Evaluating Grails version compatibility and abstracting Flyway integration steps under output constraints.Detailing concrete Grails project files and startup migration wiring for a minimal Flyway hello-world.Shifting from plugin to manual flyway-core and wiring migration execution before Hibernate via BootStrap or resources.groovy.Evaluating plugin versus manual Flyway setup and choosing BootStrap wiring for explicit migration ordering.Expanding the answer with full file tree, code blocks, and troubleshooting notes for Flyway integration. Here's a minimal, working **Grails (Groovy) Hello World + Flyway** setup. It uses H2 so you can run immediately, with Postgres notes. ### 1. What you'll build ``` hello-world/ ├── build.gradle ├── grails-app/controllers/helloworld/HelloController.groovy ├── grails-app/domain/helloworld/Greeting.groovy ├── grails-app/conf/application.yml ├── grails-app/init/helloworld/BootStrap.groovy ├── grails-app/views/hello/index.gsp └── src/main/resources/db/migration/ ├── V1__create_greeting_table.sql └── V2__insert_hello_data.sql ``` Create it: ```bash sdk install java 17-tem sdk install grails grails create-app hello-world --profile=web --package=helloworld cd hello-world ``` ### 2. Add Flyway dependency In `build.gradle`: ```groovy dependencies { // ... keep grails stuff implementation "org.flywaydb:flyway-core:9.22.3" runtimeOnly "com.h2database:h2" // for Postgres instead, use: // runtimeOnly "org.postgresql:postgresql:42.6.0" } ``` > Use Flyway 9.x for Grails 5/6. Flyway 10+ needs Spring Boot 3 / Grails 7. ### 3. Disable Hibernate auto-DDL, configure DataSource This is critical. Flyway must own the schema. `grails-app/conf/application.yml`: ```yaml dataSource: pooled: true jmxExport: true driverClassName: org.h2.Driver dialect: org.hibernate.dialect.H2Dialect username: sa password: '' environments: development: dataSource: dbCreate: none url: jdbc:h2:mem:devDb;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE test: dataSource: dbCreate: none url: jdbc:h2:mem:testDb;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE production: dataSource: dbCreate: none url: jdbc:h2:./prodDb;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE flyway: enabled: true locations: classpath:db/migration ``` For Postgres, replace with: ```yaml dataSource: driverClassName: org.postgresql.Driver dialect: org.hibernate.dialect.PostgreSQLDialect username: postgres password: postgres environments: development: dataSource: dbCreate: none url: jdbc:postgresql://localhost:5432/hello ``` ### 4. Create Domain + Controller `grails-app/domain/helloworld/Greeting.groovy`: ```groovy package helloworld class Greeting { String message Date dateCreated static constraints = { message blank: false, maxSize: 255 } } ``` `grails-app/controllers/helloworld/HelloController.groovy`: ```groovy package helloworld class HelloController { def index() { def greeting = Greeting.first() ?: new Greeting(message: 'Hello, World!') [greeting: greeting] } def json() { respond Greeting.list() } } ``` `grails-app/views/hello/index.gsp`: ```gsp Hello

${greeting.message}

Loaded from DB via Flyway + GORM. Count: ${helloworld.Greeting.count()}

View as JSON ``` Map `/` to it in `grails-app/controllers/helloworld/UrlMappings.groovy`: ```groovy static mappings = { "/"(controller: 'hello', action: 'index') "/$controller/$action?/$id?(.$format)?" { constraints {} } } ``` ### 5. Add Flyway migrations `src/main/resources/db/migration/V1__create_greeting_table.sql`: ```sql CREATE TABLE greeting ( id BIGINT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY, version BIGINT NOT NULL, message VARCHAR(255) NOT NULL, date_created TIMESTAMP NOT NULL ); ``` This syntax works on both H2 and Postgres 10+. `src/main/resources/db/migration/V2__insert_hello_data.sql`: ```sql INSERT INTO greeting (version, message, date_created) VALUES (0, 'Hello, World from Flyway!', CURRENT_TIMESTAMP); ``` ### 6. Hook Flyway into startup `grails-app/init/helloworld/BootStrap.groovy`: ```groovy package helloworld import grails.core.GrailsApplication import org.flywaydb.core.Flyway import javax.sql.DataSource class BootStrap { GrailsApplication grailsApplication DataSource dataSource def init = { servletContext -> def cfg = grailsApplication.config.getProperty('flyway', Map, [:]) if (cfg.enabled != false) { Flyway.configure() .dataSource(dataSource) .locations((cfg.locations ?: 'classpath:db/migration') as String[]) .baselineOnMigrate(true) .load() .migrate() } } def destroy = { } } ``` > For Hello World this is enough (`dbCreate: none` means Hibernate won't fail at startup if tables don't exist yet). For production ordering (Flyway before Hibernate), use the `org.grails.plugins:flyway` plugin which adds a `sessionFactory dependsOn flyway` bean. ### 7. Run ```bash ./gradlew bootRun ``` Visit: * `http://localhost:8080/` -> `Hello, World from Flyway!` * `http://localhost:8080/hello/json` -> JSON list Check Flyway ran: ```sql SELECT * FROM flyway_schema_history; -- should show V1, V2 as SUCCESS ``` When you need a new change, just add `V3__...sql` and restart — no `dbCreate: update` ever again.

groovy grails hello world app with flyway integration