Promoting open/close principle and loose coupling between components



When to check when business rules apply?

The question is quite common in software development. Given an instance of a class, you want to know when to check if a class is valid or not. Do you skip validations before executing an action or do you first check if the instance is valid before executing an action?

Let’s see a simple example. Image an entity called FlightReservation and some validation or better business invariant rules that require a flight reservation to be valid when it contains no more than max_passenger passengers.

class FlightReservation < AggregateRoot
MaxPassengersReachedError =
attr_reader :passengers
attr_reader :max_passengers
def initialize(max_passenger)…

Reduce coupling and dependencies between communicating objects. An event-driven approach.

Design patterns are reusable solutions to a commonly occurring problem within a given context in software design [1]. Having design patterns in mind is a good habit in general, but it should be avoided to apply them from the beginning. Thinking about good design is a good thing but applying it all the time can hurt your software, maintenance and the effort that someone needs to put in order to understand what a single class does. …


A repository performs the tasks of an intermediary between the domain model layers and data mapping, acting in a similar way to a set of domain objects in memory. Client objects declaratively build queries and send them to the repositories for answers. Conceptually, a repository encapsulates a set of objects stored in the database and operations that can be performed on them, providing a way that is closer to the persistence layer. …


Recently I came across a codebase where we had to add a new feature on top of an existing implementation. It was implemented a couple of months ago and still, it kept growing an growing. …

Laerti Papa

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