EntityType 'MultiString' не имеет определенного ключа. Определите ключ для этого EntityType

Question

Я использую сначала код для своего проекта. и в моей базе данных есть информация. Теперь я хочу добавить поле [Display(Name = "ParentGroup", ResourceType = typeof(Resources))] в Title в моей модели. Но я получаю эту ошибку:

WebSite.Models.MultiString: : EntityType 'MultiString' has no key defined. Define the key for this EntityType.
MultiStrings: EntityType: EntitySet 'MultiStrings' is based on type 'MultiString' that has no keys defined.

это моя модель:

 public class Group
{
    [Display(Name = "Id", ResourceType = typeof(Resources))]
    public int Id { get; set; }


    [Required(ErrorMessageResourceName = "Required", ErrorMessageResourceType = typeof(Resources))]
    [Display(Name = "Priority", ResourceType = typeof(Resources))]
    public int Priority { get; set; }

    [Required(ErrorMessageResourceName = "Required", ErrorMessageResourceType = typeof(Resources))]
    [Display(Name = "Title", ResourceType = typeof(Resources))]
    public MultiString Title { get; set; }

    
    [Display(Name = "ParentGroup", ResourceType = typeof(Resources))]
    public Nullable<int> ParentId { get; set; }

    [ForeignKey("ParentId")]
    [Display(Name = "ParentGroup", ResourceType = typeof(Resources))]
    public virtual Group Parent { get; set; }

    
    [Display(Name = "Abstract", ResourceType = typeof(Resources))]
    public MultiString Abstract { get; set; }

    
    [Display(Name = "Context", ResourceType = typeof(Resources))]
    public MultiHtml Context { get; set; }

   
    [Display(Name = "Active", ResourceType = typeof(Resources))]
    public bool Active { get; set; }

   
    [MaxLength(450, ErrorMessageResourceName = "MaxLength", ErrorMessageResourceType = typeof(Resources))]
    [Display(Name = "ImageUrl", ResourceType = typeof(Resources))]
    public string ImageUrl { get; set; }

    [NotMapped]
    public bool Leaf { get; set; }
    public virtual ICollection<Product> Products { get; set; }

    public virtual ICollection<Price> Prices { get; set; }
    [Display(Name = "لیست مشخصه ها")]

    public virtual ICollection<GroupProperty> Properties { get; set; }
    [NotMapped]
    public List<Group> Child { get;  set; }
}

}

У кого-то есть решение?