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 Groovy.

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.

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide \
   --features=data-jdbc,postgres,flyway \
   --build=maven --lang=groovy
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. Create Entity

Create a @MappedEntity to save persons. Initially, consider name and age required. Use int primitive for the age.

src/main/groovy/example/micronaut/Person.groovy
package example.micronaut

import groovy.transform.CompileStatic
import io.micronaut.core.annotation.NonNull
import io.micronaut.core.annotation.Nullable
import io.micronaut.data.annotation.GeneratedValue
import io.micronaut.data.annotation.Id
import io.micronaut.data.annotation.MappedEntity
import io.micronaut.data.annotation.Version

import javax.validation.constraints.NotBlank

@CompileStatic
@MappedEntity (1)
class Person {

    @Id (2)
    @GeneratedValue (3)
    Long id

    @Version (4)
    Long version

    @NonNull
    @NotBlank
    final String name

    final int age

    Person(@NonNull String name, int age) {
        this.name = name
        this.age = age
    }

}
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.

3.2. 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:

pom.xml
<dependency>
    <groupId>io.micronaut.flyway</groupId>
    <artifactId>micronaut-flyway</artifactId>
    <scope>compile</scope>
</dependency>
<dependency>
    <groupId>org.flywaydb</groupId>
    <artifactId>flyway-mysql</artifactId>
    <scope>runtime</scope>
</dependency>

We will enable Flyway in the application.yml and configure it to perform migration on one of the defined data sources.

src/main/resources/application.yml
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:

src/main/resources/db/migration/V1__create-person.sql
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

id

NO

version

NO

name

NO

age

NO

3.3. Drop Not Null Constraint

Applications change. Make age optional:

src/main/groovy/example/micronaut/Person.groovy
    @Nullable
    final Integer age

    Person(@NonNull String name,
           @Nullable Integer age) {
        this.name = name
        this.age = age
    }

Add a new migration to drop the null constraint:

src/main/resources/db/migration/V2__nullable-age.sql
ALTER TABLE person ALTER COLUMN age DROP NOT NULL;

After the migration, the person table looks like:

Column Nullable

id

NO

version

NO

name

NO

age

YES

4. Flyway endpoint

To enable the Flyway endpoint, add the management dependency on your classpath.

pom.xml
<dependency>
    <groupId>io.micronaut</groupId>
    <artifactId>micronaut-management</artifactId>
    <scope>compile</scope>
</dependency>

Enable the Flyway endpoint:

src/main/resources/application.yml
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:

pom.xml
<dependency>
    <groupId>org.testcontainers</groupId>
    <artifactId>postgresql</artifactId>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.testcontainers</groupId>
    <artifactId>testcontainers</artifactId>
    <scope>test</scope>
</dependency>

Configure the default datasource to use the PostgreSQL database provided by TestContainers for the test environment:

src/test/resources/application-test.yml
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.

src/test/groovy/example/micronaut/FlywayEndpointSpec.groovy
package example.micronaut

import io.micronaut.core.type.Argument
import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpResponse
import io.micronaut.http.client.BlockingHttpClient
import io.micronaut.http.client.HttpClient
import io.micronaut.http.client.annotation.Client
import io.micronaut.test.extensions.spock.annotation.MicronautTest
import jakarta.inject.Inject
import spock.lang.Specification

import static io.micronaut.http.HttpStatus.OK

@MicronautTest (1)
class FlywayEndpointSpec extends Specification {

    @Inject
    @Client('/')  (2)
    HttpClient httpClient

    void migrationsAreExposedViaAndEndpoint() {
        given:
        BlockingHttpClient client = httpClient.toBlocking()

        when:
        HttpResponse<List<FlywayReport>> response = client.exchange(
                HttpRequest.GET('/flyway'),
                Argument.listOf(FlywayReport))

        then:
        OK == response.status()

        when:
        List<FlywayReport> flywayReports = response.body()

        then:
        1 == flywayReports?.size()

        when:
        FlywayReport flywayReport = flywayReports[0]

        then:
        2 == flywayReport?.migrations?.size()
    }

    static class FlywayReport {
        List<Migration> migrations
    }

    static class Migration {

        String script

        void setId(String script) {
            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.

src/main/resources/application.yml
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 ./mvnw mn: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.

You can run a cURL command to test the application:

curl http://localhost:8080/flyway

You will see information about migrations.

5. Next steps

Explore more features with Micronaut Guides.

Check Micronaut Flyway integration.

Learn more about Flyway.

6. Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.