Command

Commands form the API of your domain. Like Events, they are simple data objects. Commands have descriptive names describing the intent of what you are trying to achieve, for example CreateUser or SendInvoice. Commands inherit from Sequent::Command. Additionally you can add Validations to commands to ensure correctness. Sequent uses ActiveModel::Validations to enable validations.

An example of a CreateUser Command, with basic validations:

class CreateUser < Sequent::Command
  attrs firstname: String, lastname: String
  validates_presence_of :firstname, :lastname
end

Commands, like Events, are also stored in the EventStore.

Typically when building a web application, you will bind an html form to a Command. You then have to pass it into the CommandService. The CommandService will only execute valid Commands. When a Command is valid, the CommandHandlers registered and interested in this Command will be invoked. When a Command is not valid, a Sequent::Core::CommandNotValid will be raised containing the validation errors.