Services

• Data model
• Persistance
• External requests
• (...)

Controllers

• Receive requests from client
• Define endpoints & methods
• Use services

Modules

• Group code (by functionality, for example)
• At least one root module
  (AppModule)

More pieces

Pipes

e.g. for request validation

Exceptions

for error handling

Guards

for authorization

Interceptors

for manipulating requests and responses

TypeORM

• Decorators everywhere
• Works with MySQL, Postgres, Oracle...