兄弟，干蛤呢？喝杯Java再走吧！
@ManyToMany(多对多关系)使用小结！
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 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;}@Overridepublic 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URLprivate String serialNumber; //设备序列号private String deviceIp; //设备IPprivate Long modelId;//modelName对应的idprivate 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;//ouiprivate 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.elementListat 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.elementListat 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 tablesat 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 tablesat 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;
其他关于@ManyToMany(多对多关系)的使用可以去百度再看看，本人就不多说了。
再见！