org.hibernate.LazyInitializationException：未能延迟初始化角色集合：studentsystem2.ikubinfo.entity.Student.classes

Question

我有这个错误，我找不到发生的原因。 不幸的是，我无法与其他问题联系起来。

SEVERE: Servlet.service() for servlet [rest] in context with path [/studentsystem2] threw exception [Request processing failed; nested exception is org.modelmapper.MappingException: ModelMapper mapping errors:

1) Converter org.modelmapper.internal.converter.CollectionConverter@2f75990d failed to convert java.util.List to java.util.List.

1 error] with root cause
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: studentsystem2.ikubinfo.entity.Student.classes, could not initialize proxy - no Session

这是我的学生 class

学生.java

@Entity
@Table(name="student")
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(name="student_id")
    private long id;

    @NotNull
    @Column(name = "firstname")
    private String firstName;

    @NotNull
    @Column(name = "lastname")
    private String lastName;

    @OneToMany(mappedBy = "student", fetch = FetchType.LAZY)
    private List<Classroom> classes;

    @NotNull
    @Temporal(value = TemporalType.DATE)
    private Date birthdate;

    private boolean flag;

    public Student() {

    }

}

我已经使用 ModelMapper 依赖项从实体转换为 model。 您可以在下面找到 StudentConverter class

StudentConverter.java

@Component
public class StudentConverter {

    private ModelMapper modelMapper = new ModelMapper();

    public StudentConverter() {

    }

    public Student toEntity(StudentModel model) {
        return modelMapper.map(model, Student.class);
    }

    public StudentModel toModel(Student student) {
        return modelMapper.map(student, StudentModel.class);
    }

    public List<StudentModel> toModel(List<Student> entityList) {
        List<StudentModel> modelList = new ArrayList<StudentModel>();
        for (Student student : entityList) {
            modelList.add(toModel(student));
        }
        return modelList;
    }
}

Answer 1

因为 modelmapper 试图在事务上下文之外访问（内部使用反射进行复制）集合（ private List<Classroom> classes; ） Student实体的数据成员。 您必须使用fetch = FetchType.EAGER或者您可以加入以获取此集合以及Student实体。

已编辑

Answer 2

我有同样的问题。 首先，我添加了以下代码：

“fetch = FetchType.EAGER”

但问题并没有解决。

然后，我添加了以下代码，而不是上面的代码：“@LazyCollection (LazyCollectionOption.FALSE)”

问题就解决了。