@Entity
    public static class Other {

        @Id
        @GeneratedValue
        private Long id;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
            this.id = id;
        }
    }

    @MappedSuperclass
    public static abstract class Item<T> {
        @ManyToOne( fetch = FetchType.LAZY )
        private T other;

        public T getOther() {
            return other;
        }

        public void setOther(T other) {
            this.other = other;
        }
    }

    @Entity
    public static class ChildItem extends Item<Other> {
        @Id
        @GeneratedValue
        private Long id;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
            this.id = id;
        }
    }