Entity and repository

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Goal

Create the Item JPA entity and the ItemRepository interface. After this page Hibernate will create an item table in H2 on startup and the repository gives you full CRUD access to it.

Prerequisites

• Add JPA and H2

The Item entity

Create src/main/java/com/example/itemsapi/Item.java:

package com.example.itemsapi;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.validation.constraints.NotBlank;

@Entity
public class Item {

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

    @NotBlank
    private String name;

    // getters and setters
    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; }
}

Key annotations:

• @Entity — tells JPA that this class maps to a database table. Hibernate derives the table name from the class name: item.
• @Id — marks the primary key field.
• @GeneratedValue(strategy = GenerationType.IDENTITY) — tells the database to auto-increment the id column. H2 supports this natively.
• @NotBlank — a Bean Validation constraint. It rejects null, empty strings, and strings that contain only whitespace. Validation is triggered by @Valid in the controller (page 05).

We use a plain class with getters and setters rather than a record because JPA requires a no-argument constructor and mutable fields. Spring Boot 3.x uses Jakarta imports (not javax.persistence).

The ItemRepository interface

Create src/main/java/com/example/itemsapi/ItemRepository.java:

package com.example.itemsapi;

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

public interface ItemRepository extends JpaRepository<Item, Long> { }

JpaRepository<Item, Long> provides:

Method	What it does
save(item)	Insert or update
findAll()	Return all rows
findById(id)	Return Optional<Item>
deleteById(id)	Delete by primary key

You write zero implementation code. Spring Data generates a proxy at startup that implements the interface against your H2 datasource.

Verify: project compiles

./mvnw compile

Expected output:

BUILD SUCCESS

Hibernate also logs the DDL it generates at startup (visible with spring-boot:run). You will see a create table item statement when the app starts — confirming the entity is wired up.

Next → Service layer