These tutorials target Micronaut Framework 3. Read, Guides for Micronaut Framework 4.

Table of Contents

Schema Migration with Liquibase

Learn how to use the Liquibase to manage your schema migrations.

Authors: Sergio del Amo

Micronaut Version: 3.9.2

1. Getting Started

In this guide, we will create a Micronaut application written in Java.

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,liquibase \
   --build=gradle \
   --lang=java \
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 liquibase as features.

Setup IntelliJ IDEA to develop Micronaut Applications.

3.1. Create Entity

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

src/main/java/example/micronaut/Person.java
package example.micronaut;

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;

@MappedEntity (1)
public class Person {

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

    @Version (4)
    private Long version;

    @NonNull
    @NotBlank
    private final String name;

    private final int age;

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

    public int getAge() {
        return age;
    }


    @NonNull
    public String getName() {
        return name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Long getVersion() {
        return version;
    }

    public void setVersion(Long version) {
        this.version = version;
    }
}
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 Liquibase

We need a way to create the database schema. For that, we use Micronaut integration with Liquibase.

Add the following snippet to include the necessary dependencies:

build.gradle
implementation("io.micronaut.liquibase:micronaut-liquibase")

Configure the database migrations directory for Liquibase in application.yml.

src/main/resources/application.yml
liquibase:
  enabled: true
  datasources:
    default:
      change-log: 'classpath:db/liquibase-changelog.xml'

Create the following files with the database schema creation:

src/main/resources/db/liquibase-changelog.xml
<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog
    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.1.xsd">

    <include file="changelog/01-create-person.xml"
             relativeToChangelogFile="true"/>

    <include file="changelog/02-nullable-age.xml"
             relativeToChangelogFile="true"/>

</databaseChangeLog>
src/main/resources/db/changelog/01-create-person.xml
<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog
    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.1.xsd">

    <changeSet id="01" author="sdelamo">

        <createTable tableName="person"
                     remarks="A table to contain persons">

            <column name="id" type="BIGINT">
                <constraints nullable="false"
                             unique="true"
                             primaryKey="true"
                             primaryKeyName="personPK"/>
            </column>

            <column name="version" type="BIGINT">
                <constraints nullable="false"/>
            </column>

            <column name="age" type="INT">
                <constraints nullable="false"/>
            </column>

        </createTable>

    </changeSet>

</databaseChangeLog>

During application startup, Liquibase executes the SQL file and creates the schema needed for the application.

If you check the database schema, there are three tables:

  • databasechangelog

  • databasechangeloglock

The tables databasechangelog and databasechangeloglock are used by Liquibase 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/java/example/micronaut/Person.java
    @Nullable
    private final Integer age;

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

    @Nullable
    public Integer getAge() {
        return age;
    }

Add a new changeset to drop the null constraint:

src/main/resources/db/liquibase-changelog.xml
<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog
    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.1.xsd">

    <include file="changelog/01-create-person.xml"
             relativeToChangelogFile="true"/>

    <include file="changelog/02-nullable-age.xml"
             relativeToChangelogFile="true"/>

</databaseChangeLog>
src/main/resources/db/changelog/02-nullable-age.xml
<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog
    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.1.xsd">

    <changeSet id="02" author="sdelamo">
        <dropNotNullConstraint tableName="person"
                               columnName="age"/>
    </changeSet>

</databaseChangeLog>

After the changeset, the person table looks like:

Column Nullable

id

NO

version

NO

name

NO

age

YES

4. Liquibase

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

build.gradle
implementation("io.micronaut:micronaut-management")

Enable the Liquibase endpoint:

src/main/resources/application.yml
endpoints:
  liquibase:
    enabled: true
    sensitive: false

5. Test Resources

When the application is started locally — either under test or by running the application — resolution of the datasource URL is detected and the Test Resources service will start a local PostgreSQL docker container, and inject the properties required to use this as the datasource.

For more information, see the JDBC section of the Test Resources documentation.

5.1. Test

Create a test that invokes the Liquibase endpoint

src/test/java/example/micronaut/LiquibaseEndpointTest.java
package example.micronaut;

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.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;

import java.util.List;

import static io.micronaut.http.HttpStatus.OK;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;

@MicronautTest (1)
public class LiquibaseEndpointTest {

    @Inject
    @Client("/")  (2)
    HttpClient httpClient;

    @Test
    void migrationsAreExposedViaAndEndpoint() {
        BlockingHttpClient client = httpClient.toBlocking();

        HttpResponse<LiquibaseReport> response = client.exchange(
                HttpRequest.GET("/liquibase"),
                LiquibaseReport.class);
        assertEquals(OK, response.status());

        LiquibaseReport liquibaseReport = response.body();
        assertNotNull(liquibaseReport);
        assertNotNull(liquibaseReport.getChangeSets());
        assertEquals(2, liquibaseReport.getChangeSets().size());
    }

    static class LiquibaseReport {

        private List<ChangeSet> changeSets;

        public void setChangeSets(List<ChangeSet> changeSets) {
            this.changeSets = changeSets;
        }

        public List<ChangeSet> getChangeSets() {
            return changeSets;
        }
    }

    static class ChangeSet {

        private String id;

        public void setId(String id) {
            this.id = id;
        }

        public String getId() {
            return id;
        }
    }
}
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.

5.2. Running the application

Although the URL is configured automatically via Test Resources, we must configure the PostgreSQL driver and dialect in application.yml:

src/main/resources/application.yml
datasources:
  default:
    driverClassName: org.postgresql.Driver  (1)
    dialect: POSTGRES (2)
    schema-generate: NONE (3)
1 Use PostgreSQL driver.
2 Configure the PostgreSQL dialect.
3 You handle database migrations via Liquibase

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/liquibase

You will see information about migrations.

6. Generate a Micronaut Application Native Executable with GraalVM

We will use GraalVM, the polyglot embeddable virtual machine, to generate a native executable of our Micronaut application.

Compiling native executables 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.

6.1. Native executable generation

The easiest way to install GraalVM on Linux or Mac is to use SDKMan.io.

Java 11
sdk install java 22.3.r11-grl
If you still use Java 8, use the JDK11 version of GraalVM.
Java 17
sdk install java 22.3.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 executable using Gradle, run:

./gradlew nativeCompile

The native executable 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 executable or pass additional parameters to GraalVM:

build.gradle
graalvmNative {
    binaries {
        main {
            imageName.set('mn-graalvm-application') (1)
            buildArgs.add('--verbose') (2)
        }
    }
}
1 The native executable name will now be mn-graalvm-application
2 It is possible to pass extra arguments to build the native executable

You can run a cURL command to test the application:

curl http://localhost:8080/liquibase

You will see information about migrations.

7. Next steps

Explore more features with Micronaut Guides.

Check Micronaut Liquibase integration.

8. Help with the Micronaut Framework

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