Why don't virtual fields work for models?

Question

ASP.NET

User Model:

public class User
    {
        [Key]
        public int Id { get; set; }
        public string Email { get; set; }
        public string  FirstName{ get; set; }
        public string LastName { get; set; }
        public string Password { get; set; }
        public int CreatedAt { get; set; }
        public virtual ICollection<Video> Videos { get; set; }
    }

Video model:

public class Video
    {
        [Key]
        public int Id { get; set; }
        public int UserID { get; set; }
        public string Title { get; set; }
        public string Description { get; set; }
        public string File { get; set; }
        public string Hash { get; set; }
        public int CreatedAt { get; set; }
        public int Views { get; set; }
        public virtual User User { get; set; }
    }

When trying to access a virtual field:

@foreach (Video item in Model)
{
        <a href="">@item.User.FirstName</a>
}

Result:

An exception of type 'System.Data.Entity.Core.EntityCommandExecutionException' occurred in EntityFramework.dll but was not handled in user code

Additional information: An error occurred while executing the command definition. See the inner exception for details.

Answer 1

How do you get data from the database? By default, EF does not pull data from related tables.

Answer 2

You are unwinding IQueryable somewhere and inside this process you go to DbContext again for something.
It's hard to be more precise.
See where you work with IQueryable collections.

Answer 3

public class Video
    {
        [Key]
        public int Id { get; set; }
        [ForeignKey("User")]
        public int UserID { get; set; }
        public string Title { get; set; }
        public string Description { get; set; }
        public string File { get; set; }
        public string Hash { get; set; }
        public int CreatedAt { get; set; }
        public int Views { get; set; }
        public virtual User User { get; set; }
    }

Well, the keys must be created at the database level.