如何在Java / IntelliJ中创建从一个类到另一个类的一对多和多对一关系

时间：2017-11-16 20:27:11

标签： java hibernate jpa intellij-idea one-to-many

我已经研究过如何解决这个问题，但没有一个对我有用。我知道我不完全理解它是如何工作的 - 这正是重点，但有时我必须停下来寻求帮助/澄清。

我正在从事一个侧面项目（并且正在研究我的编程技巧）。请注意，我是初中级别。

我正在尝试创建两个类，其中一个类具有多个一对一关系的字段。只有两个字段具有1到M的关系和M到M的关系。 “Dog”类有一个名为picture的字段，它与“Picture”类是1到M的关系。对于我的生活，每次我执行代码 - 它都会遇到问题。我已经尝试了几种方法使其工作 - 例如使类可序列化，使一个字段由另一个映射，反之亦然，使用CascadeType等等。我已经意识到也许我不太明白它在Java中是如何工作的（我正在使用IntelliJ），尽管我理解它的概念。

我读过并尝试过的文章仅举几例：

Entity Framework one-to-many and many-to-many relationship

Multiple 1:many relationship in Hibernate

Java JPA one to many

http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html_single/#entity-mapping-association

Hibernate One to Many and Many to One Relation

我有一种感觉，我真的很接近我想做的事情......但我似乎忽略了一些事情，非常。

我的数据库的意图：

我正在Dog表中的每一行都有自己的名字，重量等。 每行（狗）将分配许多图片。它们将以数据库中的URL地址的形式出现，我打算使用spring框架调用它。我找到了Cloudinary，并认为我可以尝试用我的代码来实现它们。我的这个侧面项目是改善现有的，工作实验室救援组织，它拥有我见过的最基本的网站。

以下是我的代码：

狗桌/班级 

package com.claudiazeledon.LuckyLabsRescue.models;

import org.hibernate.annotations.Target;

import javax.persistence.*;
import java.io.Serializable;
import java.util.Collection;
import java.util.Set;

@Entity
public class Dog{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column
    private String name;

    @Column
    private Integer weight;

    @Column
    private Integer age;

    @Column
    private Gender gender;

    @Column
    private String color;

    @OneToOne
    private Temperament temperament;

    @OneToOne
    private Availability availability;

    @OneToOne
    private Health health;

    @OneToMany
    @JoinColumn(name = "picture_dp")
    private Set<Picture> getPictures;

    public Dog() {
    }

    public Dog(int id, String name, Integer weight, Integer age, Gender gender, String color, Temperament temperament, Availability availability, Health health, Set<Picture> getPictures) {
        this.id = id;
        this.name = name;
        this.weight = weight;
        this.age = age;
        this.gender = gender;
        this.color = color;
        this.temperament = temperament;
        this.availability = availability;
        this.health = health;
        this.getPictures = getPictures;
    }

    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;
    }

    public Integer getWeight() {
        return weight;
    }

    public void setWeight(Integer weight) {
        this.weight = weight;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Gender getGender() {
        return gender;
    }

    public void setGender(Gender gender) {
        this.gender = gender;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public Temperament getTemperament() {
        return temperament;
    }

    public void setTemperament(Temperament temperament) {
        this.temperament = temperament;
    }

    public Availability getAvailability() {
        return availability;
    }

    public void setAvailability(Availability availability) {
        this.availability = availability;
    }

    public Health getHealth() {
        return health;
    }

    public void setHealth(Health health) {
        this.health = health;
    }

    public Set<Picture> getGetPictures() {
        return getPictures;
    }

    public void setGetPictures(Set<Picture> getPictures) {
        this.getPictures = getPictures;
    }
}

图片表/类 

package com.claudiazeledon.LuckyLabsRescue.models;

import javax.persistence.*;
import java.net.URL;

@Entity
@Table(name = "picture")
public class Picture{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @ManyToOne
    @JoinColumn(name = "picture_dp", insertable = false, updatable = false)
    private URL pictureURL;

//    @ManyToOne
//    @JoinColumn(name = "pictureId")
//    @MapsId("pictureId")
//    private Dog dogImage;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public URL getPictureURL() {
        return pictureURL;
    }

    public void setPictureURL(URL pictureURL) {
        this.pictureURL = pictureURL;
    }

}

IntelliJ的错误消息 

2017-11-16 15:20:35.300  INFO 24180 --- [  restartedMain] org.hibernate.Version                    : HHH000412: Hibernate Core {5.0.12.Final}
2017-11-16 15:20:35.301  INFO 24180 --- [  restartedMain] org.hibernate.cfg.Environment            : HHH000206: hibernate.properties not found
2017-11-16 15:20:35.302  INFO 24180 --- [  restartedMain] org.hibernate.cfg.Environment            : HHH000021: Bytecode provider name : javassist
2017-11-16 15:20:35.418  INFO 24180 --- [  restartedMain] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.0.1.Final}
2017-11-16 15:20:35.518  INFO 24180 --- [  restartedMain] org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
2017-11-16 15:20:35.623  INFO 24180 --- [  restartedMain] o.h.e.j.e.i.LobCreatorBuilderImpl        : HHH000424: Disabling contextual LOB creation as createClob() method threw error : java.lang.reflect.InvocationTargetException
2017-11-16 15:20:35.625  INFO 24180 --- [  restartedMain] org.hibernate.type.BasicTypeRegistry     : HHH000270: Type registration [java.util.UUID] overrides previous : org.hibernate.type.UUIDBinaryType@673c77b3
2017-11-16 15:20:35.766  WARN 24180 --- [  restartedMain] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaAutoConfiguration.class]: Invocation of init method failed; nested exception is org.hibernate.AnnotationException: @OneToOne or @ManyToOne on com.claudiazeledon.LuckyLabsRescue.models.Picture.pictureURL references an unknown entity: java.net.URL
2017-11-16 15:20:35.771  INFO 24180 --- [  restartedMain] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
2017-11-16 15:20:35.782  INFO 24180 --- [  restartedMain] utoConfigurationReportLoggingInitializer : 

Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2017-11-16 15:20:35.792 ERROR 24180 --- [  restartedMain] o.s.boot.SpringApplication               : Application startup failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaAutoConfiguration.class]: Invocation of init method failed; nested exception is org.hibernate.AnnotationException: @OneToOne or @ManyToOne on com.claudiazeledon.LuckyLabsRescue.models.Picture.pictureURL references an unknown entity: java.net.URL
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1628) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1078) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:857) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at com.claudiazeledon.LuckyLabsRescue.LuckyLabsRescueApplication.main(LuckyLabsRescueApplication.java:10) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_144]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_144]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_144]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_144]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-1.5.8.RELEASE.jar:1.5.8.RELEASE]
Caused by: org.hibernate.AnnotationException: @OneToOne or @ManyToOne on com.claudiazeledon.LuckyLabsRescue.models.Picture.pictureURL references an unknown entity: java.net.URL
    at org.hibernate.cfg.ToOneFkSecondPass.doSecondPass(ToOneFkSecondPass.java:97) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processEndOfQueue(InFlightMetadataCollectorImpl.java:1786) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processFkSecondPassesInOrder(InFlightMetadataCollectorImpl.java:1730) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1617) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:278) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:847) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:874) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:60) ~[spring-orm-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:353) ~[spring-orm-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:370) ~[spring-orm-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:359) ~[spring-orm-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1687) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1624) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    ... 21 common frames omitted

2 个答案:

答案 0 :(得分：0)

您在-Swift.h上建立了@ManyToOne关系：

pictureUrl

实体之间建立了关系，但URL不是实体。

最简单的解决方案是删除该字段上的@ManyToOne @JoinColumn(name = "picture_dp", insertable = false, updatable = false) private URL pictureURL; 和@ManyToOne注释，并使用常规@JoinColumn注释替换它们。

@Column

答案 1 :(得分：0)

只看这个例子。您对一对多关系的疑问将显而易见。例如拿2个实体。 CustomerEntity.java和ProductEntity.java。在CustomerEntity.java中添加

@OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "customer") private Product product;

并在ProductEntity.java中添加字段。

@ManyToOne(fetch = FetchType.LAZY, optional = false) @JoinColumn(name = "customer_id", nullable = false) @JsonIgnore private Customer customer;

在实体类中同时对字段和implements Serializable接口进行

getter setter设置。如果您使用的是json数据类型，则可以添加@JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })

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