C#•2y ago

ASP NET MVC, can't show Collection in View, VS say it is null

Hello, I'm working on a MVC Project for a film website (IMDb like). I have a User class and a Person class with a many to many relationship and want to show a User table in this Person detail view.

*@ This is the code inside the cshtml, that I tried using to show the data in the view
<table class="table table-bordered table table-striped" style="width:100%">
        <thead>
            <tr>
                <th>
                    Users
                </th>
            </tr>
        </thead>
        <tbody>
            @if (Model != null && Model.Users != null)
            {
                @foreach (var obj in Model.Users)
                {
                    <tr>
                        <td>
                            @obj.Name
                        </td>

                    </tr>
                }
            }
        </tbody>
    </table>

*@ This is the code inside the cshtml, that I tried using to show the data in the view
<table class="table table-bordered table table-striped" style="width:100%">
        <thead>
            <tr>
                <th>
                    Users
                </th>
            </tr>
        </thead>
        <tbody>
            @if (Model != null && Model.Users != null)
            {
                @foreach (var obj in Model.Users)
                {
                    <tr>
                        <td>
                            @obj.Name
                        </td>

                    </tr>
                }
            }
        </tbody>
    </table>

33 Replies

framoz•2y ago

User and Person class is like shown bellow:

 public class User
    {
      //  [Key]
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public string Email { get; set; }
        [Required]
        public string Password { get; set; }

        public ICollection<Review> Reviews { get; set; }
       // public ICollection<Film> Watched { get; set; }
        public ICollection<Film> Films  { get; set; }
        public ICollection<Person> People { get; set; }
    }

 public class Person
    {
        //  [Key]
        public int Id { get; set; }       
        public string Name { get; set; }
        public string Description { get; set; }        
        public DateTime Birthdate { get; set; }

        [ValidateNever]
        public ICollection<Film> Films { get; set; }
        [ValidateNever]
        public ICollection<User> Users { get; set; }
    }

 public class User
    {
      //  [Key]
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public string Email { get; set; }
        [Required]
        public string Password { get; set; }

        public ICollection<Review> Reviews { get; set; }
       // public ICollection<Film> Watched { get; set; }
        public ICollection<Film> Films  { get; set; }
        public ICollection<Person> People { get; set; }
    }

 public class Person
    {
        //  [Key]
        public int Id { get; set; }       
        public string Name { get; set; }
        public string Description { get; set; }        
        public DateTime Birthdate { get; set; }

        [ValidateNever]
        public ICollection<Film> Films { get; set; }
        [ValidateNever]
        public ICollection<User> Users { get; set; }
    }

Inside my DBContext I have this:

  protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder
                .Entity<User>()
                .HasMany(u => u.People)
                .WithMany(p => p.Users)
                .UsingEntity(j => j.ToTable("UserPeople"));
        }

  protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder
                .Entity<User>()
                .HasMany(u => u.People)
                .WithMany(p => p.Users)
                .UsingEntity(j => j.ToTable("UserPeople"));
        }

I really don't know where else to search or what to do to correct this I'm pretty sure my DB is ok and I made the relation correctly, but I simply can't make this work. I created some users and persons in my db and created the relation between those in an intermediary table "UserPeople" that was created by the modelBuilder

ladyhail•2y ago

Looks like the Model is not passed to the View. Please share Controller code.

framoz•2y ago

@LadyHail thank you for answering, here is the controller code for the view.

  public async Task<IActionResult> Details(int? id)
        {
            if (id == null || _context.People == null)
            {
                return NotFound();
            }

            var person = await _context.People
                .FirstOrDefaultAsync(m => m.Id == id);
            if (person == null)
            {
                return NotFound();
            }

            return View(person);
        }

  public async Task<IActionResult> Details(int? id)
        {
            if (id == null || _context.People == null)
            {
                return NotFound();
            }

            var person = await _context.People
                .FirstOrDefaultAsync(m => m.Id == id);
            if (person == null)
            {
                return NotFound();
            }

            return View(person);
        }

ladyhail•2y ago

In View you need to specify Model type like this: @model Namespace.Person

framoz•2y ago

I think it was already specified :/

ladyhail•2y ago

I suggest debugging what's inside person before returning

framoz•2y ago

apparently the User collection inside Person is null when I debug it, but according to the DB, it should not be. Person1 should have 3 users there

framoz•2y ago

i know these questions may sound a bit dumb, is just that this is my first "serious" project, and I'm kind of lost in some parts of it. Mainly because I don't know what to search to learn what is wrong

ladyhail•2y ago

Is it Entity Framework Core?

framoz•2y ago

yes

ladyhail•2y ago

I think you can find it useful. The relationship needs to be specified via intermediate table. https://www.entityframeworktutorial.net/efcore/configure-many-to-many-relationship-in-ef-core.aspx

Configure Many-to-Many Relationships in Entity Framework Core

Learn how to configure a many-to-many relationship using Fluent API in Entity Framework Core.

framoz•2y ago

I had an intermediate table before, and it was giving me the same error I tried deleting it and making the relation in a different way (this way), but that didn't fixed it :/ I'll make the intermediate table again and try it!

framoz•2y ago

framoz•2y ago

same thing 😭 I created the intermediate one, dropped my DB, made a new one

public class PeopleUsers
    {

        public int UserId { get; set; }
        public int PersonId { get; set; }

        public User User { get; set; }
        public Person Person { get; set; }
    }

public class PeopleUsers
    {

        public int UserId { get; set; }
        public int PersonId { get; set; }

        public User User { get; set; }
        public Person Person { get; set; }
    }

 public class Person
    {
        //  [Key]
        public int Id { get; set; }       
        public string Name { get; set; }
        public string Description { get; set; }        
        public DateTime Birthdate { get; set; }

        [ValidateNever]
        public ICollection<Film> Films { get; set; }
        [ValidateNever]
        public ICollection<PeopleUsers> PeopleUsers { get; set; }
    }


public class User
    {
      //  [Key]
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public string Email { get; set; }
        [Required]
        public string Password { get; set; }

        public ICollection<Review> Reviews { get; set; }
       // public ICollection<Film> Watched { get; set; }
        public ICollection<Film> Films  { get; set; }
        public ICollection<PeopleUsers> PeopleUsers { get; set; }
    }

 public class Person
    {
        //  [Key]
        public int Id { get; set; }       
        public string Name { get; set; }
        public string Description { get; set; }        
        public DateTime Birthdate { get; set; }

        [ValidateNever]
        public ICollection<Film> Films { get; set; }
        [ValidateNever]
        public ICollection<PeopleUsers> PeopleUsers { get; set; }
    }


public class User
    {
      //  [Key]
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public string Email { get; set; }
        [Required]
        public string Password { get; set; }

        public ICollection<Review> Reviews { get; set; }
       // public ICollection<Film> Watched { get; set; }
        public ICollection<Film> Films  { get; set; }
        public ICollection<PeopleUsers> PeopleUsers { get; set; }
    }

DBContexto

 protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            ////Person-Favorite many-to-many relation for favorite person list in User and users that favorited a person in Person
            modelBuilder.Entity<PeopleUsers>()
                .HasKey(pf => new { pf.PersonId, pf.UserId });

            modelBuilder.Entity<PeopleUsers>()
                .HasOne(pf => pf.User)
                .WithMany(u => u.PeopleUsers)
                .HasForeignKey(pf => pf.UserId);

            modelBuilder.Entity<PeopleUsers>()
                .HasOne(pf => pf.Person)
                .WithMany(p => p.PeopleUsers)
                .HasForeignKey(pf => pf.PersonId);

 protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            ////Person-Favorite many-to-many relation for favorite person list in User and users that favorited a person in Person
            modelBuilder.Entity<PeopleUsers>()
                .HasKey(pf => new { pf.PersonId, pf.UserId });

            modelBuilder.Entity<PeopleUsers>()
                .HasOne(pf => pf.User)
                .WithMany(u => u.PeopleUsers)
                .HasForeignKey(pf => pf.UserId);

            modelBuilder.Entity<PeopleUsers>()
                .HasOne(pf => pf.Person)
                .WithMany(p => p.PeopleUsers)
                .HasForeignKey(pf => pf.PersonId);

ladyhail•2y ago

The only difference I see is User -> Id. Following docs it should be UserId and same for person.

framoz•2y ago

in the DBContext?

ladyhail•2y ago

In class definition

framoz•2y ago

In the collections or at the Intermediate class?

ladyhail•2y ago

In the User class property Id rename to UserId

framoz•2y ago

ladyhail•2y ago

Same for Person. Rename Id to PersonId. It shouldn't make a difference, but lets try.

framoz•2y ago

well, it broke my code lol not building, and cant update db

ladyhail•2y ago

You need to drop db and recreate

framoz•2y ago

😭 😭 😭

framoz•2y ago

I'll try again, just a minute I dropped it on MSSMS still cant update it is not building and it dont show me any errors too well, I restored to the last saved version the original one of the post isn't it possible that the error is just on the code in the cshtml?

ladyhail•2y ago

You van try to debug cshtml. But if its null on Controller then it will be null im view

framoz•2y ago

I was thinking if there is another way to write what I want to do inside that foreach

ladyhail•2y ago

The syntax is valid. I'm pretty sure if you follow the tutorial it'll work

framoz•2y ago

made all the changes, following the tutorial, still the same error

framoz•2y ago

it says that PeopleUsers for this Person is null

ladyhail•2y ago

One more idea - in controller before .FirstOrDefault add .Include(x => x.peopleUsers)

framoz•2y ago

i'll try it IT WORKED, THANK YOU SO MUCH someone said something similar in the chat, but I couldnt get it to work you saved my life!

ladyhail•2y ago

You're welcome

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ASP NET MVC, can't show Collection in View, VS say it is null