我有一个Spring Boot项目,其中包含一些实体。具体来说,我有一个“学生”类,其中包含一个“期望课程列表”,应该是一个Set<>。
当我使用以下代码时:
@OneToMany(mappedBy = "student", cascade = CascadeType.ALL)
public List<StudentDesiredCourseEntity> getStudentDesiredCourses() {
return studentDesiredCourses;
}
public void setStudentDesiredCourses(List<StudentDesiredCourseEntity> studentDesiredCourses) {
this.studentDesiredCourses = studentDesiredCourses;
}
一切正常,但当我使用
@OneToMany(mappedBy = "student", cascade = CascadeType.ALL)
public Set<StudentDesiredCourseEntity> getStudentDesiredCourses() {
return studentDesiredCourses;
}
public void setStudentDesiredCourses(Set<StudentDesiredCourseEntity> studentDesiredCourses) {
this.studentDesiredCourses = studentDesiredCourses;
}
我获取
org.springframework.http.converter.HttpMessageNotReadableException",
"message":"Could not read JSON: (was java.lang.NullPointerException) (through reference chain: edu.cs6310.project4.entities.StudentEntity[\"studentDesiredCourses\"]->java.util.HashSet[0]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: edu.cs6310.project4.entities.StudentEntity[\"studentDesiredCourses\"]->java.util.HashSet[0])
我是否漏掉了什么或需要额外做些什么?
根据要求,需要编写equals和hashcode方法。
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof StudentDesiredCourseEntity)) return false;
StudentDesiredCourseEntity that = (StudentDesiredCourseEntity) o;
if (!course.equals(that.course)) return false;
if (!priority.equals(that.priority)) return false;
if (!student.equals(that.student)) return false;
return true;
}
@Override
public int hashCode() {
int result = priority.hashCode();
result = 31 * result + course.hashCode();
result = 31 * result + student.hashCode();
return result;
}