Best way to use @transactional

Author: AnghelLeonard

HibernateSpringBootTransactionalInRepository/README.md

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+**[Avoid Spring Redundant `save()` Call](https://github.com/AnghelLeonard/Hibernate-SpringBoot/tree/master/HibernateSpringBootRedundantSave)**
+ 
+**Description:** This application is an example when calling `save()` for an entity is redundant (not necessary).
+
+**Key points:**
+- at flush time, Hibernate relies on *dirty checking* mechanism to determine the potential modifications in entities 
+- for each modification, Hibernate automatically triggers the corresponding `UPDATE` statement without the need to explicitly call the `save()` method
+- behind the scene, this redundancy (calling `save()` when is not necessarily) doesn't affect the number of triggered queries, but it implies a performance penalty in the underlying Hibernate processes
+     
+<a href="https://leanpub.com/java-persistence-performance-illustrated-guide"><p align="center"><img src="https://github.com/AnghelLeonard/Hibernate-SpringBoot/blob/master/Java%20Persistence%20Performance%20Illustrated%20Guide.jpg" height="410" width="350"/></p></a>

HibernateSpringBootTransactionalInRepository/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.jpa</groupId>
+    <artifactId>HibernateSpringBootTransactionalInRepository</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+
+    <name>HibernateSpringBootTransactionalInRepository</name>
+    <description>JPA project for Spring Boot</description>
+
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.1.4.RELEASE</version>
+        <relativePath/> <!-- lookup parent from repository -->
+    </parent>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+        <java.version>1.8</java.version>                
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-data-jpa</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-jdbc</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.postgresql</groupId>
+            <artifactId>postgresql</artifactId>
+        </dependency>      
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+</project>

HibernateSpringBootTransactionalInRepository/src/main/java/com/bookstore/MainApplication.java

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+package com.bookstore;
+
+import com.bookstore.service.BookstoreService;
+import org.springframework.boot.ApplicationRunner;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+
+@SpringBootApplication
+public class MainApplication {
+
+    private final BookstoreService bookstoreService;
+
+    public MainApplication(BookstoreService bookstoreService) {
+        this.bookstoreService = bookstoreService;
+    }
+
+    public static void main(String[] args) {
+        SpringApplication.run(MainApplication.class, args);
+    }
+
+    @Bean
+    public ApplicationRunner init() {
+        return args -> {
+
+            bookstoreService.newAuthor();
+            System.out.println("=========================================");
+            System.out.println("=========================================");
+            System.out.println("=========================================");
+            bookstoreService.longRunningServiceMethod();
+            System.out.println("=========================================");
+        };
+    }
+}

HibernateSpringBootTransactionalInRepository/src/main/java/com/bookstore/entity/Author.java

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+package com.bookstore.entity;
+
+import java.io.Serializable;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class Author implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+
+    @Id
+    //@GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private int age;
+    private String name;
+    private String genre;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getGenre() {
+        return genre;
+    }
+
+    public void setGenre(String genre) {
+        this.genre = genre;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    @Override
+    public String toString() {
+        return "Author{" + "id=" + id + ", age=" + age
+                + ", name=" + name + ", genre=" + genre + '}';
+    }
+}

HibernateSpringBootTransactionalInRepository/src/main/java/com/bookstore/repository/AuthorRepository.java

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+package com.bookstore.repository;
+
+import com.bookstore.entity.Author;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Modifying;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.stereotype.Repository;
+import org.springframework.transaction.annotation.Transactional;
+
+@Repository
+@Transactional(readOnly = true)
+public interface AuthorRepository extends JpaRepository<Author, Long> {
+
+    @Query("SELECT a FROM Author a WHERE a.id = ?1")
+    public Author fetchById(long id);
+
+    @Transactional
+    @Modifying
+    @Query("DELETE FROM Author a WHERE a.name = ?1")
+    public int deleteByName(String name);
+}

HibernateSpringBootTransactionalInRepository/src/main/java/com/bookstore/service/BookstoreService.java

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+package com.bookstore.service;
+
+import com.bookstore.entity.Author;
+import com.bookstore.repository.AuthorRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+public class BookstoreService {
+
+    private final AuthorRepository authorRepository;
+
+    public BookstoreService(AuthorRepository authorRepository) {
+        this.authorRepository = authorRepository;
+    }
+
+    @Transactional
+    public void newAuthor() {
+        Author a1 = new Author();
+        a1.setName("Joana Nimar");
+        a1.setGenre("History");
+        a1.setId(4L);
+        a1.setAge(34);
+
+        authorRepository.save(a1);
+    }
+
+    @Transactional
+    public void longRunningServiceMethod() throws InterruptedException {
+
+        System.out.println("Service-method start ...");
+        System.out.println("Sleeping before triggering SQL to simulate a long running code ...");
+        Thread.sleep(40000);
+
+        Author author = authorRepository.fetchById(4L);
+        authorRepository.deleteByName(author.getName());
+
+        System.out.println("Service-method done ...");
+    }
+}

HibernateSpringBootTransactionalInRepository/src/main/resources/application.properties

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+spring.datasource.url=jdbc:postgresql://localhost:5432/postgres
+spring.datasource.username=postgres
+spring.datasource.password=root
+
+spring.jpa.hibernate.ddl-auto=create
+spring.jpa.show-sql=true
+
+spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQL95Dialect
+spring.jpa.properties.hibernate.format-sql=true
+
+spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true
+
+spring.jpa.open-in-view=false
+
+logging.level.ROOT=INFO
+logging.level.org.hibernate.engine.transaction.internal.TransactionImpl=DEBUG
+logging.level.org.springframework.orm.jpa=DEBUG
+logging.level.org.springframework.transaction=DEBUG
+
+logging.level.com.zaxxer.hikari.HikariConfig=DEBUG
+logging.level.com.zaxxer.hikari=TRACE
+
+spring.datasource.hikari.auto-commit=false
+spring.jpa.properties.hibernate.connection.provider_disables_autocommit=true