persistence xml file equivalent java configuration with spring boot

Question

I am working on a spring boot project in which I have entities with @Entity Decorator which do not have @Id decorator because they are views and not tables. this is why I have a persistence.xml file which says that the classes processed hibernate here

Classe A

package com.lma.flad;
    @Entity
      class ClassA{
          private String name;
          private String surName
       }

classe B

package com.lma.flad;
    @Entity
      class ClassB{
          @Id
          private Long id
          private String name;
          private String surName
       }

classe C

package com.lma.flad;
    @Entity
      class ClassC{
          @ID
          private Long id
          private String name;
          private String surName
       }

persistance.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
             xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema- 
             instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
             http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
    <persistence-unit name="dtmowliance">

        <class>com.lma.flad.ClassB</class>
        <class>com.lma.flad.ClassC</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>
        <shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode>
        <properties>
            <property name="hibernate.cache.region.factory_class"
                      value="org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/>
        </properties>
    </persistence-unit>
</persistence>

in this case, hibernate will only analyze the classes found in the persistence xml file (classA and Class B)
How i can do the persistence.xml with java config in spring boot

Answer 1

Since you have created the Entity classes (JPA), you have to follow the subsequest steps:

1. Create JPA Repository

Imports: Common for 3 Entities

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

Repository for each Entity

@Repository
public interface ClassARepository extends JpaRepository<ClassA, Long> {

}
@Repository
public interface ClassBRepository extends JpaRepository<ClassB, Long> {

}
@Repository
public interface ClassCRepository extends JpaRepository<ClassC, Long> {

}

2. Properties Configuration: Configurating application.properties file to connect database to JPA code.

    spring.datasource.url=jdbc:h2:file:~/test
    spring.datasource.driverClassName=org.h2.Driver
    spring.datasource.username=sa
    spring.datasource.password=
    spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

    # Enabling H2 Console
    spring.h2.console.enabled=true

    # Custom H2 Console URL
    spring.h2.console.path=/h2-console

    #Turn Statistics on and log SQL stmts

    spring.jpa.show-sql=true
    spring.jpa.properties.hibernate.format_sql=true
    spring.jpa.hibernate.ddl-auto=create-drop

    #If want to see very extensive logging
    spring.jpa.properties.hibernate.generate_statistics=true
    logging.level.org.hibernate.type=trace
    logging.level.org.hibernate.stat=debug

3.Spring Boot to test your connectivity with database and JPA

import java.util.Optional;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import <your-path>.entity.ClassA;//change accordingly
import <your-path>.entity.ClassB;//change accordingly
import <your-path>.entity.ClassA;//change accordingly
import <your-path>.repository.ClassARepository;// change accordingly
import <your-path>.repository.ClassBRepository;// change accordingly
import <your-path>.repository.ClassCRepository;// change accordingly

@SpringBootApplication
public class DB2JPAApplication implements CommandLineRunner {

    private Logger logger = LoggerFactory.getLogger(this.getClass());

    @Autowired
    ClassARepository classArepository;

    @Autowired
    ClassBRepository classBrepository;

    @Autowired
    ClassCRepository classCrepository;

    public static void main(String[] args) {
        SpringApplication.run(DB2JPAApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception 
    {       
        Optional<ClassAEntity> classC = repository.findById(2L);

        logger.info("ClassC id 2 -> {}", classC.get());

        Optional<ClassAEntity> classB = repository.findById(2L);

        logger.info("ClassB id 2 -> {}", classB.get());
    }

NOTE:

• Your classA has no @Id. JPA makes it mandatory to have an ID coloumn.

• Change Entity and Reppsitory imports in DB2JPAApplication class