JPA中三个实体之间的一对多映射答案

【问题标题】：One to Many mapping between three entities in JPAJPA中三个实体之间的一对多映射
【发布时间】：2016-06-20 09:31:22
【问题描述】：

我想在三个实体之间建立多对一关系，即用户到板（多）和板到卡（多），即一个用户可以有很多板，一个板可以有很多卡。我正在使用 Spring JPA 并自动创建数据库模式。我已经正确设置了属性，但我无法正确连接它们，以便可以自动构建 db 架构。这是我的模型类，请帮助：-

@Entity
@Table(name = "user")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "userid")
    private Long id;

    @Column(name = "username")
    private String username;

    @Column(name = "password")
    private String password;

    @OneToMany(fetch =  FetchType.LAZY ,mappedBy = "username" , targetEntity = Board.class)
    private List<Board> boards;

}

板级

@Entity
@Table(name = "board")
public class Board {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "boardid")
    private Long id;

    @Column(name = "boardname")
    private String boardname;

    @Column(name = "boardcreationdate")
    private DateTime boardCreationDate;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "userid", referencedColumnName = "userid")
    private User username;

    @OneToMany(fetch =  FetchType.LAZY ,mappedBy = "boardname" , targetEntity = Board.class)
    private Set<Card> cards;

}

卡类

@Entity
@Table(name = "card")
public class Card {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "cardid")
    private Long id;

    @Column(name = "cardName")
    private String cardName;

    @Column(name = "cardcreationdate")
    private DateTime cardCreationDate;

    @Column(name = "cardtimeondone")
    private DateTime cardTimeOnDone;

    @Column(name = "cardlife")
    private DateTime cardLife;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "boardid", referencedColumnName = "boardid")
    private Board boardname;

}

这是包含一些属性的 application.properties 文件。

spring.datasource.initialize=true
spring.datasource.platform=mysql
spring.datasource.time-between-eviction-runs-millis=34000
spring.datasource.min-evictable-idle-time-millis=55000
spring.datasource.max-wait=28800000
spring.jpa.generate-ddl=true
spring.jpa.hibernate.ddl-auto=create
spring.jpa.properties.hibernate.dialect =org.hibernate.dialect.MySQL5Dialect
spring.jpa.properties.hibernate.format_sql=true

它正在创建架构，但出现如下错误：-

        2016-06-20 15:12:37.288 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    alter table board 
        drop 
        foreign key FKbon6omt9qov9iduumkuj117xw
2016-06-20 15:12:37.357 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    alter table board 
        drop 
        foreign key FKcefyg893q4c26nvw7uus84ts3
2016-06-20 15:12:37.386  WARN 8772 --- [           main] o.h.t.s.i.ExceptionHandlerLoggedImpl     : GenerationTarget encountered exception accepting command : Unable to execute command [
    alter table board 
        drop 
        foreign key FKcefyg893q4c26nvw7uus84ts3]

org.hibernate.tool.schema.spi.CommandAcceptanceException: Unable to execute command [
    alter table board 
        drop 
        foreign key FKcefyg893q4c26nvw7uus84ts3]
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:63) ~[hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.applySqlString(SchemaDropperImpl.java:370) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.applySqlStrings(SchemaDropperImpl.java:355) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.applyConstraintDropping(SchemaDropperImpl.java:327) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.dropFromMetadata(SchemaDropperImpl.java:229) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.performDrop(SchemaDropperImpl.java:153) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.doDrop(SchemaDropperImpl.java:125) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.doDrop(SchemaDropperImpl.java:111) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:137) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:64) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:458) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:465) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:881) [hibernate-entitymanager-5.1.0.Final.jar:5.1.0.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:60) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:338) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:373) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:362) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1637) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1574) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1076) [spring-context-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:851) [spring-context-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541) [spring-context-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:765) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:370) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:314) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1182) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1171) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at com.causecode.challenge.TrellocardlifeApplication.main(TrellocardlifeApplication.java:14) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_25]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_25]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_25]
    at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_25]
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144) [idea_rt.jar:na]
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Can't DROP 'FKcefyg893q4c26nvw7uus84ts3'; check that column/key exists
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_25]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_25]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_25]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408) ~[na:1.8.0_25]
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.Util.getInstance(Util.java:381) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1030) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:734) ~[mysql-connector-java-5.1.6.jar:na]
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:51) ~[hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    ... 38 common frames omitted

2016-06-20 15:12:37.392 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    alter table card 
        drop 
        foreign key FKgicrq63fj0nx3bh6wlncf235i
2016-06-20 15:12:37.424 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    drop table if exists board
2016-06-20 15:12:37.437 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    drop table if exists card
2016-06-20 15:12:37.448 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    drop table if exists user
2016-06-20 15:12:37.468 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    create table board (
        boardid bigint not null auto_increment,
        boardcreationdate tinyblob,
        boardname varchar(255),
        userid bigint,
        primary key (boardid)
    )
2016-06-20 15:12:37.539 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    create table card (
        id bigint not null auto_increment,
        cardcreationdate tinyblob,
        cardlife tinyblob,
        card_name varchar(255),
        cardtimeondone tinyblob,
        boardid bigint,
        primary key (id)
    )
2016-06-20 15:12:37.600 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    create table user (
        userid bigint not null auto_increment,
        password varchar(255),
        username varchar(255),
        primary key (userid)
    )
2016-06-20 15:12:37.631 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    alter table board 
        add constraint FKbon6omt9qov9iduumkuj117xw 
        foreign key (userid) 
        references user (userid)
2016-06-20 15:12:37.752 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    alter table board 
        add constraint FKcefyg893q4c26nvw7uus84ts3 
        foreign key (boardname) 
        references board (boardid)
2016-06-20 15:12:37.812  WARN 8772 --- [           main] o.h.t.s.i.ExceptionHandlerLoggedImpl     : GenerationTarget encountered exception accepting command : Unable to execute command [
    alter table board 
        add constraint FKcefyg893q4c26nvw7uus84ts3 
        foreign key (boardname) 
        references board (boardid)]

org.hibernate.tool.schema.spi.CommandAcceptanceException: Unable to execute command [
    alter table board 
        add constraint FKcefyg893q4c26nvw7uus84ts3 
        foreign key (boardname) 
        references board (boardid)]
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:63) ~[hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.applySqlString(SchemaCreatorImpl.java:423) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.applySqlStrings(SchemaCreatorImpl.java:408) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.createFromMetadata(SchemaCreatorImpl.java:359) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.performCreation(SchemaCreatorImpl.java:165) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.doCreation(SchemaCreatorImpl.java:134) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.internal.SchemaCreatorImpl.doCreation(SchemaCreatorImpl.java:120) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:148) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:64) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:458) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:465) [hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:881) [hibernate-entitymanager-5.1.0.Final.jar:5.1.0.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:60) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:338) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:373) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:362) [spring-orm-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1637) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1574) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) [spring-beans-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1076) [spring-context-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:851) [spring-context-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541) [spring-context-4.3.0.RC2.jar:4.3.0.RC2]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:765) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:370) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:314) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1182) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1171) [spring-boot-1.4.0.M3.jar:1.4.0.M3]
    at com.causecode.challenge.TrellocardlifeApplication.main(TrellocardlifeApplication.java:14) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_25]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_25]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_25]
    at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_25]
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144) [idea_rt.jar:na]
Caused by: java.sql.SQLException: Cannot add foreign key constraint
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465) ~[mysql-connector-java-5.1.6.jar:na]
    at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:734) ~[mysql-connector-java-5.1.6.jar:na]
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:51) ~[hibernate-core-5.1.0.Final.jar:5.1.0.Final]
    ... 37 common frames omitted

2016-06-20 15:12:37.814 DEBUG 8772 --- [           main] org.hibernate.SQL                        : 
    alter table card 
        add constraint FKgicrq63fj0nx3bh6wlncf235i 
        foreign key (boardid) 
        references board (boardid)
2016-06-20 15:12:37.900  INFO 8772 --- [           main] o.h.t.schema.internal.SchemaCreatorImpl  : HHH000476: Executing import script 'org.hibernate.tool.schema.internal.exec.ScriptSourceInputNonExistentImpl@329bad59'
2016-06-20 15:12:37.954  INFO 8772 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
2016-06-20 15:12:39.191  INFO 8772 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2016-06-20 15:12:39.200  INFO 8772 --- [           main] o.s.c.support.DefaultLifecycleProcessor  : Starting beans in phase 0
2016-06-20 15:12:39.305  INFO 8772 --- [           main] c.c.challenge.TrellocardlifeApplication  : Started TrellocardlifeApplication in 8.172 seconds (JVM running for 8.914)
2016-06-20 15:12:39.306  INFO 8772 --- [       Thread-3] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@7fad8c79: startup date [Mon Jun 20 15:12:31 IST 2016]; root of context hierarchy
2016-06-20 15:12:39.308  INFO 8772 --- [       Thread-3] o.s.c.support.DefaultLifecycleProcessor  : Stopping beans in phase 0
2016-06-20 15:12:39.310  INFO 8772 --- [       Thread-3] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown
2016-06-20 15:12:39.310  INFO 8772 --- [       Thread-3] j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'default'

Process finished with exit code 0

我认为只有实体类有问题。请帮我定义一个正确的模型并在 mysql 中自动创建它们。

【问题讨论】：

如果有人能告诉我这个映射的正确数据库模式应该是什么。一种方式一对多和双向多对一映射。

标签： java mysql jpa spring-boot

【解决方案1】：

尝试这样改变：

@Entity
@Table(name = "user")
public class User {
  @OneToMany(mappedBy = "user")
  private List<Board> boards;

}

@Entity
@Table(name = "board")
public class Board {
    @ManyToOne(cascade=CascadeType.PERSIST)
    @JoinColumn(name = "userid")
    private User user;

    @OneToMany(mappedBy = "board")
    private Set<Card> cards;
}

@Entity
@Table(name = "card")
public class Card {

    @ManyToOne(cascade=CascadeType.PERSIST)
    @JoinColumn(name = "boardid")
    private Board board;

}

【讨论】：

Bhashkar .. 我也尝试根据您的方法映射实体，但只有 3 个表.. 即用户 (userid, password, username) , Board (boardid, boardcreationdate, boardname, userid ), Card (cardid, cardcreationdate, cardlife, cardtimeondone, cardname, boardid) .. 我有一个问题，在 board 和 user 表中没有 board 和 cards 的集合列。 ..你能告诉我什么应该是正确的架构。 ..会很有帮助的..
@hjain25 这是正确的模式 :) 作为经验法则，请记住在 1 到 M 关系中，1 侧的主键作为（外键）列进入多方。这就是为什么您在Card 中看到boardid 和在Board 中看到userid 的原因。这些集合实际上是虚拟的，hibernate 根据外键将多方提取到这个集合中。所以请使用 Anil 的方法 ?? 请阅读更多关于如何在 JPA/Hibernate 中解决关系的信息。这是一次性的任务——一旦你理解了它，你就不会忘记你的余生:)
@hjain25 它不会在User 表中创建一个列，其中包含数据库中的Board 值列表。尽管User 的java 对象将拥有与之关联的所有Board 对象。
@hjain25 如果解决了您的问题，请接受答案。

【解决方案2】：

不确定这是否能解决您的错误，但这看起来无效

 @OneToMany(fetch =  FetchType.LAZY ,mappedBy = "boardname" , targetEntity = Board.class)
    private Set<Card> cards;

应该是

 @OneToMany(fetch =  FetchType.LAZY ,mappedBy = "boardname" , targetEntity = Card.class)
    private Set<Card> cards;

【讨论】：

@hjain25 检查 Boards.java 中 Card 的导入语句。您似乎导入了javax.smartcardio.Card。您需要将其替换为 Card 实体的正确路径
是的，我发现了我的这个愚蠢的错误并更正了，但是......我也想确定 DB 模式 .. 它正在创建这样的模式。板（boardid，boardcreationdate，boardname，userid），board_cards（board_boardid，cards_id），Card（cardid，cardcreationdate，cardlife，cardtimeondone，cardname，boardid），用户（userid，密码，用户名），user_boards（user_userid，boards_boardid）..我不确定它为什么要创建一个单独的模式来链接两个实体的 id，因为多对多映射就是这种情况。请评论。谢谢。
嗯，是的，架构看起来不正确。它不应该生成中间表。这意味着您的注释在某处不正确。试试这个 - 从所有 @JoinColumn 注释中删除 referencedColumnName。也可以试试上面 Anil 的方法——它看起来很简洁。
,.. 我尝试删除 referencedColumnName 这并没有改变架构中的任何内容。 ..我也尝试根据Anil的方法映射实体，但只有3个表..即用户（用户ID，密码，用户名），董事会（boardid，boardcreationdate，boardname，userid），Card（cardid，cardcreationdate， cardlife, cardtimeondone, cardname, boardid) .. 我有一个问题，在 board 和 user 表中没有用于 board 和 cards 的集合列的列。 ..你能告诉我什么应该是正确的架构。 ..会很有帮助的..