Persistence Policy Models using JPA/JDBC/Eclipselink/MariaDB

Java Persistence API

The Java Persistence API (JPA) is a specification of Java and it is a standard technology. It is used to persist data between Java object and relational database. JPA acts as a bridge between object-oriented domain models and relational database systems. As JPA is just a specification, it doesn't perform any operation by itself. By itself, JPA is not a tool or framework; rather, it defines a set of concepts that can be implemented by any tool or framework. While JPA's object-relational mapping (ORM) model was originally based on Hibernate, it has since evolved.

JPA vs Hibernate

JPA is a standard, while Hibernate is not. In hibernate, we use Session for handling the persistence of data, while in JPA, we use Entity Manager. The query language in Hibernate is Hibernate Query language, while in JPA, the query language is Java Persistence query language. Hibernate is one of the most JPA providers.

Spring Data JPA

Spring Data JPA, part of the larger Spring Data family, makes it easy to easily implement JPA based repositories. This module deals with enhanced support for JPA based data access layers. It makes it easier to build Spring-powered applications that use data access technologies.
It provides the following key dependencies:

Hibernate: One of the most popular JPA implementations.
Spring Data JPA: Helps you to implement JPA-based repositories.
Spring ORM: Core ORM support from the Spring Framework.

Source: https://spring.io/projects/spring-data-jpa

Spring and EclipseLink

By default Spring uses Hibernate as the default JPA vendor. Although Hibernate is a good choice, someone may prefers to use EclipseLink as it was supposed to be the reference implementation for the Java Persistence JSR.
How configuring Spring-Boot to use EclipseLink as the JPA provider: https://blog.marcnuri.com/spring-data-jpa-eclipselink-configuring-spring-boot-to-use-eclipselink-as-the-jpa-provider/

Jakarta Persistence

Jakarta Persistence defines a standard for management of persistence and object/relational mapping in Java(R) environments.

Connection Pools

A connection pool is a cache of database connections maintained so that the connections can be reused when future requests to the database are required. Connection pools are used to enhance the performance of executing commands on a database. Opening and maintaining a database connection for each user, especially requests made to a dynamic database-driven website application, is costly and wastes resources. In connection pooling, after a connection is created, it is placed in the pool and it is used again so that a new connection does not have to be established. If all the connections are being used, a new connection is made and is added to the pool. Connection pooling also cuts down on the amount of time a user must wait to establish a connection to the database.

HikariCP

HikariCP is a very lightweight (at roughly 130Kb) and lightning-fast JDBC connection pooling framework developed by Brett Wooldridge around 2012. It is a default in SpringBoot.

HikariCP-benchmark: https://github.com/brettwooldridge/HikariCP-benchmark

Transaction management

Transaction management refers to the tasks of processing multiple transactions issued by various clients of a database server in such a way that the ACID contract can be fulfilled, that is, the properties of atomicity, consistency preservation, isolation, and durability of each individual transaction can be guaranteed. Transaction management is generally understood as requiring serializability-based concurrency control as well as recovery from failures. Concurrency control is the task of scheduling transactions such that their serializability can be guaranteed, while recovery has to restore a consistent database state after a system or media failure. Assuming that the database server is in charge of the “C,” the former guarantees the “I” in ACID, the latter the “A” and “D” properties. Transaction management has to be highly efficient, as modern transaction servers need to accommodate thousands of transactions...

The Spring Framework provides a consistent abstraction for transaction management. The Spring Framework’s declarative transaction management is made possible with Spring aspect-oriented programming (AOP), although, as the transactional aspects code comes with the Spring Framework distribution and may be used in a boilerplate fashion, AOP concepts do not generally have to be understood to make effective use of this code.

Source: https://docs.spring.io/spring-framework/docs/5.3.7/reference/html/data-access.html#transaction

Aspect-Oriented Programming

Aspect-Oriented Programming (AOP) complements Object-Oriented Programming (OOP) by providing another way of thinking about program structure. The key unit of modularity in OOP is the class, whereas in AOP the unit of modularity is the aspect. Aspects enable the modularization of concerns such as transaction management that cut across multiple types and objects. (Such concerns are often termed crosscutting concerns in AOP literature.)
One of the key components of Spring is the AOP framework. While the Spring IoC (Inversion of control) container does not depend on AOP, meaning you do not need to use AOP if you don’t want to, AOP complements Spring IoC to provide a very capable middleware solution.

Source: https://docs.spring.io/spring-framework/docs/5.3.7/reference/html/core.html#aop

Use a Higher-level Database Migration Tool

Spring Boot supports two higher-level migration tools: Flyway and Liquibase.

Example how how to set things up with Liquibase: https://github.com/spring-projects/spring-boot/tree/v2.1.18.RELEASE/spring-boot-samples/spring-boot-sample-liquibase

Policy Framework - Models

Models are implemented using Jakarta Persistence. Spring Data JPA needs same implementation.

JpaToscaProperty

import javax.persistence.Column;
import javax.persistence.ElementCollection;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.Table;


@Entity
@Table(name = "ToscaProperty")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@Data
@EqualsAndHashCode(callSuper = false)
public class JpaToscaProperty extends PfConcept implements PfAuthorative<ToscaProperty> {
    private static final long serialVersionUID = 1675770231921107988L;

    @EmbeddedId
    @VerifyKey
    @NotNull
    private PfReferenceKey key;

    @Column
    @VerifyKey
    @NotNull
    private PfConceptKey type;

    @Column
    @NotBlank
    private String description;

Spring Repository

With Spring Data JPA, is a good choice to implement repositories.
The goal of Spring Data repository abstraction is to significantly reduce the amount of boilerplate code required to implement data access layers for various persistence stores.

Source: https://docs.spring.io/spring-data/data-commons/docs/2.5.1/reference/html/#repositories

JpaToscaPropertyRepository

@Repository
public interface JpaToscaPropertyRepository extends JpaRepository<JpaToscaProperty, PfReferenceKey> {

}

and also it needs to implement a JUnit test

JpaToscaPropertyRepositoryTest

@ExtendWith(SpringExtension.class)
@DataJpaTest
@Import(value = ParticipantPolicyParameters.class)
@TestPropertySource(locations = {"classpath:application_test.properties"})
class JpaToscaPropertyRepositoryTest {

    @Autowired
    private JpaToscaPropertyRepository toscaPropertyRepository;

    @Test
    void test() {
        JpaToscaProperty toscaProperty = new JpaToscaProperty();
        PfReferenceKey key = toscaProperty.getKey();

        Map<String, String> metadata = new HashMap<>();
        metadata.put("Key", "Value");
        metadata.put("K", "V");

        List<JpaToscaConstraint> constraints = new ArrayList<>();
        String[] list = new String[] {"First", "Second"};
        constraints.add(new JpaToscaConstraintValidValues(Stream.of(list).collect(Collectors.toList())));

        toscaProperty.setDefaultValue("DefaultValue");
        toscaProperty.setDescription("Description");
        toscaProperty.setRequired(true);
        toscaProperty.setStatus(ToscaProperty.Status.EXPERIMENTAL);
        toscaProperty.setMetadata(metadata);
        toscaProperty.setConstraints(constraints);
        toscaPropertyRepository.save(toscaProperty);

        Optional<JpaToscaProperty> opt = toscaPropertyRepository.findById(key);
        assertThat(opt).isNotEmpty();
        JpaToscaProperty actual = opt.get();
        assertThat(actual.getDefaultValue()).isEqualTo(toscaProperty.getDefaultValue());
        assertThat(actual.getDescription()).isEqualTo(toscaProperty.getDescription());
        assertThat(actual.isRequired()).isEqualTo(toscaProperty.isRequired());
        assertThat(actual.getStatus()).isEqualTo(toscaProperty.getStatus());
        assertThat(actual.getType()).isEqualTo(toscaProperty.getType());
        assertThat(actual.getConstraints()).isEqualTo(toscaProperty.getConstraints());
    }
}

Using Dao

Dao objects are already implemented in Policy Framework, and there is a way to use them and avoid to create repositories, but It needs to create a new DefaultPfDao class that uses the Entity Manger with no "begin transaction" and no "commit".

DefaultPfDao

EntityManager is not thread safe, and it need to use @PersistenceContext annotation, so Spring will inject a thread-safe proxy for the actual transactional EntityManager.

PolicyModelsProviderImpl

Spring Service

Example how to convert ControlLoopInstantiationProvider class in Spring style using "@Service" and "@Transactional"

ControlLoopInstantiationProvider

Transaction

Transaction Propagation in SpringBoot:

REQUIRED is the default propagation. Spring checks if there is an active transaction, then it creates a new one if nothing existed;
For SUPPORTS, Spring first checks if an active transaction exists. If a transaction exists, then the existing transaction will be used. If there isn't a transaction, it is executed non-transactional;
When the propagation is MANDATORY, if there is an active transaction, then it will be used. If there isn't an active transaction, then Spring throws an exception;
For transactional logic with NEVER propagation, Spring throws an exception if there's an active transaction;
NOT_SUPPORTED, Spring at first suspends the current transaction if it exists, then the business logic is executed without a transaction;
When the propagation is REQUIRES_NEW, Spring suspends the current transaction if it exists and then creates a new one.

Read only Transaction

If the transaction is effectively read-only, it allows for corresponding optimizations at runtime. (https://stackoverflow.com/questions/1614139/spring-transactional-read-only-propagation)

Note: In Spring, @Transactional works by creating a proxy of the class and intercepting the annotated method (AOP Proxies). This means that @Transactional doesn't work if you are calling the annotated method from another method of the same class.

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