@Entity
@Table(name="usertable")
public class Usertable implements Serializable {
	private static final long serialVersionUID = 1L;

	@Id
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	private String userid;

	private String password;

	//bi-directional many-to-one association to Grouptable
	@ManyToOne(cascade={CascadeType.ALL})
    @JoinColumn(name="userid", referencedColumnName="userid")
	private Grouptable grouptable;

    public Usertable() {
    }

	public String getUserid() {
		return this.userid;
	}

	public void setUserid(String userid) {
		this.userid = userid;
	}

	public String getPassword() {
		return this.password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

	public Grouptable getGrouptable() {
		return this.grouptable;
	}

	public void setGrouptable(Grouptable grouptable) {
		this.grouptable = grouptable;
	}
	
}

@Embeddable
public class GrouptablePK implements Serializable {
	//default serial version id, required for serializable classes.
	private static final long serialVersionUID = 1L;

	private String userid;

	private String groupid;

    public GrouptablePK() {
    }
	public String getUserid() {
		return this.userid;
	}
	public void setUserid(String userid) {
		this.userid = userid;
	}
	public String getGroupid() {
		return this.groupid;
	}
	public void setGroupid(String groupid) {
		this.groupid = groupid;
	}

	public boolean equals(Object other) {
		if (this == other) {
			return true;
		}
		if (!(other instanceof GrouptablePK)) {
			return false;
		}
		GrouptablePK castOther = (GrouptablePK)other;
		return 
			this.userid.equals(castOther.userid)
			&& this.groupid.equals(castOther.groupid);

    }
    
	public int hashCode() {
		final int prime = 31;
		int hash = 17;
		hash = hash * prime + this.userid.hashCode();
		hash = hash * prime + this.groupid.hashCode();
		
		return hash;
    }
}

@Entity
@Table(name="grouptable")
public class Grouptable implements Serializable {
	private static final long serialVersionUID = 1L;

	@EmbeddedId
	private GrouptablePK id;

	//bi-directional many-to-one association to Usertable
	@OneToMany(mappedBy="grouptable", cascade={CascadeType.ALL})
	private List<Usertable> usertables;

    public Grouptable() {
    }

	public GrouptablePK getId() {
		return this.id;
	}

	public void setId(GrouptablePK id) {
		this.id = id;
	}
	
	public List<Usertable> getUsertables() {
		return this.usertables;
	}

	public void setUsertables(List<Usertable> usertables) {
		this.usertables = usertables;
	}
	
}