Giới thiệu Spring Data JPA và JpaRepository

01-jparepository/
  docker-compose.yml           MySQL 8.4, database shop, user app (cổng 3307)
  pom.xml                       parent Boot 4.1.1, starter data-jpa, mysql-connector-j, test, testcontainers
  src/main/java/dev/canhdominich/boot/jpa/
    JpaApplication.java         @SpringBootApplication
    Level.java                  enum BASIC, ADVANCED
    Student.java                entity: id tự tăng, tên, email duy nhất, level
    StudentRepository.java      interface JpaRepository có hai truy vấn dẫn xuất
    SqlRecorder.java            StatementInspector ghi lại mọi câu SQL
    RepositoryDemo.java         chạy các thí nghiệm và in SQL

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>4.1.1</version>
        <relativePath/>
    </parent>

    <groupId>dev.canhdominich.javabackend</groupId>
    <artifactId>jpa-repository</artifactId>
    <version>1.0.0</version>
    <name>Spring Data JPA - JpaRepository</name>

    <properties>
        <java.version>17</java.version>
        <main.class>dev.canhdominich.boot.jpa.RepositoryDemo</main.class>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.testcontainers</groupId>
            <artifactId>testcontainers-mysql</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <configuration>
                    <executable>java</executable>
                    <arguments>
                        <argument>-classpath</argument>
                        <classpath/>
                        <argument>${main.class}</argument>
                    </arguments>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

services:
  mysql:
    image: mysql:8.4
    container_name: jdbc-lab-mysql
    environment:
      MYSQL_ROOT_PASSWORD: root_pw
      MYSQL_DATABASE: shop
      MYSQL_USER: app
      MYSQL_PASSWORD: app_pw
    ports:
      - "${MYSQL_PORT:-3307}:3306"
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "-uroot", "-proot_pw"]
      interval: 3s
      timeout: 3s
      retries: 30

docker compose up -d
docker compose ps

package dev.canhdominich.boot.jpa;

import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.EnumType;
import jakarta.persistence.Enumerated;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Student {

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

    private String name;

    @Column(unique = true)
    private String email;

    @Enumerated(EnumType.STRING)
    private Level level;

    protected Student() {
    }

    public Student(String name, String email, Level level) {
        this.name = name;
        this.email = email;
        this.level = level;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public Level getLevel() {
        return level;
    }
}

package dev.canhdominich.boot.jpa;

public enum Level {
    BASIC,
    ADVANCED
}

package dev.canhdominich.boot.jpa;

import java.util.List;
import java.util.Optional;
import org.springframework.data.jpa.repository.JpaRepository;

public interface StudentRepository extends JpaRepository<Student, Long> {

    Optional<Student> findByEmail(String email);

    List<Student> findByLevel(Level level);
}

package dev.canhdominich.boot.jpa;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class JpaApplication {

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

package dev.canhdominich.boot.jpa;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.hibernate.resource.jdbc.spi.StatementInspector;

public class SqlRecorder implements StatementInspector {

    private static final List<String> STATEMENTS = Collections.synchronizedList(new ArrayList<>());

    @Override
    public String inspect(String sql) {
        STATEMENTS.add(sql.replaceAll("\\s+", " ").trim());
        return sql;
    }

    public static void clear() {
        STATEMENTS.clear();
    }

    public static List<String> statements() {
        synchronized (STATEMENTS) {
            return new ArrayList<>(STATEMENTS);
        }
    }
}

package dev.canhdominich.boot.jpa;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.springframework.aop.framework.AopProxyUtils;
import org.springframework.boot.SpringApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.transaction.support.TransactionTemplate;

public class RepositoryDemo {

    public static void main(String[] args) {
        run(env("JDBC_URL", "jdbc:mysql://localhost:3307/shop"), env("DB_USER", "app"), env("DB_PASSWORD", "app_pw")).forEach(System.out::println);
    }

    public static List<String> run(String url, String user, String password) {
        Map<String, Object> properties = new HashMap<>();
        properties.put("spring.datasource.url", url);
        properties.put("spring.datasource.username", user);
        properties.put("spring.datasource.password", password);
        properties.put("spring.jpa.hibernate.ddl-auto", "create-drop");
        properties.put("spring.jpa.properties.hibernate.session_factory.statement_inspector", SqlRecorder.class.getName());
        properties.put("spring.main.web-application-type", "none");
        properties.put("spring.main.banner-mode", "off");
        properties.put("logging.level.root", "OFF");
        SpringApplication application = new SpringApplication(JpaApplication.class);
        application.setDefaultProperties(properties);
        List<String> lines = new ArrayList<>();
        try (ConfigurableApplicationContext context = application.run()) {
            StudentRepository repository = context.getBean(StudentRepository.class);
            TransactionTemplate transaction = context.getBean(TransactionTemplate.class);
            lines.add("repository object: " + repository.getClass().getSimpleName().replaceAll("[0-9]+$", "") + " (proxy), target " + AopProxyUtils.ultimateTargetClass(repository).getSimpleName());
            lines.add("-- save");
            SqlRecorder.clear();
            Student an = repository.save(new Student("An", "an@example.com", Level.BASIC));
            report(lines, "save(new Student) gives id " + (an.getId() != null));
            Student found = repository.findById(an.getId()).orElseThrow();
            found.setName("An Nguyen");
            SqlRecorder.clear();
            repository.save(found);
            report(lines, "save(detached student with an id)");
            SqlRecorder.clear();
            transaction.executeWithoutResult(status -> repository.findById(an.getId()).orElseThrow().setName("An N."));
            report(lines, "change inside one transaction, no save call");
            lines.add("-- reading");
            SqlRecorder.clear();
            repository.findById(an.getId());
            report(lines, "findById");
            SqlRecorder.clear();
            repository.existsById(an.getId());
            report(lines, "existsById");
            SqlRecorder.clear();
            repository.count();
            report(lines, "count");
            SqlRecorder.clear();
            transaction.executeWithoutResult(status -> repository.getReferenceById(an.getId()));
            report(lines, "getReferenceById, id only used");
            SqlRecorder.clear();
            transaction.executeWithoutResult(status -> repository.getReferenceById(an.getId()).getName());
            report(lines, "getReferenceById, then getName");
            lines.add("-- derived queries");
            SqlRecorder.clear();
            repository.findByEmail("an@example.com");
            report(lines, "findByEmail");
            SqlRecorder.clear();
            repository.findByLevel(Level.BASIC);
            report(lines, "findByLevel");
            lines.add("-- saving and deleting several");
            SqlRecorder.clear();
            repository.saveAll(List.of(new Student("B1", "b1@example.com", Level.BASIC), new Student("B2", "b2@example.com", Level.BASIC), new Student("B3", "b3@example.com", Level.ADVANCED)));
            report(lines, "saveAll of 3");
            SqlRecorder.clear();
            repository.deleteById(an.getId());
            report(lines, "deleteById");
            SqlRecorder.clear();
            repository.deleteAllInBatch();
            report(lines, "deleteAllInBatch");
            lines.add("-- a duplicate email");
            repository.save(new Student("C", "c@example.com", Level.BASIC));
            try {
                repository.save(new Student("C again", "c@example.com", Level.BASIC));
            } catch (RuntimeException e) {
                List<String> chain = new ArrayList<>();
                for (Throwable t = e; t != null; t = t.getCause()) {
                    chain.add(t.getClass().getSimpleName());
                }
                lines.add("exception chain: " + chain);
            }
        }
        return lines;
    }

    private static void report(List<String> lines, String label) {
        List<String> statements = SqlRecorder.statements();
        lines.add(label + " -> " + statements.size() + " statements");
        statements.forEach(sql -> lines.add("    " + sql));
        SqlRecorder.clear();
    }

    private static String env(String name, String fallback) {
        String value = System.getenv(name);
        return value == null || value.isBlank() ? fallback : value;
    }
}

repository object: $Proxy (proxy), target SimpleJpaRepository
-- save
save(new Student) gives id true -> 1 statements
    insert into student (email,level,name) values (?,?,?)
save(detached student with an id) -> 2 statements
    select s1_0.id,s1_0.email,s1_0.level,s1_0.name from student s1_0 where s1_0.id=?
    update student set email=?,level=?,name=? where id=?
change inside one transaction, no save call -> 2 statements
    select s1_0.id,s1_0.email,s1_0.level,s1_0.name from student s1_0 where s1_0.id=?
    update student set email=?,level=?,name=? where id=?
-- reading
findById -> 1 statements
    select s1_0.id,s1_0.email,s1_0.level,s1_0.name from student s1_0 where s1_0.id=?
existsById -> 1 statements
    select count(*) from student s1_0 where s1_0.id=?
count -> 1 statements
    select count(*) from student s1_0
getReferenceById, id only used -> 0 statements
getReferenceById, then getName -> 1 statements
    select s1_0.id,s1_0.email,s1_0.level,s1_0.name from student s1_0 where s1_0.id=?
-- derived queries
findByEmail -> 1 statements
    select s1_0.id,s1_0.email,s1_0.level,s1_0.name from student s1_0 where s1_0.email=?
findByLevel -> 1 statements
    select s1_0.id,s1_0.email,s1_0.level,s1_0.name from student s1_0 where s1_0.level=?
-- saving and deleting several
saveAll of 3 -> 3 statements
    insert into student (email,level,name) values (?,?,?)
    insert into student (email,level,name) values (?,?,?)
    insert into student (email,level,name) values (?,?,?)
deleteById -> 2 statements
    select s1_0.id,s1_0.email,s1_0.level,s1_0.name from student s1_0 where s1_0.id=?
    delete from student where id=?
deleteAllInBatch -> 1 statements
    delete s1_0 from student s1_0
-- a duplicate email
exception chain: [DataIntegrityViolationException, ConstraintViolationException, SQLIntegrityConstraintViolationException]