mn create-app example.micronaut.micronautguide \
--features=data-jdbc,postgres,flyway \
--build=gradle --lang=kotlin
Schema Migration with Flyway
Learn how to use Flyway to manage your schema migrations
Authors: Sergio del Amo
Micronaut Version: 3.5.2
1. Getting Started
In this guide, we will create a Micronaut application written in Kotlin.
You use Flyway:
Flyway is an open-source database migration tool. It strongly favors simplicity and convention over configuration.
2. What you will need
To complete this guide, you will need the following:
-
Some time on your hands
-
A decent text editor or IDE
-
JDK 1.8 or greater installed with
JAVA_HOME
configured appropriately
3. Solution
We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.
-
Download and unzip the source
Create an application using the Micronaut Command Line Interface or with Micronaut Launch.
If you don’t specify the --build argument, Gradle is used as the build tool. If you don’t specify the --lang argument, Java is used as the language.
|
The previous command creates a Micronaut application with the default package example.micronaut
in a directory named micronautguide
.
If you use Micronaut Launch, select "Micronaut Application" as application type and add postgres , data-jdbc , and flyway as features.
|
3.1. Enable annotation Processing
If you use Java or Kotlin and IntelliJ IDEA, make sure to enable annotation processing.

3.2. Create Entity
Create a @MappedEntity
to save persons. Initially, consider name and age required. Use int
primitive for the age.
package example.micronaut
import io.micronaut.data.annotation.GeneratedValue
import io.micronaut.data.annotation.Id
import io.micronaut.data.annotation.MappedEntity
import io.micronaut.data.annotation.Version
@MappedEntity (1)
class Person(
val name: String,
val age: Int
) {
@Id (2)
@GeneratedValue (3)
var id: Long? = null
@Version (4)
var version: Long? = null
}
1 | Annotate the class with @MappedEntity to map the class to the table defined in the schema. |
2 | Specifies the ID of an entity |
3 | Specifies that the property value is generated by the database and not included in inserts |
4 | Annotate the field with @Version to enable optimistic locking for your entity. |
3.3. Database Migration with Flyway
We need a way to create the database schema. For that, we use Micronaut integration with Flyway.
Flyway automates schema changes, significantly simplifying schema management tasks, such as migrating, rolling back, and reproducing in multiple environments.
Add the following snippet to include the necessary dependencies:
implementation("io.micronaut.flyway:micronaut-flyway")
runtimeOnly("org.flywaydb:flyway-mysql")
We will enable Flyway in the application.yml
and configure it to perform migration on one of the defined data sources.
flyway:
datasources:
default:
enabled: true (1)
1 | Enable Flyway for the default datasource. |
Configuring multiple data sources is as simple as enabling Flyway for each one. You can also specify folders that will be used for migrating each data source. Review the Micronaut Flyway documentation for additional details. |
Flyway migration will be automatically triggered before your Micronaut application starts. Flyway will read migration commands in the resources/db/migration/
directory, execute them if necessary, and verify that the configured data source is consistent with them.
Create the following migration files with the database schema creation:
CREATE TABLE person(
id bigint primary key not null,
name varchar(255) not null,
age int not null
)
During application startup, Flyway executes the SQL file and creates the schema needed for the application.
If you check the database schema, there are two tables:
-
person
-
flyway_scheme_history
Flyway uses the table flyway_scheme_history
to keep track of database migrations.
The person
table looks like:
Column | Nullable |
---|---|
|
NO |
|
NO |
|
NO |
|
NO |
3.4. Drop Not Null Constraint
Applications change. Make age
optional:
val age: Int?
Add a new migration to drop the null constraint:
ALTER TABLE person ALTER COLUMN age DROP NOT NULL;
After the migration, the person
table looks like:
Column | Nullable |
---|---|
|
NO |
|
NO |
|
NO |
|
YES |
4. Flyway endpoint
To enable the Flyway endpoint, add the management
dependency on your classpath.
implementation("io.micronaut:micronaut-management")
Enable the Flyway endpoint:
endpoints:
flyway:
enabled: true
sensitive: false
4.1. Testing with PostgreSQL via TestContainers
We use Test Containers to test against a PostgreSQL database.
Add the following snippet to include the necessary test container dependencies:
testImplementation("org.testcontainers:postgresql")
testImplementation("org.testcontainers:testcontainers")
Configure the default datasource to use the PostgreSQL database provided by TestContainers for the test environment:
datasources:
default:
url: jdbc:tc:postgresql:12:///postgres (1)
driverClassName: org.testcontainers.jdbc.ContainerDatabaseDriver
1 | By using a specially modified JDBC URL, Testcontainers provides a disposable stand-in database that can be used without requiring modification to your application code. See Test Containers JDBC URL. |
4.2. Test
Create a test that invokes the Flyway endpoint.
package example.micronaut
import io.micronaut.core.type.Argument
import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpStatus.OK
import io.micronaut.http.client.HttpClient
import io.micronaut.http.client.annotation.Client
import io.micronaut.test.extensions.junit5.annotation.MicronautTest
import jakarta.inject.Inject
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Assertions.assertNotNull
import org.junit.jupiter.api.Test
@MicronautTest (1)
class FlywayEndpointTest {
@Inject
@field:Client("/")
lateinit var httpClient: HttpClient (2)
@Test
fun migrationsAreExposedViaAndEndpoint() {
val client = httpClient.toBlocking()
val response = client.exchange(HttpRequest.GET<Any>("/flyway"), Argument.listOf(FlywayReport::class.java))
assertEquals(OK, response.status())
val flywayReports = response.body()
assertNotNull(flywayReports)
assertEquals(1, flywayReports!!.size)
val flywayReport = flywayReports[0]
assertNotNull(flywayReport)
assertNotNull(flywayReport.migrations)
assertEquals(2, flywayReport.migrations!!.size)
}
internal class FlywayReport {
var migrations: List<Migration>? = null
}
internal class Migration {
var script: String? = null
private set
fun setId(script: String?) {
this.script = script
}
}
}
1 | Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context and the embedded server. More info. |
2 | Inject the HttpClient bean and point it to the embedded server. |
4.3. Running the application
After installing Docker, execute the following command to run a PostgreSQL container:
docker run -it --rm \
-p 5432:5432 \
-e POSTGRES_USER=dbuser \
-e POSTGRES_PASSWORD=theSecretPassword \
-e POSTGRES_DB=postgres \
postgres:11.5-alpine
Set up the following environment variables to connect to the PostgreSQL database you started with Docker.
datasources:
default:
url: jdbc:postgresql://localhost:5432/postgres (1)
driverClassName: org.postgresql.Driver (2)
dialect: POSTGRES (3)
schema-generate: NONE (4)
1 | The JDBC URL matches the database name you used in the previous command. |
2 | Use PostgreSQL driver. |
3 | Configure the PostgreSQL dialect. |
4 | You handle database migrations via Flyway. |
export DATASOURCES_DEFAULT_USERNAME=dbuser
export DATASOURCES_DEFAULT_PASSWORD=theSecretPassword
Configure your default datasource to use the PostgreSQL database you started with Docker:
To run the application, use the ./gradlew run
command, which starts the application on port 8080.
You can run a cURL command to test the application:
curl http://localhost:8080/flyway
You will see information about migrations.
5. Generate a Micronaut Application Native Image with GraalVM
We will use GraalVM, the polyglot embeddable virtual machine, to generate a native image of our Micronaut application.
Compiling native images ahead of time with GraalVM improves startup time and reduces the memory footprint of JVM-based applications.
Only Java and Kotlin projects support using GraalVM’s native-image tool. Groovy relies heavily on reflection, which is only partially supported by GraalVM.
|
5.1. Native image generation
The easiest way to install GraalVM on Linux or Mac is to use SDKMan.io.
sdk install java 22.1.0.r11-grl
If you still use Java 8, use the JDK11 version of GraalVM. |
sdk install java 22.1.0.r17-grl
For installation on Windows, or for manual installation on Linux or Mac, see the GraalVM Getting Started documentation.
After installing GraalVM, install the native-image
component, which is not installed by default:
gu install native-image
To generate a native image using Gradle, run:
./gradlew nativeCompile
The native image is created in build/native/nativeCompile
directory and can be run with build/native/nativeCompile/micronautguide
.
It is possible to customize the name of the native image or pass additional parameters to GraalVM:
graalvmNative {
binaries {
main {
imageName.set('mn-graalvm-application') (1)
buildArgs.add('--verbose') (2)
}
}
}
1 | The native image name will now be mn-graalvm-application |
2 | It is possible to pass extra arguments to build the native image |
You can run a cURL command to test the application:
curl http://localhost:8080/flyway
You will see information about migrations.
6. Next steps
Explore more features with Micronaut Guides.
Check Micronaut Flyway integration.
Learn more about Flyway.
7. Help with the Micronaut Framework
The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.