public class Example
{
    // id и т.д.

    [ForeignKey("CategoryFacetItem")]
    [Display(Name = "Категория")]
    public int? CategoryId { get; set; }
    public virtual FacetItem CategoryFacetItem{ get; set; }
}

public class FacetItem
{
    public int Id { get; set; }
    public int FacetId { get; set; }
    public Facet Facet { get; set; }
    public string Name { get; set; }
}

public async Task<IActionResult> Create([Bind("CategoryId,CategoryFacetItem")] Parcel parcel)