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这篇文章主要讲解了“ManyToMany单向和双向@JoinTable的使用方法是什么”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“ManyToMany单向和双向@JoinTable的使用方法是什么”吧！
单向是指类层面，在下面例子中老师类可以知道要教哪些学生，学生不知被哪些老师教
**需要用到连接表**@JoinTable(name="t_s",
joinColumns={@JoinColumn(name="teacher_id")},inverseJoinColumns={@JoinColumn(name="student_id")}
)也可以不用连接表，但是若不用连接表，表名、列名规则：
在student表中没有写外键则会用对方的表名_主键名
在teacher表中有外键，则会s_id（也是student的主键名）
表名是student_teacher
student类
@Entity
public class student {
private int id;
private String name;
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}Teacher类
@Entity
public class teacher {
private int id;
private String name;
private Set<student> s=new HashSet<student>();
@Id //必须加在getId上面
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@ManyToMany
@JoinTable(name="t_s",
joinColumns={@JoinColumn(name="teacher_id")},inverseJoinColumns={@JoinColumn(name="student_id")}
)//将会以上两个字段为联合主键
//定义中间表的名称，列名：joinColumns，inverseJoinColumns是预防组合主键的时候。
public Set<student> getS() {
return s;
}
public void setS(Set<student> s) {
this.s = s;
}
}也可以用@JoinTable对连接表字段名进行修改
@Entity
public class student {
private int id;
private String name;
private Set<teacher> ts=new HashSet<teacher>();
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@ManyToMany
@JoinTable(name="t_s",
joinColumns={@JoinColumn(name="teacher_id")},inverseJoinColumns={@JoinColumn(name="student_id")}
)
public Set<teacher> getTs() {
return ts;
}
public void setTs(Set<teacher> ts) {
this.ts = ts;
}
}@Entity
public class teacher {
private int id;
private String name;
private Set<student> s=new HashSet<student>();
@Id //必须加在getId上面
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@ManyToMany(mappedBy="ts")
//定义中间表的名称，列名：joinColumns，inverseJoinColumns是预防组合主键的时候。
public Set<student> getS() {
return s;
}
public void setS(Set<student> s) {
this.s = s;
}
}DeviceGroup类
package com.sunwave.grouping.domain;
import javax.persistence.*;
import java.io.Serializable;
import java.util.List;
@Entity
@Table(name = "device_group")
public class DeviceGroup implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
/* @Column(name="group_id")*/
private long groupId;
@Column(name="group_name")
private String groupName;
@Column(name="description")
private String description;//自动在数据库里生成了group_has_element表，该表包括group_id和element_id两个字段，该表主要是用于存储device_group表和ne_element表的对应关系。
@ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)//表的关联，生成一个group_has_element中间表。
@JoinTable(name = "group_has_element",joinColumns = {@JoinColumn(name = "group_id",referencedColumnName = "groupId")}
,inverseJoinColumns = {@JoinColumn(name = "element_id",referencedColumnName = "neNeid")})
private List<NeElement> elementList;
public List<NeElement> getElementList() {
return elementList;
}
public void setElementList(List<NeElement> elementList) {
this.elementList = elementList;
}
public long getGroupId() {
return groupId;
}
public void setGroupId(long groupId) {
this.groupId = groupId;
}
public String getGroupName() {
return groupName;
}
public void setGroupName(String groupName) {
this.groupName = groupName;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
@Override
public String toString() {
return "DeviceGroup [groupId=" + groupId + ", groupName=" + groupName + ", description=" + description
+ ", elementList=" + elementList + "]";
}
}NeElement 类
package com.sunwave.grouping.domain;
import javax.persistence.*;
import java.io.Serializable;
import java.util.Date;
import java.util.List;
/**
* @author lfw
* @date 2020年8月3日
* @time 下午6:44:54
*
*/
@Entity
@Table(name = "ne_element")
public class NeElement implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long neNeid; //设备唯一标识
private String coonReqUrl; //设备连接URL
private String serialNumber; //设备序列号
private String deviceIp; //设备IP
private Long modelId;//modelName对应的id
private String description;//描述
private String manufacturer;//制造商
private String softwareVersion;//软件版本
private Date creationTime;//创建时间
private Date lastBootstrapTime;
private Date lastConnTime;//最后连接时间
private Date updateTime;//更新时间
private String oui;//oui
private String product;
private Boolean authRequirement;//是否需要认证
private String dialectIP;
private String updateUser;//更新用户
private String macAddress;//mac地址
private Integer onlineStatus;//在线状态
private Integer sessionStatus;//会话状态
@ManyToMany(mappedBy = "elementList")
private List<DeviceGroup> deviceGroupList;
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public String getManufacturer() {
return manufacturer;
}
public void setManufacturer(String manufacturer) {
this.manufacturer = manufacturer;
}
public String getSoftwareVersion() {
return softwareVersion;
}
public void setSoftwareVersion(String softwareVersion) {
this.softwareVersion = softwareVersion;
}
public Date getLastConnTime() {
return lastConnTime;
}
public void setLastConnTime(Date lastConnTime) {
this.lastConnTime = lastConnTime;
}
public Long getModelId() {
return modelId;
}
public void setModelId(Long modelId) {
this.modelId = modelId;
}
public Long getNeNeid() {
return neNeid;
}
public void setNeNeid(Long neNeid) {
this.neNeid = neNeid;
}
public String getCoonReqUrl() {
return coonReqUrl;
}
public void setCoonReqUrl(String coonReqUrl) {
this.coonReqUrl = coonReqUrl;
}
public String getDeviceIp() {
return deviceIp;
}
public void setDeviceIp(String deviceIp) {
this.deviceIp = deviceIp;
}
public String getSerialNumber() {
return serialNumber;
}
public void setSerialNumber(String serialNumber) {
this.serialNumber = serialNumber;
}
public Date getCreationTime() {
return creationTime;
}
public void setCreationTime(Date creationTime) {
this.creationTime = creationTime;
}
public Date getLastBootstrapTime() {
return lastBootstrapTime;
}
public void setLastBootstrapTime(Date lastBootstrapTime) {
this.lastBootstrapTime = lastBootstrapTime;
}
public Date getUpdateTime() {
return updateTime;
}
public void setUpdateTime(Date updateTime) {
this.updateTime = updateTime;
}
public String getOui() {
return oui;
}
public void setOui(String oui) {
this.oui = oui;
}
public String getProduct() {
return product;
}
public void setProduct(String product) {
this.product = product;
}
public Boolean getAuthRequirement() {
return authRequirement;
}
public void setAuthRequirement(Boolean authRequirement) {
this.authRequirement = authRequirement;
}
public String getDialectIP() {
return dialectIP;
}
public void setDialectIP(String dialectIP) {
this.dialectIP = dialectIP;
}
public String getUpdateUser() {
return updateUser;
}
public void setUpdateUser(String updateUser) {
this.updateUser = updateUser;
}
public String getMacAddress() {
return macAddress;
}
public void setMacAddress(String macAddress) {
this.macAddress = macAddress;
}
public Integer getOnlineStatus() {
return onlineStatus;
}
public void setOnlineStatus(Integer onlineStatus) {
this.onlineStatus = onlineStatus;
}
public Integer getSessionStatus() {
return sessionStatus;
}
public void setSessionStatus(Integer sessionStatus) {
this.sessionStatus = sessionStatus;
}
}以上为多对多关系的使用，大家可以参考，本人在使用过程中遇到以下报错信息：
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: Unable to map collection com.sunwave.grouping.domain.DeviceGroup.elementList
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1694) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:573) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1087) ~[spring-context-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:857) ~[spring-context-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:548) ~[spring-context-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.0.8.RELEASE.jar:2.0.8.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) [spring-boot-2.0.8.RELEASE.jar:2.0.8.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:386) [spring-boot-2.0.8.RELEASE.jar:2.0.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:307) [spring-boot-2.0.8.RELEASE.jar:2.0.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1242) [spring-boot-2.0.8.RELEASE.jar:2.0.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1230) [spring-boot-2.0.8.RELEASE.jar:2.0.8.RELEASE]
at com.sunwave.Application.main(Application.java:26) [classes/:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]
at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.0.8.RELEASE.jar:2.0.8.RELEASE]
Caused by: org.hibernate.AnnotationException: Unable to map collection com.sunwave.grouping.domain.DeviceGroup.elementList
at org.hibernate.cfg.annotations.CollectionBinder.bindCollectionSecondPass(CollectionBinder.java:1621) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.cfg.annotations.CollectionBinder.bindManyToManySecondPass(CollectionBinder.java:1352) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.cfg.annotations.CollectionBinder.bindStarToManySecondPass(CollectionBinder.java:810) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.cfg.annotations.CollectionBinder$1.secondPass(CollectionBinder.java:735) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:54) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1640) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1608) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:278) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:861) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:888) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:57) ~[spring-orm-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:390) ~[spring-orm-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:377) ~[spring-orm-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1753) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1690) ~[spring-beans-5.0.12.RELEASE.jar:5.0.12.RELEASE]
... 21 common frames omitted
Caused by: org.hibernate.cfg.RecoverableException: Unable to find column with logical name: groupId in org.hibernate.mapping.Table(device_group) and its related supertables and secondary tables
at org.hibernate.cfg.Ejb3JoinColumn.checkReferencedColumnsType(Ejb3JoinColumn.java:837) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.cfg.BinderHelper.createSyntheticPropertyReference(BinderHelper.java:244) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.cfg.annotations.CollectionBinder.bindCollectionSecondPass(CollectionBinder.java:1611) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
... 37 common frames omitted
Caused by: org.hibernate.MappingException: Unable to find column with logical name: groupId in org.hibernate.mapping.Table(device_group) and its related supertables and secondary tables
at org.hibernate.cfg.Ejb3JoinColumn.checkReferencedColumnsType(Ejb3JoinColumn.java:832) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
... 39 common frames omitted
检查了实体类和数据库发现没有什么错，原来是因为我的实体类里的groupId上用了/*@Column(name=“group_id”)注解，如下把该注解注释掉或者删除掉就可以了。
/* @Column(name="group_id")*/ private long groupId;
感谢各位的阅读，以上就是“ManyToMany单向和双向@JoinTable的使用方法是什么”的内容了，经过本文的学习后，相信大家对ManyToMany单向和双向@JoinTable的使用方法是什么这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！
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