Spring Data JPA，Hibernate，@ ManyToOne（fetch = FetchType.LAZY）和org.hibernate.LazyInitializationException：无法初始化代理-没有会话

Question

In Employee and Phone example

How to make Hibernate Lazy initialization to work (within Spring Boot)?

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:165) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final]
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:286) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final]
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final]
    at com.example.domain.Employee_$$_jvstb7e_2.toString(Employee_$$_jvstb7e_2.java) ~[bin/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_74]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_74]
    at com.example.domain.Phone.toString(Phone.java:13) ~[bin/:na]
    at com.example.SpringBootQuerydslTestBean$1.run(SpringBootQuerydslTestBean.java:49) ~[bin/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:806) [spring-boot-1.3.5.RELEASE.jar:1.3.5.RELEASE]
    ... 6 common frames omitted

Java code

public class Phone {
    ...
    @ManyToOne(fetch=FetchType.LAZY)
    private Employee owner;

PS Some advises to use FetchType.EAGER like in org.hibernate.LazyInitializationException: could not initialize proxy - no Session , but making Lazy loading work (within Spring Boot, Spring Data JPA) is exactly my goal.

Answer 1

Thanks to M. Deinum for hint.

This particular case was solved by adding toString() in Employee to re-define over Lombok toString()

@Override
    public String toString() {
        return "Employee [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + "]";
    }

also specifying exactly Fetch type

code at https://github.com/paulvi/spring-boot-querydsl

Answer 2

This is happening because of the Lombok instruction @Data, instead of it, use @Getter and @Setter, Follow javadocs from @Data:

Equivalent to @Getter @Setter @RequiredArgsConstructor @ToString @EqualsAndHashCode.

The instruction @ToString generate a implementation of toString method for entire class, so in your JPA return needs to have data for all the object.

Answer 3

我认为您正在尝试在当前会话分离时从代理获取子项，可以在同一会话中获取懒惰的子项。