为什么在春季启动应用程序的一对多关系中子集合为空？

Question

我使用mysql，JPA，Web依赖项创建一个Spring启动应用程序，并在Spring启动的.properties文件中手动配置我的数据库设置。我通过编译，并成功启动应用程序，添加一条记录是正常的。

但是，我使用方法'findAll（Pageable pageable）'我遇到了问题，就是这样

Could not write JSON: failed to lazily initialize a collection of role，could not initialize proxy - no Session

我感到困惑，我开始调试我的代码，最后我发现结果的子集合为null，它包含一个错误，这是

"Exception occurred: com.sun.jdi.InvocationException occurred invoking method.."

我尝试了很多来修复我的代码，但没有用。谁能帮我？

实体关系是一个简单的一对多：TeacherInfo实体和ClassInfo实体，教师管理多个类，就这么简单。

这是我的应用程序的输入点：

@SpringBootApplication(exclude= {
        DataSourceAutoConfiguration.class,
        HibernateJpaAutoConfiguration.class,
        DataSourceAutoConfiguration.class
})
@EnableTransactionManagement
public class OrmTestApplication {

    public static void main(String[] args) {
        SpringApplication.run(OrmTestApplication.class, args);
    }
}

数据库属性设置如下：

spring.datasource.primary.url=jdbc:mysql://localhost:3306/ormtest?useSSL=false
spring.datasource.primary.username=root
spring.datasource.primary.password=BlaNok2700
spring.datasource.primary.driver-class-name = com.mysql.jdbc.Driver

hibernate.hbm2ddl.auto = update
hibernate.show-sql = true

我的数据库配置java代码在这里：

Configuration
@EnableJpaRepositories(basePackages = "com.lanjian.ormtest.repositories", entityManagerFactoryRef = "primaryEntityManagerFactory", transactionManagerRef = "primaryTransactionManager")
public class PrimaryDbConfig {

@Autowired
private Environment env;

@Bean
@ConfigurationProperties(prefix="spring.datasource.primary")
public DataSourceProperties primaryDataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
public DataSource primaryDataSource() {
    DataSourceProperties dbProperty = primaryDataSourceProperties();
    return DataSourceBuilder.create()
            .driverClassName(dbProperty.getDriverClassName())
            .url(dbProperty.getUrl())
            .username(dbProperty.getUsername())
            .password(dbProperty.getPassword())
            .build();
}

@Bean
public LocalContainerEntityManagerFactoryBean primaryEntityManagerFactory() {
    LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
    factory.setDataSource(primaryDataSource());
    factory.setPackagesToScan("com.lanjian.ormtest.entities");
    factory.setJpaVendorAdapter(new HibernateJpaVendorAdapter());

    Properties jpaProperties = new Properties();
    jpaProperties.put("hibernate.hbm2ddl.auto", env.getProperty("hibernate.hbm2ddl.auto"));
    jpaProperties.put("hibernate.show-sql", env.getProperty("hibernate.show-sql"));
    factory.setJpaProperties(jpaProperties);
    return factory;
}

@Bean
public PlatformTransactionManager primaryTransactionManager() {
    EntityManagerFactory factory = primaryEntityManagerFactory().getObject();
    return new JpaTransactionManager(factory);
}

}

我的REST控制器方法在这里：

@Autowired
private TeacherRepository teacherRepository;

@GetMapping("/page")
public Page<TeacherInfo> page(Pageable pageable){
    Page<TeacherInfo> list = teacherRepository.findAll(pageable);
    return list;
}

发生了什么在我开始我的应用程序，并使用邮递员发送请求后，我得到了这个：got a 500 error

我调试我的代码，发现这个：child collection is null在图片中，'classes'是一个列表集合，但它是null，我不明白。

这是我定义的TeacherInfo实体

@Entity
@Table(name = "teacher")
public class TeacherInfo {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

private String name;

private byte age;

private boolean male;

@OneToMany(cascade = CascadeType.ALL,fetch = FetchType.LAZY, mappedBy="chargedTeacher")
private List<ClassInfo> classes = new ArrayList<>();

public void initialize() {
    for (ClassInfo classInfo : classes) {
        classInfo.setChargedTeacher(this);
        for (StudentInfo studentInfo : classInfo.getStudents()) {
            studentInfo.setClassInfo(classInfo);
        }
    }
}
//Setters and Getters}

这是我定义的ClassInfo实体

@Entity
@Table(name = "class_info")
 public class ClassInfo {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

private String name;

private int capacity;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "teacher_id",nullable=false)
@JsonIgnore
private TeacherInfo chargedTeacher;

@OneToMany(cascade = CascadeType.ALL,fetch=FetchType.LAZY,mappedBy="classInfo")
private List<StudentInfo> students = new ArrayList<>();

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getCapacity() {
    return capacity;
}

public void setCapacity(int capacity) {
    this.capacity = capacity;
}

public TeacherInfo getChargedTeacher() {
    return chargedTeacher;
}

public void setChargedTeacher(TeacherInfo chargedTeacher) {
    this.chargedTeacher = chargedTeacher;
}

public List<StudentInfo> getStudents() {
    return students;
}

public void setStudents(List<StudentInfo> students) {
    this.students = students;
}

}