Database migration với Flyway trong Spring Boot hoạt động thế nào?

Flyway quản lý database schema migration dưới dạng versioned SQL files — rollback, audit trail, reproducible schema.

<dependency>
  <groupId>org.flywaydb</groupId>
  <artifactId>flyway-core</artifactId>
</dependency>

Tạo migration script:

src/main/resources/db/migration/
  V1__create_users_table.sql
  V2__add_email_index.sql
  V3__add_profile_table.sql

Naming convention: V{version}__{description}.sql

-- V1__create_users_table.sql
CREATE TABLE users (
  id BIGSERIAL PRIMARY KEY,
  email VARCHAR(255) UNIQUE NOT NULL,
  created_at TIMESTAMP DEFAULT NOW()
);

Spring Boot auto-run: Flyway tự chạy khi app startup — apply tất cả pending migration theo thứ tự version.

spring:
  flyway:
    locations: classpath:db/migration
    baseline-on-migrate: true   # khi DB đã có schema cũ
    validate-on-migrate: true   # checksum mismatch → fail

Flyway lưu trạng thái trong bảng flyway_schema_history — biết migration nào đã chạy.

Không sửa migration đã chạy — checksum thay đổi → Flyway fail. Tạo file mới V4__alter_... thay thế.

Vs Liquibase: Flyway đơn giản hơn (SQL thuần), Liquibase flexible hơn (YAML/XML, rollback tốt hơn).

Flyway manages database schema migrations as versioned SQL files — rollbacks, audit trail, reproducible schemas.

<dependency>
  <groupId>org.flywaydb</groupId>
  <artifactId>flyway-core</artifactId>
</dependency>

Creating migration scripts:

src/main/resources/db/migration/
  V1__create_users_table.sql
  V2__add_email_index.sql
  V3__add_profile_table.sql

Naming convention: V{version}__{description}.sql

-- V1__create_users_table.sql
CREATE TABLE users (
  id BIGSERIAL PRIMARY KEY,
  email VARCHAR(255) UNIQUE NOT NULL,
  created_at TIMESTAMP DEFAULT NOW()
);

Spring Boot auto-run: Flyway runs on app startup — applies all pending migrations in version order.

spring:
  flyway:
    locations: classpath:db/migration
    baseline-on-migrate: true   # when an existing schema is already present
    validate-on-migrate: true   # checksum mismatch → fail fast

Flyway tracks state in the flyway_schema_history table — knows which migrations have run.

Never edit a migration that has already run — checksum changes → Flyway fails. Create a new V4__alter_... file instead.

Flyway vs Liquibase: Flyway is simpler (plain SQL), Liquibase is more flexible (YAML/XML, better rollbacks).