How Can I Model the Database Using Entities?

[ghost]

I'm trying to figure out how to model my database using entities. For instance, I want to model a 'products' table through a 'Product' entity. How would I go about doing this?

Is it necessary to create the database first before I start coding?

I would really appreciate some guidance on this matter. I'm planning to use this template for projects, but I need to solve this "problem" first.

Thank you!

[Sairyss]

Depends on what size and complexity the project is. If your project is relatively small and simple (CRUD application), I wouldn't recommend using this template and creating DDD entities, it's simply not needed.

If you are building a large project with a complex business logic, here are some recommendations:

1. Define what your application can do. For example, if it is an online shop, you may need some entities: Customers, Products, Orders, etc.
2. Then go lower and decide how those entities will interact with each other. Customers can place Orders to buy Products, for example, when an order is placed it can emit an event that triggers a notification to a shipping department, and so on. You can use event storming to plan this.
3. Then decide what each entity can do by itself. Lets say, a Product must represent a real world item, with a name, description, price, etc. and must provide certain functionality, for example you can change product description or apply product specific discount. In DDD it can be represented as a class (domain entity) with properties and methods:

class ProductEntity {
  price: number;
  name: string;
  description: string;
  
   changeDescription(description: string) {
     // ...
   }

   applyDiscount(discount:number) {
    // ...
   }

4. After you defined your domain entities, you can decide how to better represent them in the database. For example if your entities have relations, relational model databases (SQL) are an appropriate choice. Create tables that represent how you want to store your entities. Some entities (like Product) can have same database columns as properties of your domain entity, but more complex entities may have things like Value Objects or sub-entities inside, so you will need to decide how to store them. For example, in this project UserEntity has an Address, which is a value object. But in the database it is represented as userSchema where address is flattened out (using toPersistence method in the mapper), because it's easier to store it like that. You just create a database schema and map your entity to your database representation using a mapper.

Keep in mind that Domain Entities represent the domain business logic, and must be modeled to accommodate the domain.
On the other hand, database tables just define how you store your data and to accommodate queries.

How to model entities and tables totally depends on the project and requires some experience, so keep practicing and it will come eventually.