Introduction
I have lately written a short tutorial on Building REST services with Spring Boot, JPA and MySQL, with Part 1 and Part 2.I decided to add an essential part to any serious project with an SQL store: management of Database Migrations.
In a real world where requirements will change, or when schemas cannot be fully designed up front, you will be facing a real problem sooner than later: how to manage changes in Database schema, once the application or web service is running?
I wrote an article some time ago, which still seems to be quite valid. You can read there the details of a recommended development workflow to cope with Database migrations in all phases of development.
In this article, I will apply the same ideas from my previous article to a more up-to-date app: a Spring Boot Rest Web service with MySQL.
Adding the Liquibase plug-in for Maven
Let's add the Liquibase plug-in.What we want to achieve at this first step is to be able to evolve our model and keep working as before adding Liquibase: the Hibernate Maven plugin will take care of recreating the schema up-to-date every time we run tests or lunch the application.
We add the dependency:
Our initial Liquibase changeset will be empty.
We need to add the Database Changelog File for liquibase: the file where all changes managed by Liquibase are registered. It will initially be empty.
We add the file src/main/resources/db/db.changelog.xml:
We add the liquibase.properties file:
We finally add the plug-in with relevant configuration:
With this configuration, we are telling Liquibase not to try any database migrations. This is our normal workflow of updating model with JPA annotations and running tests. Hibernate plugin takes care of dropping and re-creating the database.
This is what we see if we run mvn clean test
Generating DB diff automatically with Liquibase: First migration
We have finished evolving our model and adding the additional logic and tests.We are now happy and ready to commit a change.
This point could even be the very first version of your DB schema!
Let's generate the DB diff with Liquibase.
The generated diff file will be incorporated to the registered Liquibase DB schema updates. Additionally, when running our app, Liquibase will take care of migrating the DB schema to the latest version registered in our codebase.
To make all this magic happen, let's add a profile in our pom file so we can generate the DB diff anytime.
Let's generate our first Liquibase migration with mvn clean process-test-resources -Pdb-diff:
Liquibase has generated for us the file src/main/resources/db/db-20170709_144112.changelog.xml with this contents:
Great! We can now add this filename to our global DB changelog file:
Subsequent migrations with Liquibase
To check our migration mechanism works well, let's update our model with a version field and generate again a DB diff via mvn process-test-resources -Pdb-diff.Liquibase generates this file:
This seems like magic!
Automatic DB migration embedded in the app
Having added liquibase in our dependencies has also included a Liquibase Spring Bean to our app. This bean runs at application startup, checks the registered changesets against the app DB and brings the DB schema up-to-date automatically by applying any needed migrations.It would be good to see this in action at development time, so we can test it.
Let's add another profile to our maven project for this.
This profiles skips any schema generation by the Hibernate plugin and drops the database. This way, when the app starts, the Liquibase Spring bean will enter into action and be forced to run all registered migrations.
If we now run the app via mvn clean spring-boot:run -Pdb-test:
Works as expected!
Source Code and Additional Info
Source code for this tutorial here.Additional Liquibase maven plugin info: mvn liquibase:help
More info about Liquibase here.
Some more info in my previous article about DB migration.
