# Setting Up JPA with Spring Boot — Hibernate / JPA

Source: https://www.skillbyai.com/en/hibernate-jpa/f-setup

> Configure a datasource, Hibernate and schema migrations in a Spring Boot project.

## Dependencies, configuration and schema management

In a Spring Boot application, adding **`spring-boot-starter-data-jpa`** and a JDBC driver (for example PostgreSQL) brings in Hibernate, Spring Data JPA, transaction management and the **HikariCP** connection pool. Configure the datasource URL, user and password in `application.yml`. The property **`spring.jpa.hibernate.ddl-auto`** controls whether Hibernate creates or changes tables: `create-drop` and `update` are tempting in tutorials but dangerous in production, because they cannot express data migrations, may drop or miss changes and differ between environments. In real projects, set it to **`validate`** (Hibernate checks the mapping matches the schema) or `none`, and manage the schema with a **migration tool** such as **Flyway** or **Liquibase**: versioned SQL scripts applied in order, reviewed like code. Turn on SQL logging in development to see exactly what Hibernate does. Spring Boot enables **open session in view** by default (`spring.jpa.open-in-view=true`) with a warning; disabling it is generally recommended, as discussed later.

## application.yml and a Flyway migration

Hibernate validates the schema; Flyway owns it.

```yaml
spring:
  datasource:
    url: jdbc:postgresql://localhost:5432/shop
    username: shop
    password: ${DB_PASSWORD}
  jpa:
    open-in-view: false
    hibernate:
      ddl-auto: validate            # never create/update in production
    properties:
      hibernate:
        jdbc.batch_size: 50
        order_inserts: true
        order_updates: true
  flyway:
    enabled: true

logging:
  level:
    org.hibernate.SQL: debug                          # SQL statements
    org.hibernate.orm.jdbc.bind: trace                # bound parameter values (Hibernate 6+)

# src/main/resources/db/migration/V1__create_customers.sql
# CREATE SEQUENCE customers_seq START WITH 1 INCREMENT BY 50;
# CREATE TABLE customers (
#   id    BIGINT PRIMARY KEY,
#   name  VARCHAR(100) NOT NULL,
#   email VARCHAR(255) NOT NULL UNIQUE
# );
```

## An architect versus a renovator

`ddl-auto=update` is a renovator who changes your house without drawings: fine for a tent, risky for a building people live in. Flyway migrations are numbered architectural drawings, reviewed and applied in order.

**Quiz:** What is a safe setting for spring.jpa.hibernate.ddl-auto in production?

- [ ] create-drop
- [ ] update
- [ ] create
- [x] validate (with Flyway or Liquibase managing the schema)

*Answer:* validate (with Flyway or Liquibase managing the schema). validate checks the mapping without changing the schema; migrations are handled by a dedicated tool.