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public class Category

 [Key]
 [Display(Name = "ID")]
 public int Id get; set; 

 [Display(Name = "Parent Category")]
 public int? ParentId get; set; 

 [Required]
 [Display(Name = "Category Name")]
 public string Name get; set; 

 [Required]
 [Range(0, int.MaxValue)]
 [Display(Name = "Display Order")]
 public int DisplayOrder get; set; 

 [Required]
 [Display(Name = "Active")]
 public bool IsActive get; set; 

 [Display(Name = "Created At")]
 public DateTime CreatedAt get; set; 

 [Display(Name = "Updated At")]
 public DateTime UpdatedAt get; set; 

 [ForeignKey("ParentId")]
 public virtual Category Parent get; set; 

Here is my category modal. I want to this modal to be nested in the select tag like this one:

Vehicle

- Cars

- BMW

-- Audi

Real Estate

- Residential

-- For Sale

etc...

I have used also repository pattern in my project. All required files are mentioned below orderly.

Interfaces:

public interface IRepository<T> where T : class

 IEnumerable<T> List();
 T Find(int? id);
 T Find(Func<T, bool> predicate);
 void Create(T entity);
 void Update(T entity);
 void Delete(T entity);
 int Count(Func<T, bool> predicate);
 void Add(T entity);
 void Save();

public interface ICategoryRepository : IRepository<Category>

 IEnumerable<Category> ListParentCategories();

In the Related View:

@model GoldenStore.Models.ViewModels.CategoryViewModel
@using GoldenStore.Extensions

<select asp-for="Category.ParentId" asp-items="Model.Categories.ToSeceltListItem(Model.Category.Id)" class="input-select">
 <option value="">Main Category</option>
</select>

In the Extensions Folder:

public static class ReflectionExtension

 public static string GetPropertyValue<T>(this T item, string propertyName)
 
 return item.GetType().GetProperty(propertyName).GetValue(item, null).ToString();
 

public static class IEnumerableExtension

 public static IEnumerable<SelectListItem> ToSeceltListItem<T>(this IEnumerable<T> items, int selectedValue)
 
 return from item in items
 select new SelectListItem
 
 Text = item.GetPropertyValue("Name"),
 Value = item.GetPropertyValue("Id"),
 Selected = item.GetPropertyValue("Id").Equals(selectedValue.ToString())
 ;
 

CategoryViewModel:

public class CategoryViewModel

 public Category Category get; set; 
 public IEnumerable<Category> Categories get; set; 

Therefore, what should I do for the nested category like this one:

Vehicle

- Cars

- BMW

-- Audi

Real Estate

- Residential

-- For Sale

etc...