Aggregate with MongoDB

0_README.md

Entity Event Sourced with Spring Boot and MongoDB

Profile.java

package dev.aleixmorgadas.eventsourcedmongo.domain;

import org.springframework.data.annotation.Id;
import org.springframework.data.annotation.PersistenceCreator;
import org.springframework.data.annotation.Transient;
import org.springframework.data.mongodb.core.mapping.Document;

import java.util.*;

@Document
public class Profile {
    @Id
    String id;
    @Transient
    final State state = new State();
    final List<Event> events = new ArrayList<>();

    public Profile(String id, String name) {
        apply(new Event.Created(id, name));
    }

    @PersistenceCreator
    Profile(String id, List<Event> events) {
        this.id = id;
        events.forEach(this::apply);
    }

    void apply(Event event) {
        events.add(event);
        // update with pattern matching in Java 21
        if (event instanceof Event.Created created) {
            on(created);
        } else if (event instanceof Event.AgeUpdated ageUpdated) {
            on(ageUpdated);
        }
    }

    void on(Event.Created created) {
        id = created.id;
        state.name = created.name;
    }

    void on(Event.AgeUpdated ageUpdated) {
        state.age = ageUpdated.age();
    }

    String name() {
        return state.name;
    }

    public static Profile of(String name) {
        return new Profile(UUID.randomUUID().toString(), name);
    }

    public int age() {
        return state.age;
    }

    public void withAge(int age) {
        apply(new Event.AgeUpdated(age));
    }

    static class State {
        String name;
        int age;
    }

    sealed interface Event {
        record Created(String id, String name) implements Event {}
        record AgeUpdated(int age) implements Event {}
    }
}

ProfileRepositoryTest.java

package dev.aleixmorgadas.eventsourcedmongo.domain;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
import org.testcontainers.containers.MongoDBContainer;
import org.testcontainers.junit.jupiter.Container;
import org.testcontainers.junit.jupiter.Testcontainers;
import org.testcontainers.utility.DockerImageName;

import static org.assertj.core.api.Assertions.assertThat;

@DataMongoTest
@Testcontainers
public class ProfileRepositoryTest {
    @Container
    @ServiceConnection
    static MongoDBContainer mongo = new MongoDBContainer(DockerImageName.parse("mongo:6.0.7"));
  
    @Autowired
    ProfileRepository repository;

    @Test
    void savesProfileIntoDB() {
        var profile = Profile.of("Aleix");
        profile.withAge(30);
        repository.save(profile);

        var id = profile.id;

        var savedProfile = repository.findById(id).orElseThrow();
        assertThat(savedProfile.events).hasSize(2);
        assertThat(savedProfile.name()).isEqualTo("Aleix");
        assertThat(savedProfile.age()).isEqualTo(30);
    }
}

ProfileTest.java

package dev.aleixmorgadas.eventsourcedmongo.domain;

import org.junit.jupiter.api.Test;

import static org.assertj.core.api.Assertions.assertThat;

public class ProfileTest {

    @Test
    void createsAProfile() {
        var profile = Profile.of("Aleix");

        assertThat(profile.name()).isEqualTo("Aleix");
        assertThat(profile.events).hasSize(1);
    }

    @Test
    void addsAge() {
        var profile = Profile.of("Aleix");
        profile.withAge(30);

        assertThat(profile.age()).isEqualTo(30);
        assertThat(profile.events).hasSize(2);
        assertThat(profile.events.get(1)).isInstanceOf(Profile.Event.AgeUpdated.class);
    }
}