Simplified MongoDB with Panache and Kotlin

MongoDB is a well known NoSQL Database that is widely used. MongoDB with Panache offers a new layer atop this familiar framework. This guide will not dive in to the specifics of either as those are already covered in the MongoDB with Panache guide. In this guide, we’ll cover the Kotlin specific changes needed to use MongoDB with Panache in your Kotlin-based Quarkus applications.

First: an example

As we saw in the MongoDB with Panache guide, it allows us to extend the functionality in our entities and repositories (also known as DAOs) with some automatically provided functionality. When using Kotlin, the approach is very similar to what we see in the Java version with a slight change or two. To Panache-enable your entity, you would define it something like:

class Person: PanacheMongoEntity {
    lateinit var name: String
    lateinit var birth: LocalDate
    lateinit var status: Status
}

As you can see our entities remain simple. There is, however, a slight difference from the Java version. The Kotlin language doesn’t support the notion of static methods in quite the same way as Java does. Instead, we must use a companion object:

class Person : PanacheMongoEntity() {
    companion object: PanacheMongoCompanion<Person> {  (1)
        fun findByName(name: String) = find("name", name).firstResult()
        fun findAlive() = list("status", Status.Alive)
        fun deleteStefs() = delete("name", "Stef")
    }

    lateinit var name: String  (2)
    lateinit var birth: LocalDate
    lateinit var status: Status
}

1	The companion object holds all the methods not related to a specific instance allowing for general management and querying bound to a specific type.
2	Here there are options, but we’ve chosen the `lateinit` approach. This allows us to declare these fields as non-null knowing they will be properly assigned either by the constructor (not shown) or by the MongoDB POJO codec loading data from the database.

These types differ from the Java types mentioned in those tutorials. For Kotlin support, all the Panache types will be found in the io.quarkus.mongodb.panache.kotlin package. This subpackage allows for the distinction between the Java and Kotlin variants and allows for both to be used unambiguously in a single project.

In the Kotlin version, we’ve simply moved the bulk of the active record pattern functionality to the companion object. Apart from this slight change, we can then work with our types in ways that map easily from the Java side of world.

Using the repository pattern

Defining your entity

When using the repository pattern, you can define your entities as regular POJO.

class Person {
    var id: ObjectId? = null; // used by MongoDB for the _id field
    lateinit var name: String
    lateinit var birth: LocalDate
    lateinit var status: Status
}

Defining your repository

When using Repositories, you get the exact same convenient methods as with the active record pattern, injected in your Repository, by making them implement PanacheMongoRepository:

@ApplicationScoped
class PersonRepository: PanacheMongoRepository<Person> {
     fun findByName(name: String) = find("name", name).firstResult()
     fun findAlive() = list("status", Status.Alive)
     fun deleteStefs() = delete("name", "Stef")
}

All the operations that are defined on PanacheMongoEntityBase are available on your repository, so using it is exactly the same as using the active record pattern, except you need to inject it:

@Inject
lateinit var personRepository: PersonRepository

@GET
fun count() = personRepository.count()

Most useful operations

Once you have written your repository, here are the most common operations you will be able to perform:

// creating a person
var person = Person()
person.name = "Stef"
person.birth = LocalDate.of(1910, Month.FEBRUARY, 1)
person.status = Status.Alive

// persist it: if you keep the default ObjectId ID field, it will be populated by the MongoDB driver
personRepository.persist(person)

person.status = Status.Dead;

// Your must call update() in order to send your entity modifications to MongoDB
personRepository.update(person);


// delete it
personRepository.delete(person);

// getting a list of all Person entities
val allPersons = personRepository.listAll()

// finding a specific person by ID
// here we build a new ObjectId, but you can also retrieve it from the existing entity after being persisted
ObjectId personId = new ObjectId(idAsString);
person = personRepository.findById(personId) ?: throw Exception("No person with that ID")

// finding all living persons
val livingPersons = personRepository.list("status", Status.Alive)

// counting all persons
val countAll = personRepository.count()

// counting all living persons
val countAlive = personRepository.count("status", Status.Alive)

// delete all living persons
personRepository.delete("status", Status.Alive)

// delete all persons
personRepository.deleteAll()

// delete by id
val deleted = personRepository.deleteById(personId)

// set the name of all living persons to 'Mortal'
var updated = personRepository.update("name", "Mortal").where("status", Status.Alive)

All list methods have equivalent stream versions.

val persons = personRepository.streamAll();
val namesButEmmanuels = persons
    .map { it.name.toLowerCase() }
    .filter { it != "emmanuel" }

For more examples, please consult the Java version for complete details. Both APIs are the same and work identically except for some Kotlin-specific tweaks to make things feel more natural to Kotlin developers. These tweaks include things like better use of nullability and the lack of Optional on API methods.

Setting up and configuring MongoDB with Panache

To get started using MongoDB with Panache with Kotlin, you can, generally, follow the steps laid out in the Java tutorial. The biggest change to configuring your project is the Quarkus artifact to include. You can, of course, keep the Java version if you need but if all you need are the Kotlin APIs then include the following dependency instead:

pom.xml

<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-mongodb-panache-kotlin</artifactId>  (1)
</dependency>

1	Note the addition of `-kotlin` on the end. Generally you’ll only need this version but if your project will be using both Java and Kotlin code, you can safely include both artifacts.

build.gradle

implementation("io.quarkus:quarkus-mongodb-panache-kotlin") (1)

1	Note the addition of `-kotlin` on the end. Generally you’ll only need this version but if your project will be using both Java and Kotlin code, you can safely include both artifacts.

First: an example
Using the repository pattern
Setting up and configuring MongoDB with Panache