How to create One-to-Many and Many-to-One Relationship from one class to another class in Java/IntelliJ

Question

I've done research on how to resolve this issue and none of it worked for me. I know I don't fully understand how it works--which is exactly the point, but sometimes I have to stop and ask for help/clarification.

I am working on a side project (and working on my programming skills). Please note, I am on a junior level.

I am trying to create two classes where one class has several fields that is one to one relationship. There are only two fields that will have 1 to M relationship and M to M relationship. The "Dog" class has a field called picture which will be 1 to M relationship with a "Picture" class. For the life of me, every time I execute the code--it runs into problems. I've tried several ways to make it work-- such as making the class serializable, having one field mapped by another and vice versa, used the CascadeType and many more. I've come to realize perhaps I don't quite understand how it works in Java (I am using IntelliJ), even though I understood the concept of it.

The articles I've read and tried using to name a few:

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

I have a feeling that I was really close to what I was trying to do...but I seem to overlook something, badly.

The intention of my database:

I'm making each row in the Dog table that has their own name, weight, etc. Each row (dog) will have many pictures assigned to them. They will be in the form of URL address in the database which I plan to call on it using spring framework. I found Cloudinary and figured I can try to implement their code with mine. This side project of mine is to improve a current, working lab rescue organization that has the most basic website I've ever seen.

Here are my codes:

Dog Table/Class

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;
    }
}

Picture Table/Class

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;
    }

}

Error Message from IntelliJ

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

score 1 · Answer 1 · answered Nov 02 '19 at 10:55

Just look at this example. Your doubt to one to many relation will be clear. For example take 2 entities. CustomerEntity.java and ProductEntity.java. In CustomerEntity.java add

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

and add field in ProductEntity.java.

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

make getter setter of both field and implements Serializable interface in Entity class. If you are using json data type then you can add @JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })

ESala · Accepted Answer · 2017-11-16T21:58:14.960

0

You put a @ManyToOne relationship on the pictureUrl:

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

Relationships are established between entities, but URL is not an entity.

The easiest solution is to remove the @ManyToOne and @JoinColumn annotations on that field an replace them with a regular @Column annotation.

@Column
private URL pictureURL;

edited Nov 16 '17 at 21:58

answered Nov 16 '17 at 20:41

ESala

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Oh my! That works! However, I find myself wondering if it will successfully assign the pictureURL to the primary id in the dog table? – Claudia Nov 16 '17 at 21:50
@Claudia yes, your `Dog` entity will be linked to several `Picture` entities, because you used the `@ManyToOne` annotation in the `Dog` class. The `pictureUrl` will also be linked because it is inside the `Picture` class. Just make sure to put a regular `@Column` annotation on it. Remember to accept the answer if it solved your problem :) – ESala Nov 16 '17 at 21:57
Ah, I was supposed to use `@ManyToOne` instead of `@OneToMany` annotation in the `Dog` class? I thought `@OneToMany` means that one dog will have many photos, not the other way around. I will definitely accept once my issue is resolved! I'm testing this now. – Claudia Nov 17 '17 at 01:32
@Claudia when thinking about these annotations, the first term refers to the class and the second to the field. Example: `@ManyToOne` on a `picture` field inside `Dog` class means: many-dogs to one-picture. In your `Dog` class you have a `@OneToMany` annotation on the picture, so that means: one-dog to many-pictures, which I think is what you want. – ESala Nov 17 '17 at 08:28

How to create One-to-Many and Many-to-One Relationship from one class to another class in Java/IntelliJ

2 Answers2