java - 使用 JSONArray.fromObject 将 Hibernate 实体转换为 json

Question

我在将数据转换为 json 时遇到问题。

Session session = sessionFactory.openSession();       
Affiliate affiliate = (affiliate) session.get( Affiliate , pk );
session.close();
JSONArray.fromObject(affiliate);

调试器显示已获取该行。
但在尝试转换为 json 字符串时出现此异常:

Exception in thread "main" net.sf.json.JSONException: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.affiliates.hibernate.Affiliate.employees, no session or session was closed
at net.sf.json.JSONObject._fromBean(JSONObject.java:959)    ...

这是我的附属实体

    @Entity(name="AFFILIATE")
    @Inheritance(strategy=InheritanceType.SINGLE_TABLE)
    public class Affiliate extends HibernateBean{ 

        @Id
        @GeneratedValue(strategy=GenerationType.IDENTITY) 
        @Column(name="AFFILIATE_ID")
        private long id;

        @ManyToOne(targetEntity = Affiliate.class)
        @JoinColumn(name="PARENT_ID")
        private Affiliate parent;



        @ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.LAZY)
        @JoinTable(name="EMPLOYEES_AFFILIATES"  , joinColumns = {@JoinColumn(name="AFFILIATE_ID")},inverseJoinColumns={@JoinColumn(name="EMPLOYEE_ID")})
        private Set<Employee> employees = new HashSet<Employee>(0);

 getters and setters...

    }

谢谢

Answer 1

您的 employees 集合被标记为 FetchType.LAZY，因此它是延迟获取的，并且在 session 关闭时无法获取。

您有多种选择:

• 如果每次加载 Affiliate 对象时都需要该集合，请将其标记为急切获取:

  @ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER) 
  

• 如果您仅在这种特殊情况下需要该集合，请指示 Hibernate 在这种情况下立即加载它:

  • 使用 JOIN FETCH 子句:

    Affiliate affiliate = (Affiliate) session.createQuery(
        "from Affiliate a join fetch a.employees where a.id = :id")
        .setParameter("id", pk).uniqueResult()
    

  • 使用Hibernate.initialize():

    Affiliate affiliate = (Affiliate) session.get( Affiliate , pk );  
    Hibernate.initialize(affiliate.getEmployees());
    

  • 与 Fetch Profiles

• 在响应准备好之前不要关闭 session 。使用Open Session in View模式。