The Todo List application is the hello world application for the Eventuate™ Platform. It illustrates how you can use the platform to write an application that uses Event Sourcing and Command Query Responsibility Segregation (CQRS). The Todo List application lets users maintain a todo list.
The Todo List application is a Java and Spring Boot application built using Eventuate™'s Event Sourcing based programming model.
Todos are implemented by an Event Sourcing-based TodoAggregate.
The aggregate's events are persisted in the Eventuate event store.
The application also maintains a materialized view of the data in MySQL.
Don't forget to take a look at the other Eventuate example applications.
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The following diagram shows the Todo List application architecture:
The application consists of the following:
- Todo List Server - a Java and Spring Boot-based server-side application that has a HATEAOS-style REST API for creating, updating and querying todo list items.
- MySQL database - stores a materialized/denormalized view of todo list items.
Note: for simplicity, the Todo List service is deployed as a monolithic server but as you will see below, it consists of several independent modules.
The Todo List server has a Spring MVC-based REST API for creating, updating and querying todo list items. The Todo List server is written using the Eventuate Client Framework for Java, which provides an event sourcing based programming model. The server persists todo list items as events in the Eventuate event store. The Todo List server also maintains a materialized view of the todo list in MySQL.
The following diagram shows the design of the server:
The application is structured using the Command Query Responsibility Segregation (CQRS) pattern. It consists of the following modules:
-
Command-side module - it handles requests to create and update (e.g. HTTP POST, PUT and DELETE requests) todo list items. The business logic consists of event sourcing based
Todoaggregates. -
Query-side module - it handles query requests (ie. HTTP GET requests) by querying a MySQL materialized view that it maintains. It has an event handler that subscribes to Todo events and updates MySQL.
There are two versions of the source code:
single-module- a single module Gradle project. It is the easiest to get started with.multi-module- a multi-module Gradle project. It illustrates how to use multiple modules to separate the command side code from the query-side code.
This is a Gradle project. However, you do not need to install Gradle since it will be downloaded automatically. You just need to have Java 8 installed.
The details of how to build and run the services depend slightly on whether you are using Eventuate SaaS or Eventuate Local.
First, must sign up to get your credentials in order to get free access to the SaaS version.
Next, build the application
./gradlew assemble
Next, you can launch the services using Docker Compose:
docker-compose build
docker-compose up -d
First, build the application
./gradlew assemble -P eventuateDriver=local
Next, launch the services using Docker Compose:
export DOCKER_HOST_IP=...
docker-compose -f docker-compose-eventuate-local.yml build
docker-compose -f docker-compose-eventuate-local.yml up -d
Note: You need to set DOCKER_HOST_IP before running Docker Compose.
This must be an IP address or resolvable hostname.
It cannot be localhost.
See this guide to setting DOCKER_HOST_IP for more information.
Once the application has started, you can use the application via the Swagger UI.
If you are running the multi-module version:
http://${DOCKER_HOST_IP}:8081/swagger-ui.html- the command-side servicehttp://${DOCKER_HOST_IP}:8082/swagger-ui.html- the query-side service
If you are running the single-module version:
http://${DOCKER_HOST_IP}:8080/swagger-ui.html- the monolithic application
Don't hesitate to create an issue or see