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AnghelLeonardAnghelLeonard
committedNov 17, 2021
Intercept the generated SQL for logging or altering
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‎HibernateSpringBootInterceptSql/README.md

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**[How To Avoid `LazyInitializationException` Via `JOIN FETCH`](https://github.com/AnghelLeonard/Hibernate-SpringBoot/tree/master/HibernateSpringBootJoinFetch)**
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**See also:**
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- [LEFT JOIN FETCH](https://github.com/AnghelLeonard/Hibernate-SpringBoot/tree/master/HibernateSpringBootLeftJoinFetch)
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- [JOIN VS. JOIN FETCH](https://github.com/AnghelLeonard/Hibernate-SpringBoot/tree/master/HibernateSpringBootJoinVSJoinFetch)
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**Description:** Typically, when we get a `LazyInitializationException` we tend to modify the association fetching type from `LAZY` to `EAGER`. That is very bad! This is a [code smell](https://vladmihalcea.com/eager-fetching-is-a-code-smell/). Best way to avoid this exception is to rely on `JOIN FETCH` (if you plan to modify the fetched entities) or `JOIN` + DTO (if the fetched data is only read). `JOIN FETCH` allows associations to be initialized along with their parent objects using a single `SELECT`. This is particularly useful for fetching associated collections.
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This application is a `JOIN FETCH` example for avoiding `LazyInitializationException`.
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**Key points:**
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- define two related entities (e.g., `Author` and `Book` in a `@OneToMany` lazy-bidirectional association)
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- write a JPQL `JOIN FETCH` to fetch an author including his books
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- write a JPQL `JOIN FETCH` (or `JOIN`) to fetch a book including its author
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**Output example:**\
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![](https://github.com/AnghelLeonard/Hibernate-SpringBoot/blob/master/HibernateSpringBootJoinFetch/hibernate%20spring%20boot%20join%20fetch.png)
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-----------------------------------------------------------------------------------------------------------------------
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<table>
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<tr><td><b>If you need a deep dive into the performance recipes exposed in this repository then I am sure that you will love my book "Spring Boot Persistence Best Practices"</b></td><td><b>If you need a hand of tips and illustrations of 100+ Java persistence performance issues then "Java Persistence Performance Illustrated Guide" is for you.</b></td></tr>
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<tr><td>
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<a href="https://www.apress.com/us/book/9781484256251"><p align="left"><img src="https://github.com/AnghelLeonard/Hibernate-SpringBoot/blob/master/Spring%20Boot%20Persistence%20Best%20Practices.jpg" height="500" width="450"/></p></a>
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</td><td>
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<a href="https://leanpub.com/java-persistence-performance-illustrated-guide"><p align="right"><img src="https://github.com/AnghelLeonard/Hibernate-SpringBoot/blob/master/Java%20Persistence%20Performance%20Illustrated%20Guide.jpg" height="500" width="450"/></p></a>
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</td></tr></table>
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-----------------------------------------------------------------------------------------------------------------------
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‎HibernateSpringBootInterceptSql/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.jpa</groupId>
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<artifactId>HibernateSpringBootInterceptSql</artifactId>
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<version>1.0</version>
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<packaging>jar</packaging>
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<name>HibernateSpringBootInterceptSql</name>
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<description>JPA project for Spring Boot</description>
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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>2.1.4.RELEASE</version>
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<relativePath/> <!-- lookup parent from repository -->
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</parent>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
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<java.version>1.8</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-data-jpa</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-jdbc</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-web</artifactId>
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</dependency>
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<dependency>
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<groupId>mysql</groupId>
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<artifactId>mysql-connector-java</artifactId>
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<scope>runtime</scope>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-test</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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</plugin>
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</plugins>
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</build>
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</project>

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

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package com.bookstore;
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import com.bookstore.entity.Author;
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import com.bookstore.entity.Book;
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import com.bookstore.service.BookstoreService;
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import org.springframework.boot.ApplicationRunner;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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import org.springframework.context.annotation.Bean;
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@SpringBootApplication
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public class MainApplication {
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private final BookstoreService bookstoreService;
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public MainApplication(BookstoreService bookstoreService) {
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this.bookstoreService = bookstoreService;
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}
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public static void main(String[] args) {
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SpringApplication.run(MainApplication.class, args);
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}
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@Bean
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public ApplicationRunner init() {
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return args -> {
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Author author = bookstoreService.fetchAuthorWithBooksByName();
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System.out.println("\nAuthor name: " + author.getName() + " Books: " + author.getBooks() + "\n");
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Book book = bookstoreService.fetchBookWithAuthorByIsbn();
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System.out.println("\nTitle: " + book.getTitle() + " author: " + book.getAuthor() + "\n");
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};
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}
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}

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

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package com.bookstore.entity;
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import java.io.Serializable;
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import java.util.ArrayList;
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import java.util.List;
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import javax.persistence.CascadeType;
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import javax.persistence.Entity;
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import javax.persistence.Id;
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import javax.persistence.OneToMany;
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@Entity
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public class Author implements Serializable {
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private static final long serialVersionUID = 1L;
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@Id
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private Long id;
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private String name;
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private String genre;
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private int age;
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@OneToMany(cascade = CascadeType.ALL,
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mappedBy = "author", orphanRemoval = true)
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private List<Book> books = new ArrayList<>();
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public void addBook(Book book) {
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this.books.add(book);
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book.setAuthor(this);
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}
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public void removeBook(Book book) {
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book.setAuthor(null);
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this.books.remove(book);
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}
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public Long getId() {
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return id;
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}
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public void setId(Long id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public String getGenre() {
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return genre;
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}
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public void setGenre(String genre) {
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this.genre = genre;
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}
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public int getAge() {
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return age;
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}
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public void setAge(int age) {
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this.age = age;
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}
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public List<Book> getBooks() {
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return books;
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}
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public void setBooks(List<Book> books) {
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this.books = books;
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}
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@Override
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public String toString() {
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return "Author{" + "id=" + id + ", name=" + name
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+ ", genre=" + genre + ", age=" + age + '}';
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}
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}

‎HibernateSpringBootInterceptSql/src/main/java/com/bookstore/entity/Book.java

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package com.bookstore.entity;
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import java.io.Serializable;
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import javax.persistence.Entity;
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import javax.persistence.FetchType;
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import javax.persistence.Id;
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import javax.persistence.JoinColumn;
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import javax.persistence.ManyToOne;
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@Entity
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public class Book implements Serializable {
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private static final long serialVersionUID = 1L;
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@Id
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private Long id;
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private String title;
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private String isbn;
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@ManyToOne(fetch = FetchType.LAZY)
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@JoinColumn(name = "author_id")
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private Author author;
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public Long getId() {
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return id;
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}
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public void setId(Long id) {
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this.id = id;
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}
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public String getTitle() {
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return title;
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}
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public void setTitle(String title) {
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this.title = title;
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}
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public String getIsbn() {
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return isbn;
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}
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public void setIsbn(String isbn) {
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this.isbn = isbn;
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}
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public Author getAuthor() {
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return author;
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}
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public void setAuthor(Author author) {
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this.author = author;
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}
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@Override
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public boolean equals(Object obj) {
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if (this == obj) {
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return true;
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}
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if (!(obj instanceof Book)) {
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return false;
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}
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return id != null && id.equals(((Book) obj).id);
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}
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@Override
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public int hashCode() {
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return 2021;
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}
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@Override
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public String toString() {
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return "Book{" + "id=" + id + ", title=" + title + ", isbn=" + isbn + '}';
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}
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}

‎HibernateSpringBootInterceptSql/src/main/java/com/bookstore/interceptor/SqlInspector.java

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package com.bookstore.interceptor;
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import org.hibernate.resource.jdbc.spi.StatementInspector;
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public class SqlInspector implements StatementInspector {
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@Override
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public String inspect(String sql) {
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System.out.println("The generated SQL is: " + sql);
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// you can modify the sql here or return null to return the same sql
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return null;
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}
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}

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

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package com.bookstore.repository;
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import com.bookstore.entity.Author;
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import org.springframework.data.jpa.repository.JpaRepository;
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import org.springframework.data.jpa.repository.Query;
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import org.springframework.stereotype.Repository;
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import org.springframework.transaction.annotation.Transactional;
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@Repository
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public interface AuthorRepository extends JpaRepository<Author, Long> {
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@Transactional(readOnly = true)
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@Query(value = "SELECT a FROM Author a JOIN FETCH a.books WHERE a.name = ?1")
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Author fetchAuthorWithBooksByName(String name);
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}

‎HibernateSpringBootInterceptSql/src/main/java/com/bookstore/repository/BookRepository.java

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package com.bookstore.repository;
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import com.bookstore.entity.Book;
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import org.springframework.data.jpa.repository.JpaRepository;
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import org.springframework.data.jpa.repository.Query;
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import org.springframework.stereotype.Repository;
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import org.springframework.transaction.annotation.Transactional;
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@Repository
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public interface BookRepository extends JpaRepository<Book, Long> {
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@Transactional(readOnly = true)
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@Query(value = "SELECT b FROM Book b JOIN FETCH b.author WHERE b.isbn = ?1")
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// or, via JOIN
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//@Query(value = "SELECT b, a FROM Book b JOIN b.author a WHERE b.isbn = ?1")
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Book fetchBookWithAuthorByIsbn(String isbn);
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}

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

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package com.bookstore.service;
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import com.bookstore.repository.AuthorRepository;
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import com.bookstore.repository.BookRepository;
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import com.bookstore.entity.Author;
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import com.bookstore.entity.Book;
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import org.springframework.stereotype.Service;
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@Service
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public class BookstoreService {
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private final AuthorRepository authorRepository;
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private final BookRepository bookRepository;
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public BookstoreService(AuthorRepository authorRepository,
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BookRepository bookRepository) {
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this.authorRepository = authorRepository;
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this.bookRepository = bookRepository;
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}
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public Author fetchAuthorWithBooksByName() {
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return authorRepository.fetchAuthorWithBooksByName("Joana Nimar");
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}
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public Book fetchBookWithAuthorByIsbn() {
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return bookRepository.fetchBookWithAuthorByIsbn("002-JN");
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}
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}

‎HibernateSpringBootInterceptSql/src/main/resources/application.properties

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spring.datasource.url=jdbc:mysql://localhost:3306/bookstoredb?createDatabaseIfNotExist=true
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spring.datasource.username=root
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spring.datasource.password=root
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spring.jpa.hibernate.ddl-auto=create
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spring.jpa.show-sql=true
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spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL8Dialect
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spring.jpa.open-in-view=false
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spring.datasource.initialization-mode=always
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spring.datasource.platform=mysql
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spring.jpa.properties.hibernate.session_factory.statement_inspector=com.bookstore.interceptor.SqlInspector

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