In this post, I am going to explain how to define a composite key using entity associations.
For example, a book primary key is defined with
a. Book title
b. Author id
c. Publisher Id
Example
@Entity
@Table(name = "book")
public class Book {
@Id
private String title;
@Id
@ManyToOne(fetch = FetchType.LAZY)
private Author author;
@Id
@ManyToOne(fetch = FetchType.LAZY)
private Publisher publisher;
...........
...........
}
@Entity
@Table(name = "author")
public class Author {
@Id
private Integer authorId;
private String name;
..........
..........
}
@Entity
@Table(name = "publisher")
public class Publisher {
@Id
private Integer publisherId;
private String name;
..........
..........
}
Find the below working application.
Step 1: Create new maven project ‘hibernate-composite-id-with-associations’.
Step 2: Update pom.xml with maven dependencies.
pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.sample.app</groupId>
<artifactId>hibernate-composite-id-with-associations</artifactId>
<version>1</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<java.version>15</java.version>
<maven.compiler.source>${java.version}</maven.compiler.source>
<maven.compiler.target>${java.version}</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>42.4.1</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>6.1.2.Final</version>
</dependency>
</dependencies>
</project>
Step 3: Define entity classes.
Author.java
package com.sample.app.entity;
import java.util.Objects;
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
@Entity
@Table(name = "author")
public class Author {
@Id
private Integer authorId;
private String name;
public Author(Integer authorId, String name) {
this.authorId = authorId;
this.name = name;
}
public Integer getAuthorId() {
return authorId;
}
public void setAuthorId(Integer authorId) {
this.authorId = authorId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Author [empId=" + authorId + ", name=" + name + "]";
}
@Override
public int hashCode() {
return Objects.hash(authorId, name);
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Author other = (Author) obj;
return Objects.equals(authorId, other.authorId) && Objects.equals(name, other.name);
}
}
Publisher.java
package com.sample.app.entity;
import java.util.Objects;
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
@Entity
@Table(name = "publisher")
public class Publisher {
@Id
private Integer publisherId;
private String name;
public Publisher(Integer publisherId, String name) {
this.publisherId = publisherId;
this.name = name;
}
public Integer getPublisherId() {
return publisherId;
}
public void setPublisherId(Integer publisherId) {
this.publisherId = publisherId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Publisher [publisherId=" + publisherId + ", name=" + name + "]";
}
@Override
public int hashCode() {
return Objects.hash(name, publisherId);
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Publisher other = (Publisher) obj;
return Objects.equals(name, other.name) && Objects.equals(publisherId, other.publisherId);
}
}
Book.java
package com.sample.app.entity;
import jakarta.persistence.Entity;
import jakarta.persistence.FetchType;
import jakarta.persistence.Id;
import jakarta.persistence.ManyToOne;
import jakarta.persistence.Table;
@Entity
@Table(name = "book")
public class Book {
@Id
private String title;
@Id
@ManyToOne(fetch = FetchType.LAZY)
private Author author;
@Id
@ManyToOne(fetch = FetchType.LAZY)
private Publisher publisher;
public Book() {}
public Book(String title, Author author, Publisher publisher) {
this.title = title;
this.author = author;
this.publisher = publisher;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public Author getAuthor() {
return author;
}
public void setAuthor(Author author) {
this.author = author;
}
public Publisher getPublisher() {
return publisher;
}
public void setPublisher(Publisher publisher) {
this.publisher = publisher;
}
@Override
public String toString() {
return "Book [title=" + title + "]";
}
}
Step 4: Create hibernate.cfg.xml file under src/main/resources folder.
hibernate.cfg.xml
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database Connection settings -->
<property name="connection.driver_class">org.postgresql.Driver</property>
<property name="connection.url">jdbc:postgresql://127.0.0.1:5432/test</property>
<property name="connection.username">postgres</property>
<property name="connection.password">postgres</property>
<!-- Enable the logging of all the generated SQL statements to the console -->
<property name="show_sql">true</property>
<!-- Format the generated SQL statement to make it more readable, -->
<property name="format_sql">false</property>
<!-- Hibernate will put comments inside all generated SQL statements to
hint what’s the generated SQL trying to do -->
<property name="use_sql_comments">false</property>
<!-- This property makes Hibernate generate the appropriate SQL for the
chosen database. -->
<property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">create</property>
<!-- mappings for annotated classes -->
<mapping class="com.sample.app.entity.Author" />
<mapping class="com.sample.app.entity.Publisher" />
<mapping class="com.sample.app.entity.Book" />
</session-factory>
</hibernate-configuration>
Step 5: Define main application class.
App.java
package com.sample.app;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import com.sample.app.entity.Author;
import com.sample.app.entity.Book;
import com.sample.app.entity.Publisher;
import jakarta.persistence.criteria.CriteriaBuilder;
import jakarta.persistence.criteria.CriteriaQuery;
public class App {
private static SessionFactory sessionFactory = buildSessionFactory();
private static <T> List<T> loadAllData(Class<T> clazz, Session session) {
final CriteriaBuilder builder = session.getCriteriaBuilder();
final CriteriaQuery<T> criteria = builder.createQuery(clazz);
criteria.from(clazz);
return session.createQuery(criteria).getResultList();
}
private static SessionFactory buildSessionFactory() {
try {
if (sessionFactory == null) {
StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder()
.configure("hibernate.cfg.xml").build();
Metadata metaData = new MetadataSources(standardRegistry).getMetadataBuilder().build();
sessionFactory = metaData.getSessionFactoryBuilder().build();
}
return sessionFactory;
} catch (Throwable ex) {
throw new ExceptionInInitializerError(ex);
}
}
public static void main(String args[]) {
Author author1 = new Author(1, "Krishna");
Publisher publisher1 = new Publisher(1, "blogger");
try (Session session = sessionFactory.openSession()) {
session.beginTransaction();
session.persist(author1);
session.persist(publisher1);
session.flush();
session.getTransaction().commit();
Author persistedAuthor = session.find(Author.class, 1);
Publisher persistedPublisher = session.find(Publisher.class, 1);
session.beginTransaction();
Book book = new Book("Programming for beginners", persistedAuthor, persistedPublisher);
session.persist(book);
session.flush();
session.getTransaction().commit();
List<Book> books = loadAllData(Book.class, session);
for (Book book1 : books) {
System.out.println(book1);
System.out.println(book1.getAuthor());
System.out.println(book1.getPublisher());
}
}
}
}
Total project structure looks like below.
Run App.java, you will see below messages in the console.
Sep 05, 2022 4:50:32 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 6.1.2.Final
Sep 05, 2022 4:50:32 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using built-in connection pool (not intended for production use)
Sep 05, 2022 4:50:32 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: Loaded JDBC driver class: org.postgresql.Driver
Sep 05, 2022 4:50:32 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001012: Connecting with JDBC URL [jdbc:postgresql://127.0.0.1:5432/test]
Sep 05, 2022 4:50:32 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=postgres}
Sep 05, 2022 4:50:32 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Sep 05, 2022 4:50:32 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH10001115: Connection pool size: 20 (min=1)
Sep 05, 2022 4:50:32 PM org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl logSelectedDialect
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
Sep 05, 2022 4:50:32 PM org.hibernate.mapping.RootClass checkCompositeIdentifier
WARN: HHH000038: Composite-id class does not override equals(): com.sample.app.entity.Book
Sep 05, 2022 4:50:32 PM org.hibernate.mapping.RootClass checkCompositeIdentifier
WARN: HHH000039: Composite-id class does not override hashCode(): com.sample.app.entity.Book
Sep 05, 2022 4:50:33 PM org.hibernate.metamodel.internal.EntityInstantiatorPojoStandard resolveConstructor
INFO: HHH000182: No default (no-argument) constructor for class: com.sample.app.entity.Author (class must be instantiated by Interceptor)
Sep 05, 2022 4:50:33 PM org.hibernate.metamodel.internal.EntityInstantiatorPojoStandard resolveConstructor
INFO: HHH000182: No default (no-argument) constructor for class: com.sample.app.entity.Publisher (class must be instantiated by Interceptor)
Hibernate: alter table if exists book drop constraint if exists FKphbqlkautxpp937p1gshnxcqv
Sep 05, 2022 4:50:33 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@4d3c6593] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: relation "book" does not exist, skipping
Hibernate: alter table if exists book drop constraint if exists FKektypek2eiyeyfigr8kvudw9m
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: relation "book" does not exist, skipping
Hibernate: drop table if exists author cascade
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: table "author" does not exist, skipping
Hibernate: drop table if exists book cascade
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: table "book" does not exist, skipping
Hibernate: drop table if exists publisher cascade
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Sep 05, 2022 4:50:33 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: table "publisher" does not exist, skipping
Hibernate: create table author (authorId integer not null, name varchar(255), primary key (authorId))
Sep 05, 2022 4:50:33 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@54755dd9] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: create table book (title varchar(255) not null, publisher_publisherId integer not null, author_authorId integer not null, primary key (author_authorId, publisher_publisherId, title))
Hibernate: create table publisher (publisherId integer not null, name varchar(255), primary key (publisherId))
Hibernate: alter table if exists book add constraint FKphbqlkautxpp937p1gshnxcqv foreign key (publisher_publisherId) references publisher
Hibernate: alter table if exists book add constraint FKektypek2eiyeyfigr8kvudw9m foreign key (author_authorId) references author
Sep 05, 2022 4:50:33 PM org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformInitiator initiateService
INFO: HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
Hibernate: insert into author (name, authorId) values (?, ?)
Hibernate: insert into publisher (name, publisherId) values (?, ?)
Hibernate: insert into book (author_authorId, publisher_publisherId, title) values (?, ?, ?)
Hibernate: select b1_0.author_authorId,b1_0.publisher_publisherId,b1_0.title from book b1_0
Book [title=Programming for beginners]
Author [empId=1, name=Krishna]
Publisher [publisherId=1, name=blogger]
Query PostgreSQL database for the DDL.
test=# \d+ author
Table "public.author"
Column | Type | Collation | Nullable | Default | Storage | Compression | Stats target | Description
----------+------------------------+-----------+----------+---------+----------+-------------+--------------+-------------
authorid | integer | | not null | | plain | | |
name | character varying(255) | | | | extended | | |
Indexes:
"author_pkey" PRIMARY KEY, btree (authorid)
Referenced by:
TABLE "book" CONSTRAINT "fkektypek2eiyeyfigr8kvudw9m" FOREIGN KEY (author_authorid) REFERENCES author(authorid)
Access method: heap
test=#
test=#
test=# \d+ publisher
Table "public.publisher"
Column | Type | Collation | Nullable | Default | Storage | Compression | Stats target | Description
-------------+------------------------+-----------+----------+---------+----------+-------------+--------------+-------------
publisherid | integer | | not null | | plain | | |
name | character varying(255) | | | | extended | | |
Indexes:
"publisher_pkey" PRIMARY KEY, btree (publisherid)
Referenced by:
TABLE "book" CONSTRAINT "fkphbqlkautxpp937p1gshnxcqv" FOREIGN KEY (publisher_publisherid) REFERENCES publisher(publisherid)
Access method: heap
test=#
test=#
test=# \d+ book
Table "public.book"
Column | Type | Collation | Nullable | Default | Storage | Compression | Stats target | Description
-----------------------+------------------------+-----------+----------+---------+----------+-------------+--------------+-------------
title | character varying(255) | | not null | | extended | | |
publisher_publisherid | integer | | not null | | plain | | |
author_authorid | integer | | not null | | plain | | |
Indexes:
"book_pkey" PRIMARY KEY, btree (author_authorid, publisher_publisherid, title)
Foreign-key constraints:
"fkektypek2eiyeyfigr8kvudw9m" FOREIGN KEY (author_authorid) REFERENCES author(authorid)
"fkphbqlkautxpp937p1gshnxcqv" FOREIGN KEY (publisher_publisherid) REFERENCES publisher(publisherid)
Access method: heap
You can download this application from this link.
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