Hello async my old friend

Let me present you vertx-jooq-async: the world’s first fully async and type-safe SQL code generation and execution tool for VertX™. Async? Wasn’t it asynchronous before? It was, but what the code did was wrapping JDBC-calls using Vertx’ executeBlocking-method, which just shifts the blocking code from one event loop to another (see also).

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With this release however, things have changed. jOOQ is still used for generating code and creating type-safe queries, but code is executed utilizing vertx-mysql-postgresql-client. That library in turn is based on a non-blocking driver for MySQL and Postgres databases, so this time it is really non-blocking.

Although some stuff is yet missing – you should go and check out the github-page. Now.

The Future Is Here

Getting asynchronous operations right is hard. And when you have to pass a result of one function to the next, it can only get worse. Since today, vertx-jooq’s API for instance only allowed asynchronous operations with a callback handler, which leads to code fragments like this:

What annoys me about this is that I have to define in each handler if it succeeded and what to do if an exception occurred on the database layer. Especially when you have to nest three or more operations this looks ugly. Of course this problem is not new and there exists an alternative approach which is using and composing Java 8 java.util.concurrent.CompletableFuture. By doing so, the same code becomes easier and more readable:

But using CompletableFuture within the Vertx world leads to a problem: Vertx has it’s own threading model to achieve the performance it actually has. On the other hand, some methods of CompletableFuture, e.g. CompletableFuture.supplyAsync(Supplier), run tasks on the common ForkJoinPool which would break the Vertx contract. Open-source-software to the rescue, there is a solution to this problem: VertxCompletableFuture. This special implementation guarantees that async operations run on a Vertx context unless you explicitly specify an Executor in one of the overloaded xyzAsync-methods*.

And here comes even better news: starting from version 2, vertx-jooq also supports this way of dealing with asynchronous database operations by utilizing VertxCompletableFuture. Checkout the new vertx-jooq-future module and the according code generator to create your CompletableFuture-based DAOs.

* There have been discussions in the Vertx developer group about a CompletableFuture based API, e.g. here and especially here. The current status is that they do not provide such API officially, mostly because VertxCompletableFuture breaks the contract of the supplyAsync-methods, since it runs within the Vertx context and not the ForkJoinPool. Also when you pass this CompletableFuture subclass to code that expects a regular CompletableFuture, it breaks the Liskov substitution principle and OOP (thanks for pointing that out in the comments Julien). My opinion is, that if you are using Vertx you are aware of the special threading model and can tolerate that behavior. But, of course, it’s up to you.

Vertx loves jOOQ

I’ve recently published a library that connects two frameworks I used a lot in the past: Vertx and jOOQ. Vertx is a “reactive tool-kit for the JVM” that enables you to write non-blocking code and has some nice features built in, like webserver/socketserver-implementation, a message-bus that can run on one or more instances in one network and many more goodies you should check out. On the other hand, if you are coding in Java and you like SQL, there is no way around jOOQ. In my opinion, jOOQ’s two killerfeatures are the possibility to write typesafe SQL and the awesome code-generator that generates POJOs, DAOs and Table-implementations based on your database schema (schema first!). However jOOQ is using JDBC under the hood which blocks the calling thread until the database operation completes.

That is where my library hooks in: it provides a code-generator that adds non-blocking CRUD-methods to all generated DAOs and converter methods that allow you to convert from Vertx’ JsonObject into jOOQ’s POJOs and vice versa.

For code examples, please refer to the github-page.