Editing some properties of View Model in ASP.NET MVC - asp.net-mvc

I'm using Entity Framework Database First approach. Let's say I have a model class called Product and that class has a NumberOfViews property. In the Edit page I pass an instance of the product class to the controller.
The problem is I can't add #Html.EditorFor(model => model.NumberOfViews) in the Edit page, because it's supposed that NumberOfViews is updated with every visit to the product page, and NOT by the website Admin.
And I can't add it as #Html.HiddenFor(model => model.NumberOfViews), because if the Admin Inspected the element, he can edit it manually.
Also If I try to programmatically set the value on the server-side (e.g., Product.NumberOfViews = db.Products.Find(Product.Id).NumberOfViews;), I get the following error:
An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.
And if I don't add it to either the view or the controller, the value will be null, thus overriding any previous value.
So what should I do?

I have noticed a lot of people use the same model for their Entity Framework as they do for their MVC Controller. I generally discourage this practice. In my opinion, a database model is not the same as a view model.
Sometimes a view needs less information than what the database model is supplying. For example while modifying account password, view does not need first name, last name, or email address even though they may all reside in the same table.
Sometimes it needs information from more than one database table. For example if a user can store unlimited number of telephone numbers for their profile, then user information will be in user table and then contact information with be in contact table. However when modifying user profile, they may want to add/edit/delete one or more of their numbers, so the view needs all of the numbers along with first name, last name and email address.
This is what I would do in your case:
// This is your Entity Framework Model class
[Table("Product")]
public class Product
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ProductId { get; set; }
public string Name { get; set; }
public int NumberOfPageViews { get; set; }
}
// This is the model you will use in your Edit action.
public class EditProductViewModel
{
public int ProductId { get; set; }
public string Name { get; set; }
}
public class ProductController : Controller
{
IProductService service;
//...
[HttpGet]
public ActionResult Edit(int productId)
{
var product = service.GetProduct(productId);
var model = new EditProductViewModel()
{
ProductId = product.ProductId,
Name = product.Name
};
return View(model);
}
[HttpPost]
public ActionResult Edit(EditProductViewModel model)
{
if (ModelState.IsValid)
{
var product = service.GetProduct(model.ProductId);
product.Name = model.Name;
service.Update(product);
}
// ...
}
}

Related

Adding model to another's models list in MVC 5

So I'm having difficulties with my 'flight order management system' in MVC 5.
What I'm trying to do is to add an existing passenger to a flight using the requirements given in a specific questions.
Must use lists
this is my code:
Flight:
public class Flight
{
public int Id { get; set; }
public string Depart { get; set; }
public string Destination { get; set; }
public DateTime TakeOffTime { get; set; }
public DateTime LandingTime { get; set; }
public virtual List<Passenger> Passengers { get; set; }
}
Passenger:
public class Passagenger
{
public int Id { get; set; }
public string Name { get; set; }
public int Gender { get; set; }
[Range(0,130)]
public int Age { get; set; }
}
We need to make a redirect at the index page (showing all flights) and a redirect link with the details page, where an admin can add a passenger to a flight. He does this by using a dropdown of the existing passengers and a 'add' button.
However, after the 'add' button is pushed, a table needs to pop up showing all passenger on the flight that it redirected to.
How would I approach this? I have already the following controller:
public ActionResult Details()
{
ViewBag.PassengerId = new SelectList(db.Passengers, "Id", "Name");
return View();
}
[HttpPost]
public ActionResult Details(int passengerId)
{
Passenger = db.Passegers.Find(passengerId);
if(ModelState.IsValid)
{
//add the passenger to the selected flight that it redirected to, but how to get the id of it now?
}
//Get all passengers of the flight, how to get the id?
List<Passagier> Passagiers = db.Passagiers.ToList();
return View(Passagiers);
}
My details view:
#using (Html.BeginForm("Details", "Home", FormMethod.Post))
{
#Html.DropDownList("passengerId", (SelectList)ViewBag.PassengersId);
<input type="submit" value="Add" />
}
I can't use anything that the related answers are giving me (viewModel, ienumerable,...) hence why I'm asking this.
How would I be able to pass the current route id of the page (flightID) and the passengersID to the controllers action? What would be a good approach to this?
I am nearly there I think because the redirects work and so does my dropdown list showing all the passengers.
First, any requirements that prohibit good design should be fought against. Project owners pay developers because they do not have the requisite skills, themselves. It is your job as a developer to educate the project owner when there are requirements that do not make sense. If the project owner insists on doing something fundamentally wrong, in spite of your protests, then that's a sign to you to drop them like a hot rock. They will only be a source of problems for you. Don't be afraid to fire clients. There's plenty of fish in the sea, but a bad client will be an anchor around your neck.
That said, you may just be misunderstanding the requirements. While there's places where you can use List<T> and probably even should use List<T>, your database-persisted entity is not one of them. It must be ICollection<T>. Period. A property of List<T> will not be persisted by Entity Framework.
That's where view models come in, as your view model can and should use List<T>, and then you can map that back and forth to the ICollection<T> on your entity. Again, if the requirements prohibit the use of view models, then your client either is uninformed or stupid. Your duty is to make sure they are informed, and if it turns out they're just stupid, then drop them.
Next, whenever you have a list of something you're posting to, you need to use ListBoxFor, rather than DropDownListFor. The latter only allows a single selection, but here you'll need to persist multiple passengers. On your view model, you should have a property like:
public List<int> SelectedPassengerIds { get; set; }
And, then one to hold your passenger options:
public IEnumerable<SelectListItem> PassengerOptions { get; set; }
In your action, you will map the Flight entity to your view model as normal, but for your Passengers collection you would do:
model.SelectedPassengerIds = flight.Passengers.Select(m => m.Id).ToList();
Then, set PassengerOptions:
model.PassengerOptions = db.Passengers.Select(m => new SelectListItem { Value = m.Id.ToString(), Text = m.Name });
Finally, in your view, you'll have:
#Html.ListBoxFor(m => m.SelectedPassengerIds, Model.PassengerOptions)
On post, you need to map on the appropriate posted values from your view model back on to your Flight entity. For your Passengers collection, you will do:
// Remove deselected passengers
flight.Passengers.Where(m => !model.SelectedPassengerIds.Contains(m.Id)).ToList()
.ForEach(m => flight.Passengers.Remove(m));
// Add newly selected passengers
var newPassengerIds = model.SelectedPassengerIds.Except(flight.Passengers.Select(m => m.Id));
db.Passengers.Where(m => newPassengerIds.Contains(m.Id)).ToList()
.ForEach(m => flight.Passengers.Add(m));

Updating many-to-many relationship entity framework

I have problem with updating entites that have many-to many relationship. Below my User and category class:
public class User : IEntity
{
[Key]
public virtual long Id { get; set; }
private ICollection<Category> _availableCategories;
public virtual ICollection<Category> AvailableCategories
{
get { return _availableCategories ?? (_availableCategories = new List<Category>()); }
set { _availableCategories = value; }
}
}
public class Category : IEntity
{
[Key]
public long Id { get; set; }
/// <summary>
/// Full name or description of a category
/// </summary>
[StringLength(255)]
public string FullName { get; set; }
}
This is code snippet from my repository
public override void Edit(User user)
{
var dbUser = _context.Users.Include(x => x.AvailableCategories)
.Single(x => x.Id == user.Id);
var categories = _context.Categories;
dbUser.AvailableCategories.Clear();
foreach (var cat in user.AvailableCategories)
{
dbUser.AvailableCategories.Add(cat);
}
_context.Entry(dbUser).State = EntityState.Modified;
}
However the categories don't get updated. What EF does is insert empty rows into category table and sets relations to this new rows with user.
How can I update User so that I change only categories that already exist in the database?
User that I pass to Edit method has AvailableCategories with only Ids set (rest of properties are empty).
When you're doing something like posting back M2M relationships, you either must post the full object, as in every single property on those objects, or simply post a list of ids and then use those to query the associated objects back from the database. Otherwise, Entity Framework understands your purpose to be to update the properties on the objects as well, in this case with empty values.
Obviously the first option is quite unwieldy, so the second way is the preferred and standard way. Generally, for this, you'd want to use a view model so you could have a property like the following, that you would post into:
public List<long> SelectedCategories { get; set; }
But, if you insist on using the entity directly, you can get much the same result by simply doing:
var selectedCategories = user.AvailableCategories.Select(m => m.Id)
Once you have the ids:
var newAvailableCategories = _context.Categories.Where(m => selectedCategories.Contains(m.Id));
And then finally set that on your user:
dbUser.AvailableCategories = newAvailableCategories;
I notice you are also adding the user.AvailableCategories directly into dbUser.AvailableCategories. I've noticed when binding back complex objects from an MVC view that DB Entities are no longer attached to the DbContext. If you look at the entity, you can verify by checking dbContext.Entry(cat).State is "detached" (or something unexpected) I believe.
You must query those entities back out of the dbContext (possibly by using the returned cat.Id's). Or otherwise manually set the entities as "unchanged". And then add those "non-detached" items into dbUser.AvailableCategories. Please see Chris's answer as it shows with specific code how to get this done.
Also, I might use a linking entity. Possibly something like this:
public class UserCategory
{
public User User {get;set;}
public Category Category {get;set;}
}
And add it to DB context. Also, drop the linking lists in your current User and Category class. This way you can manipulate the UserCategory class (and DbSet) to manage your many-to-many relationship.

Simple approach to CRUD intersection table in MVC ASP.NET and EF?

I am using C#, MVC3, EF5, SQL Server 2008 R2.
I have an intersection table ie
Lecturer -< LecturerCourse >- Course
The list of Lecturers are populated.
When I add a course, it would be neat to have a list of Lecturers that I could select from, that teach the course in question. When I save the new Course record, this multiselect also should save its data back to the "LecturerCourse" table via Model Binding.
I am using EF5.
Can you recommended a simple and standard approach to solving CRUD for a join, ie "LecturerCourse", table? I have looked online, but some of the approaches seem very complicated.
Many thanks.
Alright, it's going to be a long one. To allow this to happen in "one page" (through POST, or you could use Ajax, technically), you need a combination of a Get and Post version of the method and to construct your view model correctly. Below are the classes that I will use for demonstration purposes:
public class NewCourse
{
[Required]
public string Name { get; set; }
// And your other properties
public int[] LecturerIds { get; set; }
}
public class ViewLecturer
{
public int Id { get; set; }
public int Name { get; set; }
}
public class NewCourseViewModel
{
public NewCourse Course { get; set; }
public IEnumerable<ViewLecturer> Lecturers { get; set; }
}
NewCourseViewModel will be the model for the View (see below). ViewLecturer will give you a lighter mapping between your available Lecturer and the information required to Add to them.
As for the Controller:
public class CourseController : Controller, IDisposable
{
private Lazy<YourContext> lazyContext =
new Lazy<YourContext>(() => new YourContext());
private YourContext Context
{
get { return lazyContext.Value; }
}
public ActionResult New()
{
var model = new NewCourseViewModel {
Course = new NewCourse(),
Lecturers = Context.Lecturers
.Select(l => new ViewLecturer { Id = l.Id, Name = l.Name })
};
return View(model);
}
[HttpPost]
public ActionResult New(NewCourse course)
{
if(ModelState.IsValid)
{
var lecturers = course.Lecturers
.Select(l => new Lecturer { Id = l.Id })
.ToList();
foreach(var lecturer in lecturers)
Context.Lecturers.Attach(lecturer);
var newCourse = new Course {
Name = course.Name,
// ... and the rest of the mapping
Lecturer = lecturers
};
context.Courses.Add(newCourse);
context.SaveChanges();
// Could have to handle DbUpdateException if you want
return RedirectToAction(...);
}
return View(new NewCourseViewModel {
Course = course,
Lecturers = Context.Lecturers
.Select(l => new ViewLecturer { Id = l.Id, Name = l.Name })
});
}
public void Dispose()
{
if(lazyContext.IsValueCreated)
lazyContext.Value.Dispose();
}
}
Your first New method will give you the entry point for your Course creation page. The rest of the validation and actual adding will be done through the [HttpPost]overload. As for your View (that should be in the ~/Views/Course/New.cshtml):
#model NewCourseViewModel
// ... Then when you are ready to begin the form
#using(Html.BeginForm("New", "Course", FormMethod.Post))
{
// Your List of Lecturers
#Html.ListBoxFor(m => m.Course.LecturerIds,
new MultiSelectList(
Model.Lecturers,
"Id",
"Name",
m.Course.LecturerIds ?? new int[0]
))
// Your Other Model binding
}
When the submit button will be pressed, the action matched will be the New(NewCourse course). The names are important because of the way the HtmlHelpers generate their Ids. Because we are only included one property of the whole view model, it will match the parameter name course based on the view model's Course property. You will get a list of Ids for the Lecturers which you will be able to use to attach to the DbContext and add directly to the new Course model (Entity Framework will do the rest). In cases where there was a problem, we can get back the list of lecturers and re-use the same NewCourse in the view model.
Now this is example is very basic but it should give you a good starting point as to how you can structure your view model.

Error with relationship

I have a User table and an Avatar table. One User can have many avatars (or null). But I need to mark which avatar is the current, so I have an Avatar_Id in User table that is the current avatar. And a ForeignKey User_Id in Avatar to tell me which User is the owner.
Trying to do that is generating me a lot of errors and headaches when I try to populate some data in order to test the relationship.
public class User
{
[Key]
public int Id { get; set; }
public Avatar Avatar { get; set; }
public virtual ICollection<Avatar> Avatars { get; set; }
}
public class Avatar
{
[Key, ForeignKey("User")]
public int Id { get; set; }
public User User { get; set; }
}
Test part:
var user = new User();
var avatar = new Avatar()
{
User = user
};
// user.Avatar = avatar; // <- this gives [a circular] error; without this I have null.
db.Users.Add(user);
db.Avatars.Add(avatar);
db.SaveChanges();
This is resulting me with Avatar_Id = NULL within User table, and User_Id = NULL in Avatar table. I expected these fields filled (well, Avatar_Id can be null).
Its better to make boolean field 'IsDefault' in table with avatar and check while add/update avatars that no more default avatars for this user. Also you can add same property in avatar class.
#Fabricio I can't test this code before post, but I'm pretty convinced it will work.
public class User
{
[Key]
public int UserId { get; set; }
public int AvatarId { get; set; }
[ForeignKey("AvatarId")]
public Avatar Avatar { get; set; }
public ICollection<Avatar> Avatars { get; set; }
}
public class Avatar
{
[Key]
public int AvatarId { get; set; }
[ForeignKey("User")]
public int UserId { get; set; }
public User User { get; set; }
}
The problem is when you put two foreign keys merge like one. Now you have a foreign key in Avatar table and other in User table, each one represents one mode of relationship.
The foreign key "AvatarId" represents a special form of foreign key, a unique + foreign key, (a second form to build the one to one relationship). You can read more about this in here: http://weblogs.asp.net/manavi/archive/2011/05/01/associations-in-ef-4-1-code-first-part-5-one-to-one-foreign-key-associations.aspx
I've given this a bit of though because I modeled a similar case once and didn't mind to reevaluate the options.
Look closely at your premises:
One User can have many avatars (or null)
This short sentence implies that the one-to-one association User-Avatar must be optional both ways, because a User without Avatars can’t possibly refer to one its own avatars, and when a user has more than one avatar only one of them can refer to User as being the user's default. (They all refer to user as owner).
So you can only model it as a 0..1 – 0..1 association. So Avatar’s primary key can't be a foreign key to user. (It couldn't anyway, otherwise a user could only have one avatar).
Maybe this could have been done by Jonny Piazzi's model if this wouldn't throw the infamous "may cause cycles or multiple cascade paths" exception. Both user and Avatar refer to one another and you have to tell EF explicitly which of the FKs is not cascading. This can only be done by fluent mapping:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<User>()
.HasOptional(u => u.Avatar)
.WithOptionalDependent()
.Map(m => m.MapKey("AvatarId"))
.WillCascadeOnDelete(false);
...
}
This puts a nullable, non-cascading FK column AvatarId in User (that's why User is the dependent of Avatar).
Now your second issue, the chicken-eg problem when populating the model.
This can only be done when you call SaveChanges twice and wrap these calls in a transaction scope. For example:
using (var tran = new TransactionScope())
{
var user = new User();
var avatar = new Avatar();
user.Avatars = new HashSet<Avatar>();
user.Avatars.Add(avatar);
user.Avatars.Add(new Avatar());
user.Avatars.Add(new Avatar());
db.Users.Add(user);
db.SaveChanges();
user.Avatar = avatar; // set FK
db.SaveChanges();
tran.Complete();
}
Now EF can decide which key to generate first (User's) before referring to it by foreign keys. Subsequently you set the FK in User.
But... is this the best model?
Maybe, maybe not.
The issue is that your model does not enforce the business rule that a user can only have one of its own avatars as default avatar. User.AvatarId can refer to any avatar. So you have to write business logic to enforce the business rule.
With YD1m's solution (no User.AvatarId, but a column Avatar.IsDefault) this business rule is enforced implicitly. But now you have to write business logic to enforce that only one avatar is the default.
It's up to you to decide what you think is more feasible.
(for the record: way back, I took the latter option)

MVC, c# .edmx file - Adding a new controller

I am adding a new controller that makes use of a number of tables. I have added these tables to the .edmx file. For the add new controller dialog box, it ask for the Model Class. I do see the 3 tables I dropped into the .edmx but not sure which one to choose or if there is a way to choose a model that is a consolidated version of those 3 tables.
This is where a view model would come into play. First of all create a view model that contains properties for the 3 models you want to render on your view:
public class FakeViewModel
{
public Product Product { get; set; }
public Company Company { get; set; }
public User User { get; set; }
}
In your controller, create a new instance of the view model and populate it accordingly. EG:
public ActionResult FakeAction(int id)
{
var product = _repository.Get<Product>(id);
var company = _repository.Get<Company>();
var user = _repository.Get<user>();
var model = new FakeViewModel{
Product = product,
Company = company,
User = user
};
return View(model);
}
On your view, you will now have a strongly typed view for the FakeViewModel.

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