Day 26 task

README.MD

@@ -36,4 +36,5 @@ Every task will focus on Java, popular libraries and frameworks. So, let's start
 * [Day 22](/day022/README.MD)
 * [Day 23](/day023/README.MD)
 * [Day 24](/day024/README.MD)
-* [Day 25](/day025/README.MD)
+* [Day 25](/day025/README.MD)
+* [Day 26](/day026/README.MD)

day026/README.MD

@@ -0,0 +1,8 @@
+# Day 26 - transactional outbox
+
+Today's task is to implement a pattern that sends out events and persist aggregate changes in single transaction.
+Usually it is implemented on database with a table dedicated for events, where they are stored. 
+Events are picked up from this table and sent by another thread.
+
+The most important for this pattern to work is to persist changes and events in the same transaction.
+For task clearness purposes, tests for transaction checks are skipped, but feel free to write them.

day026/build.gradle

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+plugins {
+    id 'org.springframework.boot' version '3.0.1'
+    id 'io.spring.dependency-management' version '1.1.0'
+    id 'java'
+}
+
+group 'com.pawelpluta'
+version '0.0.1'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    runtimeOnly 'org.postgresql:postgresql'
+    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
+    testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    testImplementation 'org.testcontainers:testcontainers:1.17.6'
+    testImplementation 'org.testcontainers:postgresql:1.17.6'
+    testImplementation 'com.fasterxml.jackson.core:jackson-databind:2.13.3'
+    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.9.1'
+    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.9.1'
+}
+
+test {
+    useJUnitPlatform()
+}
+
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(19))
+    }
+}

day026/settings.gradle

@@ -0,0 +1 @@
+rootProject.name = 'day024'

day026/src/main/java/com/pawelpluta/day026/BankAccount.java

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+package com.pawelpluta.day026;
+
+import java.math.BigDecimal;
+import java.util.Collections;
+import java.util.List;
+import java.util.UUID;
+
+public class BankAccount {
+
+    private final String accountNumber;
+    private final BigDecimal balance;
+    private final List<Event> events;
+
+    private BankAccount(String accountNumber, BigDecimal balance, List<Event> events) {
+        this.accountNumber = accountNumber;
+        this.balance = balance;
+        this.events = events;
+    }
+
+    public String accountNumber() {
+        return accountNumber;
+    }
+
+    public BigDecimal balance() {
+        return balance;
+    }
+
+    public List<Event> events() {
+        return events;
+    }
+
+    public static BankAccount of(String accountNumber, BigDecimal balance) {
+        return new BankAccount(accountNumber, balance, Collections.emptyList());
+    }
+    BankAccount handle(ChargeAccountCommand command) {
+        if (balance.compareTo(command.amount()) >= 0) {
+            BigDecimal updatedBalance = balance.subtract(command.amount());
+            return new BankAccount(
+                    accountNumber,
+                    updatedBalance,
+                    List.of(new BankAccountBalanceDecreased(accountNumber, balance, updatedBalance)));
+        } else {
+            return new BankAccount(
+                    accountNumber,
+                    balance,
+                    List.of(new AccountChargeRejectedDueToInsufficientFounds(accountNumber, balance, command.amount())));
+        }
+    }
+
+    static class BankAccountBalanceDecreased implements Event {
+
+        private final String id;
+        private final String accountNumber;
+        private final BigDecimal oldBalance;
+        private final BigDecimal newBalance;
+
+        BankAccountBalanceDecreased(String accountNumber, BigDecimal oldBalance, BigDecimal newBalance) {
+            id = UUID.randomUUID().toString();
+            this.accountNumber = accountNumber;
+            this.oldBalance = oldBalance;
+            this.newBalance = newBalance;
+        }
+
+        @Override
+        public String id() {
+            return id;
+        }
+
+        @Override
+        public String jsonBody() {
+            return "{}";
+        }
+    }
+
+    static class AccountChargeRejectedDueToInsufficientFounds implements Event {
+
+        private final String id;
+        private final String accountNumber;
+        private final BigDecimal balance;
+        private final BigDecimal charge;
+
+        AccountChargeRejectedDueToInsufficientFounds(String accountNumber, BigDecimal balance, BigDecimal charge) {
+            id = UUID.randomUUID().toString();
+            this.accountNumber = accountNumber;
+            this.balance = balance;
+            this.charge = charge;
+        }
+
+        @Override
+        public String id() {
+            return id;
+        }
+
+        @Override
+        public String jsonBody() {
+            return "{}";
+        }
+    }
+}

day026/src/main/java/com/pawelpluta/day026/BankAccountRepository.java

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+package com.pawelpluta.day026;
+
+import java.util.Optional;
+
+public interface BankAccountRepository {
+    Optional<BankAccount> findById(String id);
+    void save(BankAccount account);
+}

day026/src/main/java/com/pawelpluta/day026/ChargeAccountCommand.java

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+package com.pawelpluta.day026;
+
+import java.math.BigDecimal;
+
+record ChargeAccountCommand(String accountId, BigDecimal amount) {
+}

day026/src/main/java/com/pawelpluta/day026/CommandHandler.java

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+package com.pawelpluta.day026;
+
+import org.springframework.stereotype.Service;
+
+@Service
+class CommandHandler {
+
+    private final BankAccountRepository accountRepository;
+
+    CommandHandler(BankAccountRepository accountRepository) {
+        this.accountRepository = accountRepository;
+    }
+
+    void handle(ChargeAccountCommand command) {
+        accountRepository.findById(command.accountId())
+                .ifPresent(bankAccount -> accountRepository.save(bankAccount.handle(command)));
+    }
+}

day026/src/main/java/com/pawelpluta/day026/Event.java

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+package com.pawelpluta.day026;
+
+public interface Event {
+    String id();
+    String jsonBody();
+
+    record EventVO(String id, String jsonBody) implements Event {}
+}

day026/src/main/java/com/pawelpluta/day026/EventSupplier.java

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+package com.pawelpluta.day026;
+
+import java.util.List;
+
+public interface EventSupplier {
+    List<Event> fetchEventsToSend();
+}

day026/src/main/java/com/pawelpluta/day026/TransactionalOutboxApp.java

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+package com.pawelpluta.day026;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+class TransactionalOutboxApp {
+
+    public static void main(String[] args) {
+        SpringApplication.run(TransactionalOutboxApp.class, args);
+    }
+}

day026/src/main/java/com/pawelpluta/day026/jpa/BankAccountEntity.java

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+package com.pawelpluta.day026.jpa;
+
+import com.pawelpluta.day026.BankAccount;
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+
+import java.math.BigDecimal;
+
+@Entity
+@Table(name = "accounts")
+class BankAccountEntity {
+    @Id
+    @Column(name = "account_id")
+    private String id;
+    @Column(name = "balance")
+    private BigDecimal balance;
+
+    public BankAccountEntity() {
+    }
+
+    public BankAccountEntity(String id, BigDecimal balance) {
+        this.id = id;
+        this.balance = balance;
+    }
+
+    static BankAccountEntity from(BankAccount account) {
+        return new BankAccountEntity(
+                account.accountNumber(),
+                account.balance());
+    }
+
+    BankAccount toModel() {
+        return BankAccount.of(id, balance);
+    }
+}

day026/src/main/java/com/pawelpluta/day026/jpa/EventEntity.java

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+package com.pawelpluta.day026.jpa;
+
+import com.pawelpluta.day026.Event;
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+
+@Entity
+@Table(name = "events_outbox")
+class EventEntity {
+    @Id
+    @Column(name = "event_id")
+    private String id;
+    @Column(name = "body")
+    private String body;
+    @Column(name = "sent")
+    private Boolean sent;
+
+    public EventEntity() {
+    }
+
+    public EventEntity(String id, String body) {
+        this.id = id;
+        this.body = body;
+        sent = false;
+    }
+
+    static EventEntity from(Event event) {
+        return new EventEntity(
+                event.id(),
+                event.jsonBody());
+    }
+
+    String getId() {
+        return id;
+    }
+
+    String getBody() {
+        return body;
+    }
+}

day026/src/main/java/com/pawelpluta/day026/jpa/JpaBankAccountEntityRepository.java

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+package com.pawelpluta.day026.jpa;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+interface JpaBankAccountEntityRepository extends JpaRepository<BankAccountEntity, String> {
+}

day026/src/main/java/com/pawelpluta/day026/jpa/JpaBankAccountRepository.java

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+package com.pawelpluta.day026.jpa;
+
+import com.pawelpluta.day026.BankAccount;
+import com.pawelpluta.day026.BankAccountRepository;
+import org.springframework.stereotype.Repository;
+
+import java.util.Optional;
+
+@Repository
+class JpaBankAccountRepository implements BankAccountRepository {
+
+    private final JpaBankAccountEntityRepository repository;
+
+    JpaBankAccountRepository(JpaBankAccountEntityRepository repository) {
+        this.repository = repository;
+    }
+
+    @Override
+    public Optional<BankAccount> findById(String id) {
+        return repository.findById(id).map(BankAccountEntity::toModel);
+    }
+
+    @Override
+    public void save(BankAccount account) {
+        repository.save(BankAccountEntity.from(account));
+    }
+}

day026/src/main/java/com/pawelpluta/day026/jpa/JpaEventEntityRepository.java

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+package com.pawelpluta.day026.jpa;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+
+@Repository
+interface JpaEventEntityRepository extends JpaRepository<EventEntity, String> {
+
+    List<EventEntity> findAllBySentIsFalse();
+
+}

day026/src/main/java/com/pawelpluta/day026/jpa/JpaEventPublisherRepository.java

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+package com.pawelpluta.day026.jpa;
+
+import com.pawelpluta.day026.Event;
+import com.pawelpluta.day026.EventSupplier;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+
+@Repository
+class JpaEventPublisherRepository implements EventSupplier {
+
+    private final JpaEventEntityRepository repository;
+
+    JpaEventPublisherRepository(JpaEventEntityRepository repository) {
+        this.repository = repository;
+    }
+
+    @Override
+    public List<Event> fetchEventsToSend() {
+        return repository.findAllBySentIsFalse().stream().map(entity -> (Event) new Event.EventVO(entity.getId(), entity.getBody())).toList();
+    }
+}