Spring Boot 4 Microservices & REST APIs · レッスン

CRUD操作の実行

Spring Data JPAの強力なリポジトリメソッドを使って、作成、読み取り、更新、削除の操作を実装します。

「CRUD操作の実行」はCoddyKit上の無料Spring Boot 4 Microservices & REST APIsレッスンです。これはレッスン6/6です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはSpring Boot 4 Microservices & REST APIs学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Spring Boot 4 Microservices & REST APIsコースには全6レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

CRUD Operations: The Core

Welcome to the heart of data management! Today, we'll master CRUD operations with Spring Data JPA. CRUD is a fundamental concept for almost any application that interacts with a database.

Create: Adding new data.
Read: Retrieving existing data.
Update: Modifying existing data.
Delete: Removing data.

Spring Data JPA provides powerful, easy-to-use methods for all of these!

Our Example Setup: Product

To demonstrate CRUD, we'll use a simple Product entity and its corresponding repository. You would have learned to set these up in previous lessons.

Here's our basic Product entity and ProductRepository interface:

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;

    public Product() {}
    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }

    // Getters and Setters (omitted for brevity)
    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 double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }

    @Override
    public String toString() {
        return "Product{id=" + id + ", name='" + name + "', price=" + price + "}";
    }
}

// ProductRepository.java
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
}

Creating New Data (C)

To create new data, we use the save() method from our repository. If the entity's ID is null (or 0 for primitive types), Spring Data JPA knows it's a new entry and will insert it into the database.

Try creating a new product:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Entity
class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name; this.price = price;
    }
    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 double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    @Override
    public String toString() { return "Product{id=" + id + ", name='" + name + "', price=" + price + "}"; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(Main.class, args);
        ProductRepository productRepository = context.getBean(ProductRepository.class);

        Product newProduct = new Product("Laptop", 1200.00);
        Product savedProduct = productRepository.save(newProduct);
        System.out.println("Created: " + savedProduct);
    }
}

Reading Data by ID (R)

To read a specific item, you often need its unique identifier (ID). The findById(ID id) method is perfect for this. It returns an Optional, which helps handle cases where the item might not exist.

Let's find the product we just created:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import java.util.Optional;

@Entity
class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name; this.price = price;
    }
    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 double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    @Override
    public String toString() { return "Product{id=" + id + ", name='" + name + "', price=" + price + "}"; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(Main.class, args);
        ProductRepository productRepository = context.getBean(ProductRepository.class);

        Product newProduct = new Product("Keyboard", 75.00);
        Product savedProduct = productRepository.save(newProduct);
        System.out.println("Created: " + savedProduct);

        Optional<Product> foundProduct = productRepository.findById(savedProduct.getId());
        foundProduct.ifPresent(p -> System.out.println("Found: " + p));
    }
}

Reading All Data (R)

What if you want to see all the products in your database? The findAll() method does exactly that! It returns a List of all entities of that type.

Let's retrieve all products:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import java.util.List;

@Entity
class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name; this.price = price;
    }
    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 double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    @Override
    public String toString() { return "Product{id=" + id + ", name='" + name + "', price=" + price + "}"; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(Main.class, args);
        ProductRepository productRepository = context.getBean(ProductRepository.class);

        productRepository.save(new Product("Mouse", 25.00));
        productRepository.save(new Product("Monitor", 300.00));

        List<Product> allProducts = productRepository.findAll();
        System.out.println("All Products:");
        allProducts.forEach(System.out::println);
    }
}

Updating Existing Data (U)

To update an existing item, you first retrieve it, modify its properties, and then call save() again. Spring Data JPA detects that the entity already has an ID, so it performs an update instead of an insert.

Let's update a product's price:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Entity
class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name; this.price = price;
    }
    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 double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    @Override
    public String toString() { return "Product{id=" + id + ", name='" + name + "', price=" + price + "}"; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(Main.class, args);
        ProductRepository productRepository = context.getBean(ProductRepository.class);

        Product existingProduct = new Product("Headphones", 150.00);
        productRepository.save(existingProduct);
        System.out.println("Original: " + existingProduct);

        existingProduct.setPrice(120.00); // Update the price
        Product updatedProduct = productRepository.save(existingProduct);
        System.out.println("Updated: " + updatedProduct);
    }
}

Deleting Data by ID (D)

To delete an item, you can use its ID with the deleteById(ID id) method. This is a common way to remove a specific record from the database.

Let's delete a product by its ID:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Entity
class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name; this.price = price;
    }
    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 double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    @Override
    public String toString() { return "Product{id=" + id + ", name='" + name + "', price=" + price + "}"; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(Main.class, args);
        ProductRepository productRepository = context.getBean(ProductRepository.class);

        Product productToDelete = new Product("Webcam", 50.00);
        productRepository.save(productToDelete);
        System.out.println("Product to delete: " + productToDelete);

        productRepository.deleteById(productToDelete.getId());
        System.out.println("Is product deleted? " + !productRepository.existsById(productToDelete.getId()));
    }
}

Deleting an Entity Object (D)

Alternatively, you can delete an entity by passing the actual entity object to the delete(T entity) method. This is useful if you've already retrieved the object and want to remove it.

Let's delete a product using its object:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Entity
class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    public Product() {}
    public Product(String name, double price) {
        this.name = name; this.price = price;
    }
    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 double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    @Override
    public String toString() { return "Product{id=" + id + ", name='" + name + "', price=" + price + "}"; }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {}

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(Main.class, args);
        ProductRepository productRepository = context.getBean(ProductRepository.class);

        Product productToRemove = new Product("Microphone", 80.00);
        productRepository.save(productToRemove);
        System.out.println("Product to remove: " + productToRemove);

        productRepository.delete(productToRemove);
        System.out.println("Is product removed? " + !productRepository.existsById(productToRemove.getId()));
    }
}

Beyond Basic: Derived Query Methods

While findById() and findAll() are great, Spring Data JPA offers even more! You can define custom derived query methods directly in your repository interface.

Spring automatically generates the query based on the method name.
For example, findByName(String name) will find products by their name.
This simplifies common read operations without writing SQL!

We'll explore more complex custom queries in a future lesson.

Quick Check: CRUD Actions

Which of the following Spring Data JPA repository methods are used for reading existing data?

Recap: Mastering CRUD

Congratulations! You've learned how to perform the essential CRUD operations using Spring Data JPA. These methods are the backbone of almost any data-driven application.

Create/Update: Use repository.save(entity).
Read: Use repository.findById(id) for single items and repository.findAll() for all items.
Delete: Use repository.deleteById(id) or repository.delete(entity).

With these powerful repository methods, you can efficiently manage your application's data!

よくある質問

「CRUD操作の実行」レッスンは無料ですか？

はい。「CRUD操作の実行」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Spring Boot 4 Microservices & REST APIsコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Spring Boot 4 Microservices & REST APIsコースには全6レッスンが含まれています。

「CRUD操作の実行」で何を学びますか？

Spring Data JPAの強力なリポジトリメソッドを使って、作成、読み取り、更新、削除の操作を実装します。ブラウザで直接実行するハンズオンコードでSpring Boot 4 Microservices & REST APIsを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Spring Boot 4 Microservices & REST APIsを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのSpring Boot 4 Microservices & REST APIsは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン6/6です。

「CRUD操作の実行」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このSpring Boot 4 Microservices & REST APIsレッスンでコードを書いて実行できますか？

はい。すべてのSpring Boot 4 Microservices & REST APIsレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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