Ive spent the better part of the last two years doing nothing but K2 workflow development, which until very recently could only be done in Visual Studio 2005 so I am a bit behind the times. I seem to have skipped over using Visual Studio 2008 entirely, and I am now ready to stumble through all that Ive missed. Not that I will abandon my K2 ramblings, but I need to get back to some of the other technologies I am passionate about but havent had the option of working with them on a day-to-day basis as I have with K2 blackpearl. Specifically, I am going to be focusing my efforts on what is new in the Entity Framework and WPF in Visual Studio 2010, though you have to keep in mind that since I have skipped VS 2008, I may be giving VS 2010 credit for things that really have been around for a while (hey, if I havent seen it, it is new to me!). I have the following simple goals in mind for this exercise: Entity Framework
Model an inherited class Entity Framework
Model a lookup entity WPF Bind a list of entities WPF - on selection of an entity in the bound list, display values of the selected entity WPF For the lookup field, provide a dropdown of potential values to lookup All of these goals must be accomplished using as little code as possible, relying on the features we get out of the box in Visual Studio 2010. This isnt going to be rocket science here, Im not even looking to get or save this data from/to a data source, but I gotta start somewhere and hopefully it will grow into something more interesting. For this exercise, I am going to try to
model some fictional data about football players and personnel (maybe turning this into some sort of NFL simulation game if I lose my job and can play with this all day), so Ill start with a Person class that has a name property, and extend that with a Player class to include a Position lookup property. The idea is that a Person can be a Player, Coach or whatever other personnel type may be associated with a football team but well only flesh out the Player aspect of a person for this. So to get started, I fired up Visual Studio 2010 and created a new WPF Application: To this project, I added a new ADO.NET Entity Data
Model named PlayerModel (for now, not sure what will be an appropriate name so this may be revisited): I chose for it to be an empty
model, as I dont have a database designed for this yet: Using the toolbox, I dragged out an entity for each of the items we identified earlier: Person, Player and Position, and gave them some simple properties (note that I kept the default Id property for each of them): Now to figure out how to link these things together the way I want to first, lets try to tell it that Player extends Person. I see that Inheritance is one of the items in the toolbox, but I cant seem to drag it out anywhere onto the canvas. However, when I right-click an element, I get the option to Add Inheritance to it, which gives us exactly what we want: Ok, now that we have that, how do we tell it that each player has a position? Well, despite association being in the toolbox, I have learned that you cant just drag and drop those elements so I right click Player and select Add -> Association to get the following dialog: I see the option here to Add foreign key properties to my entities Ive read somewhere this this is a new and highly-sought after feature so Ill see what it does. Selecting it includes a PositionId on the Player element for me, which seems pretty database-centric and I would like to see if I can live without it for now given that we also got the Position property out of this association. Ill bring it back into the fold if it ends up being useful later. Here is what we end up with now: Trying to compile this resulted in an error stating that the Player entity cannot have an Id, because the Person element it extends already has a property named Id. Makes sense, so I remove it and compile again. Success, but with a warning but success is a good thing so Ill pretend I didnt see that warning for now. It probably has to do with the fact that my Player entity is now pretty useless as it doesnt have any non-navigation properties. So things seem to match what we are going for, great now what the heck do we do with this? Lets switch gears and see what we get for free dealing with this
model from the UI. Lets open up the MainWindow.xaml and see if we can connect to our entities as a data source. Hey, whats this? Have you read my mind, Visual Studio? Our entities are already listed in the Data Sources panel: I do notice, however, that our Player entity is missing. Is this due to that compilation warning? Ill add a bogus property to our player entity just to see if that is the case no, still no love. The warning reads: Error 2062: No
mapping specified for instances of the EntitySet and AssociationSet in the EntityContainer PlayerModelContainer. Well if everything worked without any issues, then I wouldnt be stumbling through at all, so lets get to the bottom of this. My good friend google indicates that the warning is due to the
model not being tied up to a database. Hmmm, so why dont Players show up in my data sources? A little bit of drill-down shows that they are, in fact, exposed under Positions: Well now that isnt quite what I want. While you could get to players through a position, it shouldnt be that way exclusively. Oh well, I can ignore that for now lets drag Players out onto the canvas after selecting List from the dropdown: Hey, what the heck? I wanted a list not a listview. Get rid of that list view that was just dropped, drop in a listbox and then drop the Players entity into it. That will bind it for us. Of course, there isnt any data to show, which brings us to the really hacky part of all this and that is to stuff some test data into our view source without actually getting it from any data source. To do this through code, we need to grab a reference to the positionsPlayersViewSource resource that was created for us when we dragged out our Players entity. We then set the source of that reference equal to a populated list of Players. Well add a couple of players that way as well as a few positions via the positionsViewSource resource, and Ill ensure that each player has a position specified. Ultimately, the code looks like this: System.Windows.Data.CollectionViewSource positionViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("positionsViewSource"))); List<Position> positions = new List<Position>(); Position newPosition = new Position(); newPosition.Id = 0; newPosition.Name = "WR"; positions.Add(newPosition); newPosition = new Position(); newPosition.Id = 1; newPosition.Name = "RB"; positions.Add(newPosition); newPosition = new Position(); newPosition.Id = 2; newPosition.Name = "QB"; positions.Add(newPosition); positionViewSource.Source = positions; System.Windows.Data.CollectionViewSource playerViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("positionsPlayersViewSource"))); List<Player> players = new List<Player>(); Player newPlayer = new Player(); newPlayer.Id = 0; newPlayer.Name = "Test Dude"; newPlayer.Position = positions[0]; players.Add(newPlayer); newPlayer = new Player(); newPlayer.Id = 1; newPlayer.Name = "Test Dude II"; newPlayer.Position = positions[1]; players.Add(newPlayer); newPlayer = new Player(); newPlayer.Id = 2; newPlayer.Name = "Test Dude III"; newPlayer.Position = positions[2]; players.Add(newPlayer); playerViewSource.Source = players; Now that our views are being loaded with data, we can go about tying things together visually. Drop a text box (to show the selected players name) and a combo box (to show the selected players position). Drag the Positions entity from the data sources panel to the combo box to wire it up to the positions view source. Click the text box that was dragged, and find its Text property in the properties pane. There is a little glyph next to it that displays Advanced Properties when hovered over click this and then select Apply Data Binding. In the dialog that appears, we can select the current players name as the value to bind to: Similarly, we can wire up the combo boxs SelectedItem value to the current players position: When the application is executed and we navigate through the various players, we automatically get their name and position bound to the appropriate fields: All of this was accomplished with no code save for loading the test data, and I might add, it was pretty intuitive to do so via the drag and drop of entities straight from the data sources panel. So maybe all of this was old hat to you, but I was very impressed with this experience and I look forward to stumbling through the caveats of doing more complex data modeling and binding in this fashion. Next up, I suppose, will be figuring out how to get the entities to get real data from a data source instead of stuffing it with test data as well as trying to figure out why Players ended up being under Positions in the data sources panel.Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.
