Typical Shopping Cart

This article is about a shopping cart on a typical online shop.

Let’s imagine it

We’ll have to save identification of the product and the amount, it’s easy.

Don’t repeat yourself

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system

— Andy Hunt and Dave Thomas, The Pragmatic Programmer

Car in API

We develop multiple systems that communicate via API in JSON format. The most transferred information are information about cars.

An example of such transferred car

{…

We use access modifiers to hide certain properties or methods — public, protected, private. Final is used to disallow children. But why would we hide something or disallow anything? Why to do such things?

We have to often implement new features or modify existing ones. This results in extending current…

How to apply

1. Hear the story
2. Understand terms
3. Extract scenarios
4. Select use cases
5. Model concepts
6. Write tests + code
7. Connect to the infrastructure

1. Hear the story

The first and most important step of programming. A person who knows the domain, the topic we are going to program, has to…

Let’s think for a while — where do we use class/interface name?

• During creating object from the class (new Product(...))
• In usage

Creating objects

We aren’t able to create objects from abstract classes and interfaces, so it is always without prefix/suffix. I hope no one suggest to call a concrete class a…

Domain-driven design is about the domain. Domain services and domain factories do not exist in the domain. In general we shouldn’t use them.

They are artificial constructions and this causes a lot of problems with code understanding, maintainability and also divergence between the domain, the model and the code.

Domain Service

We…

Product Name Story

We worked on an e-shop and the product had exactly one name. One day we faced confronted with the reality — the e-shop has to be multilingual. I imagined a new database table for every language field immediately, and I was disgusted by all the tables that had to be…

The repository is a persistent collection that we know from repository article. We expect that we know the cart model from model and implementation articles. But it doesn’t make any harm if we repeat the cart model again.