ManyToMany单向和双向@JoinTable的使用方法是什么
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ManyToMany单向、双向:@JoinTable使用
一、manytomany单向
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
@Entitypublic 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 s=new HashSet(); @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 getS() { return s; } public void setS(Set s) { this.s = s; } } 二、manytomany双向
也可以用@JoinTable对连接表字段名进行修改
@Entitypublic class student { private int id; private String name; private Set ts=new HashSet(); @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 getTs() { return ts; } public void setTs(Set ts) { this.ts = ts; }} @Entity public class teacher { private int id; private String name; private Set s=new HashSet(); @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 getS() { return s; } public void setS(Set s) { this.s = s; }} @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 elementList; public List getElementList() { return elementList; } public void setElementList(List 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 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，小编将为大家推送更多相关知识点的文章，欢迎关注！
