How does one do MVC2/EF4 EntityCollection validation w/ data annotations? - validation

Question

I have finally gotten over one hurdle and can now successfully create new model data. Now there's another catch - validation. Most of the validation seems easy enough as a lot of my model data are scalar values. There is a many-to-many relationship I link to, however, so I'm not sure how to go about validating that. My model is (once again):
Game (only listing the relevant columns):
GameID - int (primary key, auto-incr)
Platform:
PlatformID - int (primary key, auto-incr)
Name - string
GamePlatform (not a visible entity):
GameID - int (foreign key from Games)
PlatformID - int (foreign key from Platforms)
And my Create method (yes, I know it's sloppy and amateurish - I am an amateur and trying to learn. I'll definitely add error checking to it. I'm just trying to get the big picture of the view->controller->validation->persist-in-db/show errors process down):
public ActionResult CreateReview([Bind(prefix = "GameData")]Game newGame, int[] PlatformIDs)
{
try
{
foreach(int i in PlatformIDs)
{
Platform plat = _siteDB.Platforms.Single(p => p.PlatformID == i);
newGame.Platforms.Add(plat);
}
newGame.LastModified = Datetime.Now;
_siteDB.Games.AddObject(newGame);
_siteDB.SaveChanges();
return RedirectToAction("Index");
}
catch
{
return View();
}
}
The array of PlatformIDs are supplied by a group of checkboxes within my view. For my Game to be valid, it must be associated with at least one Platform. I'm just not sure how to validate that with data annotations, or if it's even possible to do so. Any help would be greatly appreciated.

Answer 1

If I understand your question correctly, your int[] potentially contains ints associated with the ID of a Platform in your DB and you want to make sure your int[] contains at least one valid PlatformID, correct?
Immediately you could do just a simple check prior to going into your logic:
// If there aren't any IDs in Platform that are in PlatformIDs...
if (!_siteDB.Platforms.Any(p => PlatformIDs.Contains(p.PlatformID)))
Return RedirectToAction("Index");
// And probably tell the user to check a box, if they did,
// One of your checkboxes isn't matching up with your PlatformIDs
Ideally what you'd want to do is add the int[] to your model so you can check model validation. Since databased don't typically store int[], add it to your Game model. The EF probably put your DB Entities in your Models folder and if you look at them, you'll see they're partial classes. So add this in your Models folder:
public partial class Game
{
public Dictionary<int, bool> SupportedPlatforms { get; set; }// Edited
}
// Also add this which you'll see why below
public partial class Platform
{
public static bool IsValidPlatformID(int PlatformID)
{
using (SiteDBEntities _siteDB = new SiteDBEntities())
return _siteDB.Platforms.Any(p => p.PlatformID.Equals(PlatformID));
}
}
Then add a custom ValidationAttribute class:
public ContainsValidPlatformIDAttribute : ValidationAttribute
{
public ContainsValidPlatformIDAttribute() { }
public override bool IsValid(object value)
{
Dictionary<int, bool> supportedPlatforms = (Dictionary<int, bool>)value;
if (value == null)
return true;
foreach (int i in values)
{
if (supportedPlatforms.Values.Any(b => b.Equals(true)))// Edited
return false;
}
return true;
}
Now decorate your Property with it in the Game class:
[ContainsValidPlatformID(Error = "You did not select a valid Platform.")]
public Dictionary<int, bool> SupportedPlatforms { get; set; }// Edited
(Edited)Now instead of hard coding a checkbox for each platform, add this instead:
<%: Html.CheckboxFor(model => model.SupportedPlatforms[0]) %>
<%: Html.ValidationMessageFor(model => model.SupportedPlatforms[0]) %>
(Edited)Now your checkboxes are tied to the Model, you can validate the model in the controller, and you can remove the int[] argument from your Action method. This has all been coded from my head into this editor so you may need to tweak some things here and there but this is the direction you should be heading in when working with Models in Views.
Also, check out what Scott Guthrie has written on the topic of MVC Model Validation in his blog. Hopefully with my sample and Scott's blog, you'll be pointed in the right direction.