I'm new in MVC2 and Entity Framework and I tried get a list of products with the respective category name, but it's returned me the error
"Object reference not set to an instance of an object."
I have a table Product with a foreign key Category.
I'm using MVC2 and Entity Framework 4.0.
public class Repository
{
public IQueryable<Produto> ListAllProducts()
{
return entities.Produtos;
}
}
public class AdminProdutoController : Controller
{
TudoDeMassinhaRepository repository = new TudoDeMassinhaRepository();
public ActionResult Index()
{
var produtos = repository.ListAllProducts().ToList();
return View(produtos);
}
}
code in view where the error is generated: <%: item.CatProduto.cat_produto_nome%>
You're only selecting the products - you're not currently including the categories. This means: you'll get back your product objects, but any related objects they refer to are not loaded automatically - that's why the .CatProduto property will be NULL and thus you're getting the error.
You need to explicitly specify which additional entities you want to have loaded - something like:
public IQueryable<Produto> ListAllProductsWithCategories()
{
return entities.Produtos.Include("CatProduto");
}
This way, you should get back your Produto objects, and their CatProduto property should have been loaded and populated, too.
So if you change your index method to be:
public ActionResult Index()
{
var produtos = repository.ListAllProductsWithCategories().ToList();
return View(produtos);
}
it should work.
Related
I use asp.net mvc 5 and EF 6 .I have following code in my controller
var resultOne = stats.GetPlayerStatsByParam(year, modeOne); //first
ViewData["more"] = stats.GetTeamStatsID(year); //second
return View("StatsNew", resultOne.ToList());
I am able to display result in view using "resultOne". Now I want to pass another data to same view using ViewData[]. its a stored procedure and the result is paasing to "ViewData["more"]".
I have done following code for "ViewData["more"]" in View page
But I am getting an error saying that 'object reference not set'
#foreach (var item in ViewData["more"] as #List<demo.GetTeamStatsID_Result>)
{
#item.Pld;
}
Use a viewmodel and extend it by the data coming from stats.GetTeamStatsID(year);
Do not use ViewBag or ViewData if not necessary for some reason (which I can´t imagine right now)
As the comments have already pointed out, build a ViewModel class, that wraps everthing you need:
//I am using fake types here, sinceI don't know your model classes
//substitute accordingly!
public class MyViewModel
{
public PlayerStatsType PlayerStats { get; set;}
public List<demo.GetTeamStatsID_Result> Teams { get; set;}
}
Then in your action method:
var vm = new MyViewModel();
vm.PlayerStats = stats.GetPlayerStatsByParam(year, modeOne); //first
vm.TeamId = stats.GetTeamStatsID(year); //second
return View("StatsNew", vm);
Amend the model declaration in your view:
#model Namespace.Models.MyViewModel //again use namespace for your vm class
Now you can access both properties from your model:
#foreach (var item in Model.Teams)
{
#item.Pld;
}
I'm currently developing a Web API and I'm figuring out about how to add a new method inside my controller FilmsController which has to execute a LINQ query simply returning the related JSON to the user. Everything seems correct but when I try to call that API an error 404 appears. The API I'm trying to call is api/NewFilms, which should be correct.
Here is the method GetNewFilms inside FilmsController:
public IQueryable<Film> GetNewFilms()
{
var query = from f in db.Films
orderby f.ReleaseYear descending
select f;
return query;
}
// GET: api/Films
public IQueryable<Film> GetFilms()
{
return db.Films;
}
With the default routing configuration, web api controller allows to have only one GET action (without any parameters). If you have more than one GET actions, you will get a 500 error with message like
Multiple actions were found that match the request
If you need to have more than one GET actions, you may explicitly define a route pattern for those using Attribute routing.
public class FilmsController : ApiController
{
[Route("api/Films/NewFilms")]
public IEnumerable<string> GetNewFilms()
{
return new List<string> { "New Film 1","New Film 1"};
}
// GET: api/Films
public IEnumerable<string> GetFilms()
{
return new List<string> { "Film 1","Film 2"};
}
public string GetFilm(int id)
{
return "A single film";
}
}
Also, you may consider changing your return type from IQueryable to IEnumerable of your Dto ( instead of the entity class created by your ORM)
There is a field in our database which really ought to be a boolean, but for some reason the original developers made it a CHAR which will either be set to "1" or "0".
[Column("CHARGEABLE")]
[StringLength(1)]
private string Chargeable { get; set; }
I want my model to represent this field as a boolean so I figured I could add a property to my model to wrap it:
[NotMapped]
public bool ChargeableTrue
{
get
{
return Chargeable == "1" ? true : false;
}
set
{
Chargeable = value ? "1" : "0";
}
}
Now on my View I just display the EditorFor ( ChargeableTrue ), but when I click save it doesn't actually update it.
I think what is happening is that when the model is being updated, it's still attempting to get the value of 'Chargeable' from the View, even though I haven't displayed it there. And since there is no input field, it just gets null and ends up saving that to the database.
if (ModelState.IsValid)
{
db.Entry(call).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
What is one expected to do in this situation?
Based on KMan's answer, here's the extended version just in case you're not familiar with creating view models.
The idea is that your domain object is not really what you want to be updating exactly from your views. Instead, you create a go-between that can also include view-specific items (like a list of objects to populate a drop-down).
public class MyViewModel {
public bool Chargeable { get; set; }
}
Now you can do this:
#* In view *#
Html.EditorFor(m => m.Chargeable)
// In controller
public ActionResult Save(MyViewModel model) {
if (ModelState.IsValid) {
var domainObject = new MyObject() {
Chargeable = model.Chargeable ? "1" : "0"
};
// the rest of your code using domainObject
}
}
I'd consider just creating an overload of your domain object's constructor that accepts your view model to keep the mapping in one place. I typically use a tool like AutoMapper to map objects or manual extension methods.
A view model typically contains a sub-set of your domain object's properties, but can contain all of them or more properties like lists, visbility states, etc. They come in incredibly useful and I've never done a MVC project where I haven't used them.
Use a view model and make your mapping on the controller.
I'm using ASP.NET MVC3, with Entity Framework.
I have a Widget controller, with standard Widget CRUD actions.
In my Create action, I successfully create a new Widget object, which has two FooBar objects. This is added to my database just fine, and the action the redirects to the View action.
[HttpPost]
public ActionResult Create(Widget model)
{
if (ModelState.IsValid)
{
//At this point, the widget has two FooBar properties. I can see the values for these FooBars just fine.
if (repo.AddWidget(model))
{
ViewBag.Message = "Your widget has been created.");
return RedirectToAction("View", new { id = model.Id });
}
else
{
ViewBag.Error = "Woops, something went wrong. Please try again.");
}
}
return View(model);
}
In the View action, I fetch the newly created Widget from my repository - except now the two FooBar properties are null.
public ActionResult View(int id)
{
var widget = repo.GetWidget(id);
if (widget == null)
{
ViewBag.Error = "No widget found for the specified ID";
return RedirectToAction("Find");
}
//At this point, the widget has two null values for the FooBar1 and FooBar 2 properties
return View(widget);
}
In the database itself I can see the correct FooBar ID values on my Widget.
My model is set up pretty much exactly the same as shown in this tutorial:
http://weblogs.asp.net/scottgu/archive/2010/07/16/code-first-development-with-entity-framework-4.aspx
public class WidgetContext : DbContext
{
public DbSet<Widget> Widgets { get; set; }
public DbSet<FooBar> FooBars { get; set; }
}
Can anyone suggest how I might start tracking this issue down?
Update:
I should clarify the values are null whenever I call the View action, not only after a Create.
Looks like FooBar is separate entity and FooBar1 and FooBar2 are navigation properties. In such case you must either explicitly say you want to loade them (we call this eager loading):
var widget = context.Widgets
.Include(w => w.FooBar1)
.Include(w => w.FooBar2)
.SingleOfDefault(w => w.Id == id);
Note: Strongly typed Include requires EF 4.1 for EFv1 or EFv4 use:
var widget = context.Widgets
.Include("FooBar1")
.Include("FooBar2")
.SingleOfDefault(w => w.Id == id);
or create custom strongly typed extension method like this.
or you must turn lazy loading on. Lazy loading makes separate queries to database once properties are first accessed in your view. It requires making both FooBar1 and FooBar2 virtual and context must be alive when view is rendered. Usually this is handled by singe context per HTTP request where context is for example created and disposed in custom controller factory or in custom Http module.
Also next time make your question complete please. You have shown a lot of code but the important parts (Windget class and GetById method) are missing. Unfortuanatelly users here aren't oracles so we need to now necessary details. Both action methods are almost irrelevant to your problem.
I am working on MVC 3. I am trying to create Simliar application as MVC Music Store but I am getting an error. My code is below:
using EFCodeFirst
BookDBContext _db = new BookDBContext();
[ChildActionOnly]
public ActionResult GenreMenu()
{
var categories = _db.Category.ToList();//**Giving error at this pointInvalid object name dbo.Categories**
return PartialView(categories);
}
Verify that your BookDBContext contains a property called Category and that your database contains table dbo.Categories.