Getting started with Quarkus, reactive MySQL datasource, & Kotlin

[jehrenzweig-leagueapps]

I'm pretty new to Quarkus, reactive programming, & Kotlin, and I'm having trouble figuring out how to get my first reactive SQL query working. Here's the repository class I have right now, which I've written using the "Reactive SQL Clients" page's "Prepared Queries" info:

import io.vertx.mutiny.mysqlclient.MySQLPool
import io.vertx.mutiny.sqlclient.Row
import io.vertx.mutiny.sqlclient.RowSet
import io.vertx.mutiny.sqlclient.Tuple

@ApplicationScoped
class PotatoTypeJdbcReadRepository(
	@ReactiveDataSource("test") private val testDataSource: MySQLPool
) : IPotatoTypeReadRepository {
	override suspend fun getPotatoTypeByName(name: String): PotatoTypeEntity? {
		// Return a specific potato type that matches the specified name.
		val something = this.testDataSource
			.preparedQuery("select * from PotatoTypes where NAME = ? order by NAME")
			.execute(Tuple.of(name))
			.onItem().transform(RowSet::iterator) 
			.onItem().transform(iterator -> iterator.hasNext() ? from(iterator.next()) : null)

		// Placeholder; the SQL result is what I want to return
		return PotatoTypeEntity()
	}
}

---

[UPDATE @ 2022-06-17]
I've created a repository with a sample application to help demonstrate this behavior:

• https://github.com/jehrenzweig-leagueapps/quarkus-reactive-programming-20220617

The PotatoTypeReadOnlyRepository class' getPotatoTypeByName() method successfully submits a SQL query & returns a PotatoType object, which is then returned as the API response body.

However, if I call the PotatoTypeReadOnlyRepository class' getPotatoTypeByNameReactive()
method, the API endpoint that calls it returns a HTTP 500 response, because I'm doing one or more things wrong.

The problem here is that I can't figure out to write the reactive equivalent of my non-reactive repository method. Any help or pointers would be greatly appreciated!

[quarkus-bot[bot]]

/cc @evanchooly

[evanchooly]

I'm spitballing here as I don't have a place to test this syntax out but what if you passed RowSet<PotatoTypes>::iterator? I'm otherwise not terribly familiar with the reactive APIs.

[jehrenzweig-leagueapps]

@evanchooly I'm pretty sure I already tried that, and it didn't change the exception message in any way. I've already commented out all of my reactive code for now, so I can't immediately check to be sure.

FWIW I figured creating a repository with example code would be more helpful in facilitating this discussion. But I also thought I'd post before that repo was ready, on the off-chance somebody with a lot of Kotlin experience immediately knew what the answer was. I'll get a sample repo ready tomorrow & post a link here.

[gsmet]

@jehrenzweig-leagueapps not sure exactly what you're trying to achieve but just so you know you can use Quarkus without reactive programming if you're more familiar with it. Reactive programming is a possibility but you can do everything imperative if you prefer.

[jehrenzweig-leagueapps]

@gsmet Yeah, I have database calls working without using io.quarkus:quarkus-reactive-mysql-client to interact with my MySQL database using a reactive datasource. I may have to go with that for the time being, since reactive programming is so different & I'm having trouble figuring out how to achieve the same results I already get using an imperative approach. Thought I'd give it a try, though.

@evanchooly I had a bit more time than I'd expected today, so I gave the reactive method another try and got it to compile. Here's what it looks like now:

val uniPotatoTypeEntity: Uni<PotatoTypeEntity?> = this.testReactiveDataSource
	.preparedQuery("select * from PotatoTypes where NAME = ? order by NAME")
	.execute(io.vertx.mutiny.sqlclient.Tuple.of(name))
	.onItem().transform(io.vertx.mutiny.sqlclient.RowSet<io.vertx.mutiny.sqlclient.Row>::iterator)
	.onItem().transform { iterator ->
		if (iterator.hasNext()) {
			PotatoTypeEntityMapper().getPotatoTypeEntity(iterator.next())
		} else {
			null
		}
	}

What I didn't originally understand in the official docs was that the from() method was not a built-in Kotlin or Mutiny method, but a custom method that mapped the RowSet to a POJO class instance. Once I replaced from() with my own PotatoTypeEntityMapper().getPotatoTypeEntity() method, it works.

Now I'm stuck on something completely new & different: how to extract the PotatoTypeEntity? object from my Uni<PotatoTypeEntity?> object.

[jehrenzweig-leagueapps]

I just updated my original post with a link to a GitHub repository containing a sample application:

• https://github.com/jehrenzweig-leagueapps/quarkus-reactive-programming-20220617

It uses Quarkus DevServices & Flyway to create two new databases, for the life of the running application. One DB is exposed using a non-reactive datasource, the other using a reactive datasource. The non-reactive repository method works properly, but the reactive repository method equivalent is broken -- I'm doing one or more things wrong.