我想设计一个多对多关系，供学生选择课程。首先，我直接使用多对多关系，然后报告一个错误。因为我是新手，所以我对具体规则不太清楚。我怀疑两个实体之间不能存在两个关系，因此我更改为以下书写方式，但它仍然报告相同的错误。我想我确实遵循了该教程，但是我真的不知道哪里出了问题。因此，我必须寻求帮助。下面是代码。
用户
@Entity
@Table(name = "user")
@JsonIgnoreProperties({"handler", "hibernateLazyInitializer"})
public class User {
private int id;
private int rid;
private String name;
private String password;
private String salt;
private String email;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@Basic
@Column(name = "email")
public String getEmail(){
return email;
}
public void setEmail(String email) {
this.email = email;
}
@Basic
@Column(name = "name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Basic
@Column(name = "password")
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
@Basic
@Column(name = "salt")
public String getSalt() {
return salt;
}
public void setSalt(String salt) {
this.salt = salt;
}
@Basic
@Column(name = "rid")
public int getRid() {
return rid;
}
public void setRid(int rid) {
this.rid = rid;
}
@OneToMany(targetEntity=UserCourse.class,mappedBy = "student")
private List<UserCourse> ars;
public List<UserCourse> getArs() {
return ars;
}
public void setArs(List<UserCourse> ars) {
this.ars = ars;
}
}
课程
@Entity
@Table(name = "course")
@JsonIgnoreProperties({ "handler","hibernateLazyInitializer" })
public class Course {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int id;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@Column(name = "name")
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@ManyToOne
@JoinColumn(name="sid")
private Subject subject;
public Subject getSubject() {
return subject;
}
public void setSubject(Subject subject) {
this.subject = subject;
}
@ManyToOne
@JoinColumn(name="tid")
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
@OneToMany(targetEntity=UserCourse.class,mappedBy = "course")
private List<UserCourse> ars;
public List<UserCourse> getArs() {
return ars;
}
public void setArs(List<UserCourse> ars) {
this.ars = ars;
}
}
UserCourse
@Entity
@Table(name = "user_course")
@JsonIgnoreProperties({ "handler","hibernateLazyInitializer" })
public class UserCourse {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int id;
public void setId(int id) {
this.id = id;
}
public int getId() {
return id;
}
@ManyToOne
@JoinColumn(name = "uid")
private User student;
public User getStudent() {
return student;
}
public void setStudent(User student) {
this.student = student;
}
@ManyToOne
@JoinColumn(name = "cid")
private Course course;
public Course getCourse() {
return course;
}
public void setCourse(Course course) {
this.course = course;
}
}
和错误
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 javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.MappingException: Could not determine type for: java.util.List, at table: user, for columns: [org.hibernate.mapping.Column(ars)]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1796) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:595) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1108) ~[spring-context-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:868) ~[spring-context-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
at com.tz.mooc.Application.main(Application.java:10) [classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_144]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_144]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_144]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_144]
at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.2.2.RELEASE.jar:2.2.2.RELEASE]
Caused by: javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.MappingException: Could not determine type for: java.util.List, at table: user, for columns: [org.hibernate.mapping.Column(ars)]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:403) ~[spring-orm-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:378) ~[spring-orm-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1855) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1792) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
... 21 common frames omitted
Caused by: org.hibernate.MappingException: Could not determine type for: java.util.List, at table: user, for columns: [org.hibernate.mapping.Column(ars)]
at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:488) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:455) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.hibernate.mapping.Property.isValid(Property.java:227) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:624) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.hibernate.mapping.RootClass.validate(RootClass.java:267) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.hibernate.boot.internal.MetadataImpl.validate(MetadataImpl.java:343) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:461) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1237) ~[hibernate-core-5.4.9.Final.jar:5.4.9.Final]
at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) ~[spring-orm-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.2.2.RELEASE.jar:5.2.2.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:391) ~[spring-orm-5.2.2.RELEASE.jar:5.2.2.RELEASE]
... 25 common frames omitted
非常感谢您的帮助
最后，我只是自己在db中创建一个表，然后像对待普通用户表一样对待用户进程表。我认为这不是最好的方法，而且看起来很困惑。也许有人会给我更好的答案。