Chekov

Table of Contents

• Features
• Getting started
• FAQ
• Need help?
• Contributing

Features

• Postgres EventStore backend
• Dispatch Command to Aggregate or CommandHandler
• Generate Event from Aggregate and persist them
• Apply Event to Aggregate
• Store and notify Event with subscriptions
• Dispatch Event to EventHandler

Getting started

Choosing an EventStore backend

Chekov works only with Postgres backend for now (and InMemory for test purpose). The choice is easy to make!

But some more backends need to be implemented, see the related issue.

Defining Aggregates

An Aggregate is a struct that hold a domain state. Here's an example of a UserAggregate:

#[derive(Default, Aggregate)]
#[aggregate(identity = "user")]
struct User {
    user_id: Option<Uuid>,
    account_id: Option<Uuid>,
}

/// Define an Executor for the `CreateUser` command
/// The result is a list of events in case of success
impl CommandExecutor<CreateUser> for User {
  fn execute(cmd: CreateUser, _state: &Self) -> Result<Vec<UserCreated>, CommandExecutorError> {
    Ok(vec![UserCreated {
      user_id: cmd.user_id,
      account_id: cmd.account_id,
    }])
  }
}

/// Define an Applier for the `UserCreated` event
/// Applier is a mutation action on the aggregate
#[chekov::applier]
impl EventApplier<UserCreated> for User {
  fn apply(&mut self, event: &UserCreated) -> Result<(), ApplyError> {
    self.user_id = Some(event.user_id);
    self.account_id = Some(event.account_id);

    Ok(())
  }
}

Defining Commands

You need to create a struct per command, any type of struct can implement Command but we advise to use struct for a better readability.

A command can only produce (or not) one type of events and it targets a single Aggregate. A command must have a single and unique identifier that is used to route the command to the right target.

#[derive(Debug, Command)]
#[command(event = "UserCreated", aggregate = "User")]
struct CreateUser {
    #[command(identifier)]
    user_id: Uuid,
    account_id: Uuid,
}

Defining Events

An Event can be a struct or an enum.

#[derive(Event, Deserialize, Serialize)]
struct UserCreated {
    user_id: Uuid,
    account_id: Uuid,
}

Defining Saga

Not implemented yet

FAQ

Does Chekov is production ready ?

No its not. Some critical part of the project are still not implemented and a lot of code needs to be refactored before that.

Need Help?

Feel free to open issue in case of bugs or features requests. Discussions are also a great starts if you have issue that are not bugs nor features requests.

Contributing

The project is really early staged and have a lot of pending tasks, one major tasks is to produce a roadmap or some issues that can be used to expose the project vision. Feel free to open a Discussions around it if you want !