In this example, a user module is implemented according to Nest.js philosophy. There are a few core elements: module, controller, service, entity, dtos, decorator, interceptor.
A Module class sets providers that are used from within the current module, imported and exported modules.
A Controller contains route handlers for retrieving user by id and for user updating.
A Service is a provider of functions (signIn, signUp, getUser, and updateUser). It's used as a dependency in the controller and other providers.
An Entity is a TypeORM object that represents the user data (many-to-many relationship is used).
Two DTOs (Data Transfer Object) are objects that define how the data will be sent over the network in case of the user creating and updating (used for validation).
Custom Decorator is used for additional validation on email existence.
An Interceptor is used for manipulating with a request before validation.
Inheritance, encapsulation, dependency injections, decorators, typing are used in this code example.