Hello again, friends! 👋 Did you enjoy our first part about Domain-Driven Design (DDD)? If you missed it, you can read it here. Today, we’re going to learn more about DDD using a fun pizza shop story.
In this part, ‘DDD Building Blocks: A Pizza Shop Story’, we’ll learn about important DDD concepts like Ubiquitous Language, Bounded Context, Entities, and more.
Ready to make some pizza and learn about DDD? Let’s go! 🎉
Understanding DDD Basics
Problem Domain
The specific problem the software you’re working on is trying to solve.
The Pizza Puzzle 🧩
Think of the Problem Domain as the specific issue our pizza shop is trying to solve. In our case, the problem domain might be: “How can we efficiently manage orders and create delicious pizzas that satisfy our customers?”
Core Domain
The key differentiator for the customer’s business — something they must do well and cannot outsource.
Our Pizza Secret 🍕
Our Core Domain is the unique aspect that sets our pizza shop apart from others. It’s something we must excel at and can’t outsource. For instance, it could be our secret pizza sauce recipe that keeps customers coming back for more!
Subdomains
Separate applications or features your software must support or interact with.
The Supporting Roles 🍽️
Subdomains are like the additional features or tasks our pizza shop must handle alongside making pizzas. This could include managing inventory, handling deliveries, or maintaining customer loyalty programs.
Ubiquitous Language
The language uses terms from a domain model that programmers and domain experts use to discuss that particular sub-system.
Our Pizza Words 🔐
Imagine running a pizza place where everyone uses special pizza words. This shared language, in DDD, is our Ubiquitous Language. It’s our secret handshake-making sure everyone on the team knows about our pizza work.
Bounded Context
A specific responsibility, with explicit boundaries that separate it from other parts of the system.
The Pizza Shop Wall 🏢
The Bounded Context works like the shop’s walls. Inside these walls, “cheese” means a yummy pizza topping. Outside, it could mean anything else! This helps us understand where our pizza ideas work and where they don’t.
Context Mapping
The process of identifying bounded contexts and their relationships to one another.
The Pizza Process Map 🗺️
Context Mapping is like creating a map of our pizza shop’s various processes and how they relate to each other. It helps us visualize the Bounded Contexts and how they interact.
Shared Kernel
Part of the model is shared by two or more teams, who agree not to change it without collaboration.
The Common Pizza Base 🍕✨
The Shared Kernel is a part of our pizza shop model that’s shared between different teams. For instance, both our pizza-making team and our delivery team might use the same customer database. They agree not to change it without collaborating, ensuring a consistent customer experience.
Bounded Context: The Pizza Shop Wall 🏢
The Bounded Context works like the shop’s walls. Inside these walls, “cheese” means a yummy pizza topping. Outside, it could mean anything else! This helps us understand where our pizza ideas work and where they don’t.
Exploring DDD Building Blocks
Entities and Value Objects: Pizzas vs Ingredients 🍕🧀
Entities are like pizzas – each one is unique.
public class Pizza {
private Long id;
private String name;
// ... other ingredients, methods
}Value Objects, however, are like the ingredients we use. They’re important but don’t have a unique identity.
public class Ingredient {
private String taste;
private String texture;
// ... other attributes, methods
}Aggregates: The Pizza Combo 🍕➕🧀
Aggregates are a combination of entities and value objects that form a single unit. For example, a Margherita pizza is an aggregate of the Pizza entity and the Ingredient value object.
public class MargheritaPizza {
private Pizza base;
private List<Ingredient> ingredients;
// ... other attributes, methods
}Domain Events: The Pizza Order Alert 📣
When a customer orders a pizza, it’s a Domain Event. It’s a signal that a pizza needs to be made, without worrying about the who and why of the order.
public class PizzaOrderedEvent {
private String pizzaType;
private Date orderTime;
// ... other attributes, methods
}DDD in Action: Questions and Answers
Let’s test your understanding with a DDD Challenge! 🎲
1. What’s the secret handshake that our pizza shop team uses?
2. What is the ‘wall’ that helps our pizza ideas make sense?
3. Who are the pizzas and their ingredients in our pizza story?
4. What term do we use for the pizza and its ingredients together?
5. Who tells everyone when a pizza needs to be made?
Think about it! Ready to check your answers? Let’s move to the answer section.
Solving the DDD Puzzle: Answers 🍕🎲
Let’s see how you did!
1. The secret handshake is the Ubiquitous Language.
2. The ‘wall’ is called the Bounded Context.
3. In our story, pizzas are Entities and their ingredients are Value Objects.
4. When the pizza and its ingredients come together, we call it an Aggregate.
5. The alert is a Domain Event.
Conclusion
That’s it, folks! I hope this pizza-themed story helped you understand the basics of Domain-Driven Design. Remember, DDD is like a recipe—with the right parts (Entities, Value Objects, Aggregates) and the right process (Ubiquitous Language, Bounded Context, Domain Events), you’re ready to make some amazing software.
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Keep coding and learning! 🚀👨💻
