Виктор П.

public class Article
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

       ...

        public virtual ICollection<Comment> comm { get; set; }
    }

public class Comment
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }
        public Guid ArtId { get; set; }
        
       ...

        [ForeignKey("ArtId")]
        public virtual Article art { get; set; }
    }