Prisma CQS

Simple abstractions we use to follow the CQS Principle in applications.

Motivation

The CQS Principle states that "every method should either be a command that performs an action, or a query that returns data to the caller, but not both" to reduce side effects.

In our projects we use abstractions like Query & QueryHandler as well as Command & CommandHandler to follow this principle. However, there is a bit of fine print here that makes it worthwhile to reuse this in the form of a library:

• a command / query needs to be valid (determined by a MessageValidator), otherwise a Command/Query-ValidationExcption will be thrown
• a command / query needs to be valid (determined by an optional message on the handler), otherwise a Command/Query-ValidationException will be thrown
• a command / query needs to be verified by a mandatory method in the handler, otherwise a Command/Query-VerificationException will be thrown
• when a command / query is handled, any exception it may throw is wrapped in a Command/Query-HandlingException

Usage

TODO

Maven

cqs is a parent-only artifact (packaging: pom).

Use cqs-core as dependency:

    <dependency>
      <groupId>eu.prismacapacity</groupId>
      <artifactId>cqs-core</artifactId>
      <version><!-- put the desired version in here--></version>
    </dependency>

Configuration

TODO

Example

TODO

Configure a retry behaviour for Command and Query handlers

TODO

Migration

TODO