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ManyToMany单向、双向:@JoinTable的使用_java

longge3个月前 (03-01)网络技术72
目录
  • ManyToMany单向、双向:@JoinTable使用
    • 一、manytomany单向
    • 二、manytomany双向
  • @ManyToMany(多对多关系)使用小结

    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

    @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;
        }   
    }
    

    二、manytomany双向

    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;
        }
    }
    

    @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 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;

    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。

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