Java @我的springboot应用程序中的OneToOne或@ManyToOne错误

这是我的课程。java类，一个主题可以有多个类。当我运行我的程序时，我得到两个异常，一个是BeanCreationException，另一个是AnnotationException。我在下面用spring控制台日志附加了我代码的所有类

package com.shashank.courses;
import topic.Topic;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Course {

@Id
private String id;
private String name;
private String description;

// There can be many courses under the topics
@ManyToOne
private Topic topic;

public Course() {

}

public Course(String id, String name, String description, String topicId) {
    super();
    this.id = id;
    this.name = name;
    this.description = description;
    this.topic = new Topic(topicId, "", "");
}

public String getId() {

    return id;
}

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

public String getName() {

    return name;
}

public void setName(String name) {

    this.name = name;
}

public String getDescription() {

    return description;
}

public void setDescription(String description) {

    this.description = description;
}

public Topic getTopic() {
    return topic;
}

public void setTopic(Topic topic) {
    this.topic = topic;
}
}

这是我的CourseController.java

package com.shashank.courses;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import topic.Topic;
import java.util.List;
import java.util.Optional;

@RestController
public class CourseController {

@Autowired
private CourseService courseService;

@RequestMapping("/topics/{id}/courses")
public List<Course> getAllCourses(@PathVariable String id) {
    return courseService.getAllCourses(id);
}

// {} for variable portion
@RequestMapping("/topics/{topicId}/courses/{id}")
public Optional<Course> getCourse(@PathVariable String id) {
    return courseService.getCourse(id);
}

@RequestMapping(method = RequestMethod.POST, value = "/topics/{topicId}/courses")
public void addCourse(@RequestBody Course course, @PathVariable String topicId) {
    course.setTopic(new Topic(topicId, "",""));
    courseService.addCourse(course);
}

@RequestMapping(method = RequestMethod.PUT, value = "/topics/{topicId}/courses/{id}")
public void updateCourse(@RequestBody Course course, @PathVariable String topicId, @PathVariable String id) {
    course.setTopic(new Topic(topicId, "",""));
    courseService.updateCourse( course);
}

     @RequestMapping(method = RequestMethod.DELETE, value = "/topics/{topicId}/courses/{id}")
     public void deleteCourse(@PathVariable String id) {
    courseService.deleteCourse(id);
}
}

package com.shashank.courses;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

@Service
public class CourseService {

@Autowired
private CourseRepository courseRepository;

public List<Course> getAllCourses(String topicId) {

    List<Course> courses = new ArrayList<>();
    courseRepository.findByTopicId(topicId).forEach(courses::add);
    return courses;
}

public Optional<Course> getCourse(String id) {
    return courseRepository.findById(id);
}

public void addCourse(Course course) {
    courseRepository.save(course);
}

public void updateCourse(Course course) {
    courseRepository.save(course);
}

public void deleteCourse(String id) {
    courseRepository.deleteById(id);
}
}

这是我的Spring控制台日志

Error starting ApplicationContext. To display the conditions report re-run your application with 
'debug' enabled.
2021-03-04 16:23:05.108 ERROR 14500 --- [main] o.s.boot.SpringApplication               : 
Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 
'entityManagerFactory' defined in class path resource 
[org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init 
method failed; nested exception is org.hibernate.AnnotationException: @OneToOne or @ManyToOne on 
com.shashank.courses.Course.topic references an unknown entity: topic.Topic

Caused by: org.hibernate.AnnotationException: @OneToOne or @ManyToOne on 
com.shashank.courses.Course.topic references an unknown entity: topic.Topic
at org.hibernate.cfg.ToOneFkSecondPass.doSecondPass(ToOneFkSecondPass.java:97) ~[hibernate-core- 
5.4.28.Final.jar:5.4.28.Final]

---

你应该有一套关于你的主题课的

课程

：

@OneToMany(mappedBy = "topic")
private List<Course> courseList;

---

对于关系，您需要这样的sintax：

 @OneToMany(mappedBy="cart")
private List<Items> items;

@ManyToOne
@JoinColumn(name="cart_id", nullable=false)
private Cart cart;

@OneToMany（mappedBy=“cart”）
私人清单项目；
@许多酮
@JoinColumn（name=“cart\u id”，nullable=false）
私家车；

com.shashank.courses.courses.topic引用了一个未知实体：topic.topic:这意味着Spring Boot找不到topic实体，因此它无法创建课程实体，因为存在多通关系，所以应用程序无法启动，因为存在BeanCreationException

查看您的代码，我可以看到Topic类在“Topic”包中，但其他所有类/接口都在“com.shashank.courses”包中

假设您使用“com.shashank.courses”包作为应用程序的主包，SpringBoot将扫描此包以创建它所需的bean。但是由于Topic类位于不同的包中，因此它无法创建topicbean

如果是这种情况，则有两种选择：

将主题类移到“com.shashank.courses”包中

在具有@SpringBootApplication的类上使用正确的@EntityScan注释

资料来源：

@OneToMany(mappedBy = "topic")
private List<Course> courseList;

@ManyToOne
@JoinColumn(name = "topic_id", nullable = false)
private Topic topic;

 @OneToMany(mappedBy="cart")
private List<Items> items;

@ManyToOne
@JoinColumn(name="cart_id", nullable=false)
private Cart cart;