@Entity(name = "MembershipCard")
	public static class MembershipCard {
		@Id
		@Column(name = "card_number")
		private String number;

		@ManyToOne
		@JoinColumn(name = "user_email")
		private Student owner;

		private boolean enabled;
    }
      
    @Entity(name = "Student")
	public static class Student {
		@Id
		private String email;

		private String name;
	}

 create table MembershipCard (
        card_number varchar(255) not null,
        enabled boolean not null,
        user_email varchar(255),
        primary key (card_number)
    )