you have to do though is decide how you want to define those Subsonic types to your GUI.

Rob has an interesting discussion you may be interested in.