From the answer to Must the use cases extend the entities in Clean Architecture? I have known that the use cases must NOT extend the entities. It's fine, but what do I have to do with the properties of entities which are depending on the application?
Very strictly speaking, these rules (note: the enterprise business rules) would make or save the business money, irrespective of whether they were implemented on a computer. They would make or save money even if they were executed manually.
The below entity is matching with this concept because each product has a title which could be written on the physical label and price:
class Product { public title: string; public price__dollars__withoutTax: number; public constructor(properties: Readonly<{ title: string; price__dollars__withoutTax: number; }>) { this.title = properties.title; this.price__dollars__withoutTax = properties.price__dollars__withoutTax; } } Unlike this, the below class has some fields which exist only inside the application - ID, createdAt__ISO86101, updatedAt__ISO86101
class Product { public readonly ID: number = Product.generateID(); public title: string; public price__dollars__withoutTax: number; public createdAt__ISO86101: string; public updatedAt__ISO86101?: string; public constructor(properties: Readonly<{ title: string; price__dollars__withoutTax: number; }>) { this.title = properties.title; this.price__dollars__withoutTax = properties.price__dollars__withoutTax; this.createdAt__ISO86101 = new Date().toISOString(); } private static counterForID_Generating = -1; private static generateID(): number { Product.counterForID_Generating++; return Product.counterForID_Generating; } } How the second version of Product class should be organized in the Clean Architecture hierarchy?
createdAt__ISO86101andupdatedAt__ISO86101are application specific? IfProductas an entity of the domain is soabstract, then let it be so. Don't make it concrete. It can be just an "abstraction" too. By the way, there're other techniques to expand data models. One of them can be persisting additional data in different places. Another is via decorators and composition. Remember that the domain will not care how data is persisted or managed "out" of its scope.createdAt__ISO86101is not the date/time of the production of physical product - it just the date of adding to digital database. TheupdatedAt__ISO86101is the date/time of updating the data in digital database. "By the way, there're other techniques to expand data models." - thank you for the advise. Sounds great, but have you some links with examples?