用Hibernate建立Membership

@Entity
@Table(name="memberships")
@IdClass(MembershipPK.class)
public class Membership {
	private Integer groupId;

	private Integer userId;

	@Id
	@Column(name="group_id")
	public Integer getGroupId() {
		return groupId;
	}

	public void setGroupId(Integer groupId) {
		this.groupId = groupId;
	}

	@Id
	@Column(name="user_id")
	public Integer getUserId() {
		return userId;
	}

	public void setUserId(Integer userId) {
		this.userId = userId;
	}
}

@Embeddable
public class MembershipPK {
	private Integer groupId;

	private Integer userId;

	public Integer getGroupId() {
		return groupId;
	}

	public void setGroupId(Integer groupId) {
		this.groupId = groupId;
	}
	
	public Integer getUserId() {
		return userId;
	}
	
	public void setUserId(Integer userId) {
		this.userId = userId;
	}
}