How do I populate dropdown list from foreign key value in MVC view?

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C#

ViewModel

MVC5

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I have 3 tables subject , topic and sub topic. topic has subjectID as foreign key while subtopic has topic id as foreign key. I am using EF6 DB First to generate model classes.

I have created the Create view for subject which works fine. Now i want to create a create view for Topic. after scaffolding it created the view for me and i can see the dropdownlist code generated there for subjects. when when i run it i get error
"

There is no ViewData item of type 'IEnumerable<SelectListItem>' that has the key 'SubjectId

"

So i get that since i am not passing anything to the get method , it can't populate the dropdown. My question is how do i do so.'

this is my subject class

public partial class Subject
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public Subject()
        {
            this.Topics = new HashSet<Topic>();
        }
    
        public int Id { get; set; }
        public string SubjectName { get; set; }
        public string LogoPath { get; set; }
        public string LogoName { get; set; }
        public Nullable<System.DateTime> CreatedDate { get; set; }
        public Nullable<System.DateTime> ModifiedDate { get; set; }
        public Nullable<bool> IsActive { get; set; }
    
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<Topic> Topics { get; set; }
    }

this is topic class

public partial class Topic
   {
       [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
       public Topic()
       {
           this.SubTopics = new HashSet<SubTopic>();
       }

       public int Id { get; set; }
       public Nullable<int> SubjectId { get; set; }
       public string TopicName { get; set; }
       public string TopicLogoPath { get; set; }
       public string TopicLogoName { get; set; }
       public string Description { get; set; }
       public Nullable<System.DateTime> CreatedDate { get; set; }
       public Nullable<System.DateTime> ModifiedDate { get; set; }
       public Nullable<bool> IsActive { get; set; }

       public virtual Subject Subject { get; set; }
       [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
       public virtual ICollection<SubTopic> SubTopics { get; set; }
   }

What is the correct way to pupulate subject dropdown in Topic and Topic dropdown in subtopic.
Any sort help is much appreciated.

Thanks

What I have tried:

I tried creating a ViewModel Class with an IEnumerable<subject> feild. I then populated this feild in a get method which i then pass to the view.

public class TopicVM
   {
       public int Id { get; set; }
       public Nullable<int> SubjectId { get; set; }
       public string TopicName { get; set; }
       public string TopicLogoPath { get; set; }
       public string TopicLogoName { get; set; }
       public string Description { get; set; }
       public Nullable<System.DateTime> CreatedDate { get; set; }
       public Nullable<System.DateTime> ModifiedDate { get; set; }
       public Nullable<bool> IsActive { get; set; }

       public IEnumerable<Subject> Subjects { get; set; }

   }

this is the method that populates the property

public TopicVM GetList()
        {
            TopicVM topicVM = new TopicVM();
            topicVM.Subjects = _entities.Subjects.Where(x => x.IsActive == true).Select(x=>x).ToList();
            return topicVM;
        }

Now when i am trying to add view using TopicVM as the model class i recieve error that "Unable to retreive metadata for QR.ViewModels.TopicVM"