Entity identifiers are used to uniquely identify a row in a table. Hibernate and JPA (Jakarta Persistence API), assumes following rules must be followed by the identifier.
a. Identifier must be unique in a table.
b. Identifier must not be null. If you use a composite key as an identifier, then no other part can be null.
c. Once a value assigned to identifier property, the value must not be changed on any circumstances.
Types of identifiers
An identifier can be
a. Simple
b. Composite
Let’s discuss how to model a composite identifier using @EmbeddedId annotation.
Step 1: Define an embeddable class. As per the documentation, the primary key class must be serializable.
@Embeddable
public class EmployeePK implements Serializable {
private int empId;
private int deptId;
........
........
}
Step 2: Model the variable of EmployeePK as primary key in the actual Employee entity class.
@Entity
@Table(name = "employees")
public class Employee {
@EmbeddedId
private EmployeePK empPK;
..........
..........
}
Find the below working application.
Step 1: Create new maven project ‘hibernate-composite-id-by-embedded-id’.
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-by-embedded-id</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: Model Employee entity class.
EmployeePK.java
package com.sample.app.entity;
import java.io.Serializable;
import jakarta.persistence.Embeddable;
@Embeddable
public class EmployeePK implements Serializable {
private int empId;
private int deptId;
public int getEmpId() {
return empId;
}
public void setEmpId(int empId) {
this.empId = empId;
}
public int getDeptId() {
return deptId;
}
public void setDeptId(int deptId) {
this.deptId = deptId;
}
@Override
public String toString() {
return "EmployeePK [empId=" + empId + ", deptId=" + deptId + "]";
}
}
Employee.java
package com.sample.app.entity;
import jakarta.persistence.EmbeddedId;
import jakarta.persistence.Entity;
import jakarta.persistence.Table;
@Entity
@Table(name = "employees")
public class Employee {
@EmbeddedId
private EmployeePK empPK;
private String firstName;
private String lastName;
public EmployeePK getEmpPK() {
return empPK;
}
public void setEmpPK(EmployeePK empPK) {
this.empPK = empPK;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
@Override
public String toString() {
return "Employee [empPK=" + empPK + ", firstName=" + firstName + ", lastName=" + lastName + "]";
}
}
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">true</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.Employee" />
</session-factory>
</hibernate-configuration>
Step 5: Define main application class.
App.java
package com.sample.app;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
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.Employee;
import com.sample.app.entity.EmployeePK;
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[]) {
Map<String, Object> config = new HashMap<>();
config.put("maxThreads", 10);
config.put("storagePath", "/Users/krishna/my-docs");
EmployeePK empPk = new EmployeePK();
empPk.setDeptId(1);
empPk.setEmpId(23);
Employee emp = new Employee();
emp.setEmpPK(empPk);
emp.setFirstName("Lakshmana Rao");
emp.setLastName("Gurram");
try (Session session = sessionFactory.openSession()) {
session.beginTransaction();
session.persist(emp);
session.flush();
session.getTransaction().commit();
List<Employee> emps = loadAllData(Employee.class, session);
for (Employee emp1 : emps) {
System.out.println(emp1);
}
}
}
}
Total project structure looks like below.
Run App.java, you will see below messages in the console.
Aug 23, 2022 4:53:35 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 6.1.2.Final
Aug 23, 2022 4:53:35 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using built-in connection pool (not intended for production use)
Aug 23, 2022 4:53:35 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: Loaded JDBC driver class: org.postgresql.Driver
Aug 23, 2022 4:53:35 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001012: Connecting with JDBC URL [jdbc:postgresql://127.0.0.1:5432/test]
Aug 23, 2022 4:53:35 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=postgres}
Aug 23, 2022 4:53:35 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Aug 23, 2022 4:53:35 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH10001115: Connection pool size: 20 (min=1)
Aug 23, 2022 4:53:35 PM org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl logSelectedDialect
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
Aug 23, 2022 4:53:35 PM org.hibernate.mapping.RootClass checkCompositeIdentifier
WARN: HHH000038: Composite-id class does not override equals(): com.sample.app.entity.EmployeePK
Aug 23, 2022 4:53:35 PM org.hibernate.mapping.RootClass checkCompositeIdentifier
WARN: HHH000039: Composite-id class does not override hashCode(): com.sample.app.entity.EmployeePK
Hibernate:
drop table if exists employees cascade
Aug 23, 2022 4:53:36 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@32b0876c] 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.
Aug 23, 2022 4:53:36 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Aug 23, 2022 4:53:36 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: table "employees" does not exist, skipping
Hibernate:
create table employees (
deptId integer not null,
empId integer not null,
firstName varchar(255),
lastName varchar(255),
primary key (deptId, empId)
)
Aug 23, 2022 4:53:36 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@606f81b5] 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.
Aug 23, 2022 4:53:36 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
employees
(firstName, lastName, deptId, empId)
values
(?, ?, ?, ?)
Hibernate:
select
e1_0.deptId,
e1_0.empId,
e1_0.firstName,
e1_0.lastName
from
employees e1_0
Employee [empPK=EmployeePK [empId=23, deptId=1], firstName=Lakshmana Rao, lastName=Gurram]
Query PostgreSQL to confirm the generated DDL.
test=# \d+ employees;
Table "public.employees"
Column | Type | Collation | Nullable | Default | Storage | Compression | Stats target | Description
-----------+------------------------+-----------+----------+---------+----------+-------------+--------------+-------------
deptid | integer | | not null | | plain | | |
empid | integer | | not null | | plain | | |
firstname | character varying(255) | | | | extended | | |
lastname | character varying(255) | | | | extended | | |
Indexes:
"employees_pkey" PRIMARY KEY, btree (deptid, empid)
Access method: heap
test=#
You can download this application from this link.
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