C# .NET core 3 MVC Scaffolding with EntityFrameworkCore

Question

I have to following many-to-many model structure:

 public class User
    {    
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid UserId { get; set; }

        [Required]
        [MaxLength(50)]
        public string Name{ get; set; }

        [Required]
        [MaxLength(50)]
        public string Email { get; set; }

        
        public virtual ICollection<UserInRole> UserInRoles { get; set; }
   }

 public class Role
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int RoleId { get; set; }
        public string RoleName { get; set; }
                
        public virtual ICollection<UserInRole> UserInRoles { get; set; }
    }


 public class UserInRole
    {
        [Required]        
        public Guid UserId { get; set; }
    
        [Required]       
        public int RoleId { get; set; }
    
    
        public virtual User User { get; set; }
        public virtual Role Role { get; set; }
    }

ApplicationDbContext:

 protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            

            // UserInRole: set both fields as primary
            modelBuilder.Entity<UserInRole>().HasKey(table => new{ table.RoleId, table.UserId});


            modelBuilder.Entity<User>()
                .HasMany(c => c.UserInRoles);


            modelBuilder.Entity<Role>()
                .HasMany(c => c.UserInRoles);

The database is successfully created with the right relationships (many to many) but when I create a new Controller & View using scaffolding - the system generates the CRUD pages without the option to select the role for each user. is it normal? do I need to do this part by myself?

Miraziz · Accepted Answer · 2021-01-23 15:01:03Z

Yes, as far as I remember you should render one-to-many relations in your views manually.

One of the easiest way I know:

<div class="form-group">
            <label asp-for="User" class="control-label"></label>
            <select asp-for="UserId"
                    class="form-control"
                    asp-items="@(new SelectList(ViewBag.Users, "UserId", "Name"))">
            </select>
        </div>
        <div class="form-group">
            <label asp-for="Role"></label>
            <select asp-for="RoleId"
                    class="form-control"
                    asp-items="@(new SelectList(ViewBag.Roles, "RoleId", "RoleName"))">
            </select>
        </div>

In this example, you send UsersList and RolesList to the View by ViewBag as a SelectList and then render them on View. So as far as I know you need to do it manually to render one-to-many or many-to-many relations because the list needs to be converted to the SelectList for the view to know how to work with it.

You can also take a look at here

Serge · Accepted Answer · 2021-01-23 18:54:49Z

1

To create a select control, at first you will have to create a list of SelectItem from the Role list:


var roleItems=dbcontext.Roles.Select(i=> new SelectListItem {
Value=i.RoleId.ToString(),
Text=i.RoleName
}).ToArray();

You can use a viewbag to keep the list for the view, but it is a better idea to create a ViewModel class like this

public UserViewModel
{
public User User {get; set;}
public SelectListItem[] RoleItems {get; set;} 
}

After this you can use this list to create a select input. You can use the sample from @Miraziz answer.

answered Jan 23, 2021 at 18:54

Serge

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