Different Strategies for ID generation in JPA

[pwgit-create]

Below is a simple example of how to create a test that demonstrates different strategies for ID
generation in JPA (using Spring Data JPA). This will include IDENTITY, SEQUENCE, TABLE, and ASSIGNED
strategies.

First, make sure you have the necessary dependencies in your pom.xml or build.gradle:

For Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <scope>runtime</scope>
</dependency>

For Gradle:

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    runtimeOnly 'com.h2database:h2'
}

Next, create the entity classes with different ID generation strategies:

Entity Classes

IdentityEntity.java

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class IdentityEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    // Getters and Setters
}

SequenceEntity.java

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;

@Entity
public class SequenceEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq-gen")
    @SequenceGenerator(name = "seq-gen", sequenceName = "my_sequence")
    private Long id;
    private String name;

    // Getters and Setters
}

TableEntity.java

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.TableGenerator;

@Entity
public class TableEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "table-gen")
    @TableGenerator(name = "table-gen", table = "id_table")
    private Long id;
    private String name;

    // Getters and Setters
}

AssignedEntity.java

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class AssignedEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.ASSIGNED)
    private Long id;
    private String name;

    // Getters and Setters
}

Repository Interfaces

IdentityEntityRepository.java

import org.springframework.data.jpa.repository.JpaRepository;

public interface IdentityEntityRepository extends JpaRepository<IdentityEntity, Long> {
}

Repeat similarly for SequenceEntity, TableEntity, and AssignedEntity.

Test Class

JpaIdGenerationTest.java

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;

@DataJpaTest
public class JpaIdGenerationTest {

    @Autowired
    private IdentityEntityRepository identityEntityRepository;

    @Autowired
    private SequenceEntityRepository sequenceEntityRepository;

    @Autowired
    private TableEntityRepository tableEntityRepository;

    @Autowired
    private AssignedEntityRepository assignedEntityRepository;

    @Test
    public void testIdentityStrategy() {
        IdentityEntity entity = new IdentityEntity();
        entity.setName("Identity Test");
        identityEntityRepository.save(entity);
        System.out.println("Generated ID (IDENTITY): " + entity.getId());
    }

    @Test
    public void testSequenceStrategy() {
        SequenceEntity entity = new SequenceEntity();
        entity.setName("Sequence Test");
        sequenceEntityRepository.save(entity);
        System.out.println("Generated ID (SEQUENCE): " + entity.getId());
    }

    @Test
    public void testTableStrategy() {
        TableEntity entity = new TableEntity();
        entity.setName("Table Test");
        tableEntityRepository.save(entity);
        System.out.println("Generated ID (TABLE): " + entity.getId());
    }

    @Test
    public void testAssignedStrategy() {
        AssignedEntity entity = new AssignedEntity();
        entity.setId(100L); // Manually assigned ID
        entity.setName("Assigned Test");
        assignedEntityRepository.save(entity);
        System.out.println("Assigned ID (ASSIGNED): " + entity.getId());
    }
}

Explanation

• IdentityEntity: Uses GenerationType.IDENTITY which relies on the database's auto-increment feature.
• SequenceEntity: Uses GenerationType.SEQUENCE with a sequence generator, requiring you to define a sequence
  in your database schema.
• TableEntity: Uses GenerationType.TABLE with a table generator. This will create an additional table for ID
  management if not already present.
• AssignedEntity: Uses GenerationType.ASSIGNED, meaning you must assign the IDs manually before persisting
  entities.

Run these tests to observe how each strategy handles ID generation and confirm that they work as expected in your
environment.