Скачать или смотреть Understanding Reactive Programming with Spring Boot: Troubleshooting R2DBC Test Issues

Learn how to effectively work with reactive databases in Spring Boot and troubleshoot common testing issues with `R2DBC`.
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Introduction to Reactive Database Testing with Spring Boot

As software development embraces more modern methodologies, reactive programming has gained significant attention, especially in the Spring Boot community. However, for beginners, it can be challenging to grasp the various intricacies that come with this programming style. In this post, I'll work through a common issue one might encounter when conducting tests using Spring Boot’s R2DBC for reactive database operations.

The Problem: Behavioral Expectations vs Reality

Imagine you're working on a Spring Boot application that saves data to a MariaDB database. You create a repository to manage your database interactions with minimal settings and expect everything to work seamlessly. However, when running a test to save a record, you find that the methods intended to log the success of this operation are not being called. Instead, you only see a confirmation message that indicates execution reached a certain point in your code—a frustrating situation for anyone trying to learn.

The Setup: Code Overview

To provide context, let’s examine the simplified environment in which this issue arises. Below is the structure of the key components:

Database Setup

First, the MariaDB schema for our application is defined as follows:

[[See Video to Reveal this Text or Code Snippet]]

Data Representation

Next, we have our DataDAO class, which represents the records in the persons table:

[[See Video to Reveal this Text or Code Snippet]]

Repository Interface

An interface for data access is set up using ReactiveCrudRepository:

[[See Video to Reveal this Text or Code Snippet]]

Test Class

The test class that simulates saving a record is structured as follows:

[[See Video to Reveal this Text or Code Snippet]]

The Misunderstanding: What Went Wrong?

At first glance, it seems straightforward—create a Mono for the saved data, add some logging functionality, and invoke block() to wait for the operation to complete. However, the crux of the issue lies in how a Mono behaves.

When you invoke a method that returns a Mono, like save(), you get a new instance of Mono. Consequently, when you attempt to call methods like doOnNext() or doOnSuccess() on it, you're essentially manipulating a different Mono object than the one returned to you originally and intended for blocking.

Correcting the Approach: How to Fix It

To achieve the intended behavior, you need to chain the method calls together directly on the Mono returned from the repository's save() method. Here’s how you can structure it correctly:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By re-arranging your code to call the side-effect methods directly on the row from theRepo.save(), you ensure that you are working with the latest instance of the Mono. This adjustment will allow your logging statements to execute as expected, confirming that the data has been saved successfully.

If you’re new to reactive programming, such pitfalls are common, and understanding the nuances of how reactive types behave is crucial for overcoming them. Embrace the learning curve and continually refine your understanding of frameworks like Spring Boot and reactive programming.

Hopefully, this breakdown helps clarify the mishap and aids any other developers who might stumble upon a similar issue. Happy coding!