Simplify Java persistence implementation with Kotlin on Quarkus

For decades, developers have struggled with optimizing persistence layer implementation in terms of storing business data, retrieving relevant data quickly, and—most importantly— simplifying data transaction logic regardless of programming languages.

Fortunately, this challenge triggered the invention of Java ecosystems in which developers can implement the Java Persistence API (JPA). For instance, Hibernate Object Relational Mapper (ORM) with Panache is the standard framework for JPA implementation in the Java ecosystem.

Kotlin is a programming language designed to run business applications with multiple programming languages on top of Java Virtual Machine (JVM) for the Java persistence implementation. But there's still the hurdle for Java developers to catch up on the new syntax and JPA APIs of Kotlin.

This article will explain how Quarkus makes it easier for developers to implement Kotlin applications through the Quarkus Hibernate ORM Panache Kotlin extension.

Create a new Hibernate ORM Kotlin project using Quarkus CLI

First, create a new Maven project using the Quarkus command-line tool (CLI). The following command will add Quarkus extensions to enable Hibernate ORM Panache Kotlin and PostgreSQL JDBC extensions:

$ quarkus create app hibernate-kotlin-example \
 -x jdbc-postgresql, hibernate-orm-panache-kotlin

The output should look like this:

...
<[SUCCESS] ✅ quarkus project has been successfully generated in:
--> /Users/danieloh/Downloads/demo/hibernate-kotlin-example
...

Create a new entity and repository

Hibernate ORM with Panache enables developers to handle entities with active record patterns with the following benefits:

• Auto-generation of IDs
• No need for getters/setters
• Super useful static methods for access such as listAll() and find()
• No need for custom queries for basic operations (e.g. Person.find ("name", "daniel"))

Kotlin doesn't support the Hibernate ORM with Panache in the same way Java does. Instead, Quarkus allows developers to bring these capabilities into Kotlin using the companion object, as illustrated below:

@Entity(name = "Person")
class Person : PanacheEntity() {
lateinit var name: String
}

Here is a simple example of how developers can implement PanacheRepository to access the entity:

@ApplicationScoped
class PersonRepository: PanacheRepository<Person> {
fun findByName(name: String) = find("name", name).firstResult()
}

Super simple! Now I'll show you how to implement resources to access data by RESTful APIs.

Create a resource to handle RESTful APIs

Quarkus fully supports context and dependency injection (CDI), which allows developers to inject PersonRepository to access the data (e.g., findByName(name)) in the resources. For example:

@Inject
lateinit var personRepository: PersonRepository

@GET
@Produces(MediaType.TEXT_PLAIN)
@Path("/{name}")
fun greeting(@PathParam("name") name: String): String {
return "Hello ${personRepository.findByName(name)?.name}"
}

Run and test the application

As always, run your Quarkus application using Developer Mode:

$ cd hibernate-kotlin-example
$ quarkus dev

The output should look like this:

...
INFO [io.quarkus] (Quarkus Main Thread) Profile dev activated. \
Live Coding activated.
INFO [io.quarkus] (Quarkus Main Thread) \
Installed features: [agroal, cdi, hibernate-orm, \
hibernate-orm-panache-kotlin, jdbc-postgresql, \
kotlin, narayana-jta, resteasy, smallrye-context-propagation, vertx]

--
Tests paused
Press [r] to resume testing, [o] Toggle test output, \
[:] for the terminal, [h] for more options>

Quarkus Dev services stand up a relevant database container automatically when you run a container runtime (e.g., Docker or Podman) and add a database extension. In this example, I already added the jdbc-postgresql extension, so a PostgreSQL container will be running automatically when the Quarkus Dev mode begins. Find the solution in my GitHub repository.

Access the RESTful API (/hello) to retrieve the data by the name parameter. Execute the following curl command line in your local terminal:

& curl localhost:8080/hello/Daniel

The output should look like this:

Hello Daniel

Conclusion

This is a basic explanation of how Quarkus enables developers to simplify JPA implementation using Kotlin programming APIs for reactive Java applications. Developers can also have better developer experiences, such as dev services and live coding, while they keep developing with Kotlin programming in Quarkus. For more information about Quarkus, visit the Quarkus web page.