实体类型＆＃39; System.Collections.Generic.IEnumerable`1 [SomeModel]＆＃39;提供参数＆＃39; clrType＆＃39;必须是参考类型

Question

所以，我收到错误消息＆＃34;实体类型＆＃39; System.Collections.Generic.IEnumerable`1 [SomeModel]＆＃39;提供参数＆＃39; clrType＆＃39;必须是参考类型。 ＆＃34;当我尝试添加迁移时。我不知道这里有什么问题。有人可以帮帮忙吗？ 不知道UserRequest类有什么问题。

我看到了一些类似的问题，但继承控制器和类似问题存在问题。

谢谢！欢迎任何帮助！

    public class UserRequest
{
    [ScaffoldColumn(false)]
    [System.ComponentModel.DataAnnotations.Schema.DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public int UserAccountId { get; set; }
    public RequestCode RCode { get; set; }
    public string CodeText { get; set; }
}

public class UserAccount
{
    [ScaffoldColumn(false)]
 [System.ComponentModel.DataAnnotations.Schema.DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]

    public int UserAccountId { get; set; }

    [Required(ErrorMessage = "First Name is required.")]
    public string FirstName { get; set; }
    [Required(ErrorMessage = "Second Name is required.")]
    public string LastName { get; set; }
    [Required(ErrorMessage = "Email is required.")]
    [RegularExpression(@"^([\w-\.]+)@((\[[0-9]{1,3]\.)|(([\w-]+\.)+))([a-zA- 
          Z{2,4}|[0-9]{1,3})(\]?)$",
        ErrorMessage = "Please enter valid email.")]
    public string Email { get; set; }
    [Required(ErrorMessage = "Username is required.")]
    public string UserName { get; set; }
    [Required(ErrorMessage = "Password is required.")]
    [DataType(DataType.Password)]
    public string Password { get; set; }
    [Compare("Password", ErrorMessage = "Please confirm your password.")]
    [DataType(DataType.Password)]
    public string ConfirmPassword { get; set; }

    public Role MyRole { get; set; }

    public UserAccount()
    {
        MyRole = Role.Customer;
    }
}

public class Administrator : UserAccount {
    public IEnumerable<UserRequest> ReceievedRequests { get; set; }
}

public class Customer : UserAccount
{

    public int Spent { get; set; }
    public ShoppingCart Cart { get; set; }
    public virtual IEnumerable<UserRequest> UserRequests { get; set; }
}

DataAccessLayer

public class TalonContext : DbContext
{
    public TalonContext() { }

    public TalonContext(DbContextOptions<TalonContext> options) : 
    base(options) { }

    public DbSet<UserAccount> Users { get; set; }
    public DbSet<UserRequest> Requests { get; set; }


    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Administrator>()
                .HasMany(r => r.ReceievedRequests);

        //modelBuilder.Entity<Customer>()
        //   .HasOne(r => r.UserRequests);

        modelBuilder.Entity<Customer>()           <--fixed
            .HasMany(r => r.UserRequests);

        modelBuilder.Entity<UserRequest>()
            .HasAlternateKey(k => k.UserAccountId);


    }
}