Spring Boot + JPA + Hibernate: Database Made Easy

In Week 3, we built REST APIs with controllers, DTOs, validation, and CRUD operations.
Now, in Week 4, it’s time to connect your APIs to a real database using Spring Data JPA and Hibernate, and understand entity relationships, queries, and performance best practices.

What is JPA and Hibernate?

JPA (Java Persistence API) is a standard interface for working with relational databases in Java.
Hibernate is the most popular JPA implementation, providing extra features like caching, lazy loading, and advanced queries.

Think of JPA as the contract and Hibernate as the implementation.

Why Use Spring Data JPA?

Spring Data JPA simplifies database access by:

• Auto-generating queries

• Handling boilerplate CRUD code

• Supporting pagination and sorting

• Integrating seamlessly with Spring Boot

Step 1: Add Dependencies

In your pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <scope>runtime</scope>
</dependency>

<!-- Optional: MySQL/PostgreSQL -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

Start with H2 (in-memory DB) for development. Switch to MySQL/PostgreSQL for production.

Step 2: Configure Database

application.yml example:

spring:
  datasource:
    url: jdbc:h2:mem:testdb
    driver-class-name: org.h2.Driver
    username: sa
    password:
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true

ddl-auto: update automatically creates tables based on your entities. Use validate in production.

Step 3: Create Entities & Relationships

User Entity