# Minitalk ## Web Application Architecture ### 07/02/2020 [`@pereirazc`](https://github.com/pereirazc/buckpal) --- #### Many layers of bad practices  --- #### Database-driven development Why are we making the **database** the foundation of our architecture and not the **domain logic**? --- #### Basic  --- #### Layer shortcuts  --- #### Fat Services  --- ## Let's clean it up :shower:  **Alistair Cockburn**  **Robert Martin aka "Uncle Bob"** --- ## Let's clean it up :shower:  by Robert C. Martin --- ### Hexagonal Architecture  --- ### Clean Architecture  --- ### Reponsabilities of the Controller Adapter * Map HTTP request to objects * Perform **authorization** checks * Validate input * **Map input to the input model of the use case** * **Call the use case** * Map output of the use case back to HTTP * Return HTTP response --- ### Responsabilities of an Use Case * Take input * **Validate business rules** * Manipulate model state * Return output --- ### Responsabilities of Persistence/DB Adapter * Take input * **Map input into database format** * Send input to the database * Map database output into application format * Return output --- ## Hands On  --- #### Hands On - Transfer money :money_with_wings:  --- #### Architectural Overview  The web controller calls an incoming port, which is implemented by a service. The service calls an outgoing port, which is implemented by an adapter. --- #### *SendMoney* Use Case  A service implements a use case, modifies the domain model and calls an outgoing port to persist the modified state. --- #### AccountController ```java public class AccountController { private final SendMoneyUseCase sendMoneyUseCase; ... @PostMapping(path = "/accounts/sendMoney/{sourceAccountId}/{targetAccountId}/{amou\ nt}") void sendMoney( @PathVariable("sourceAccountId") Long sourceAccountId, @PathVariable("targetAccountId") Long targetAccountId, @PathVariable("amount") Long amount) { SendMoneyCommand command = new SendMoneyCommand( new AccountId(sourceAccountId), new AccountId(targetAccountId), Money.of(amount)); sendMoneyUseCase.sendMoney(command); ... } ... } ``` --- #### SendMoneyCommand ```java public class SendMoneyCommand { private final AccountId sourceAccountId; private final AccountId targetAccountId; private final Money money; public SendMoneyCommand(...) ``` --- #### Account ```java public class Account { private AccountId id; private Money baselineBalance; private ActivityWindow activityWindow; public Money calculateBalance() ... public boolean withdraw(Money money, AccountId targetAccountId) ... public boolean deposit(Money money, AccountId sourceAccountId) ... } ``` --- #### SendMoneyService ```java public class SendMoneyService implements SendMoneyUseCase { private final LoadAccountPort loadAccountPort; private final AccountLock accountLock; private final UpdateAccountStatePort updateAccountStatePort; public boolean sendMoney(SendMoneyCommand command) { // validate business rules // manipulate model state // return output } } ``` --- #### Account Repository vs. Exclusive Ports **OK**  Centralizing all database operations into a single outgoing port interface makes all services depend on methods they don’t need. --- #### Account Repository vs. Exclusive Ports **BETTER**  Applying the Interface Segregation Principle removes unnecessary dependencies and makes the existing dependencies more visible