Types

In Sequent, events are stored as JSON in the event store. To be able to serialize and deserialize to the correct types, you are required to specify the type of an attribute.

This also gives Sequent the ability to check that the attributes in, for instance, Commands and ValueObjects are of the correct type.

Before a Command is executed, the CommandService ensures that the attributes are validated and parsed to the correct types if necessary.

Out of the box Sequent supports the following types:

1. String
2. Integer
3. Date
4. DateTime
5. Time
6. Boolean
7. Symbol
8. ValueObject
9. List
10. Sequent::Secret
11. BigDecimal

String

Usage: attrs name: String

Valid strings are nil and anything that can be to_s-ed. There are some invalid characters like "\0000" that Postgres can’t handle.

When a String is considered invalid, the error code invalid_string is added to the attribute in the ActiveModel Errors object during validation.

Integer

Usage attrs counter: Integer

Registers the following Validation:

validates_numericality_of :counter, only_integer: true, allow_nil: true, allow_blank: true

To accommodate user input, Integers passed as Strings are parsed automatically when a Command is passed to the CommandService.

Date:

Usage attrs created_at: Date

Accepts all Date objects. To accommodate user input, valid ISO 8601 date Strings are parsed automatically when a Command is passed to the CommandService.

DateTime

DEPRECATED Use Time instead

Usage attrs created_at: DateTime

Accepts all DateTime objects. To accommodate user input, valid ISO 8601 datetime Strings are parsed automatically when a Command is passed to the CommandService.

Time

Usage attrs created_at: Time

Accepts all Time objects. To accommodate user input, valid ISO 8601 datetime Strings are parsed automatically when a Command is passed to the CommandService.

Boolean:

Usage attrs confirmed: Boolean

Valid Booleans are true false and nil. To accommodate user input the values "true" and "false" are parsed to true and false automatically when a Command is passed to the CommandService.

Symbol:

Usage attrs user_type: Symbol

ValueObject

Usage:

class Money < Sequent::ValueObject
  attrs cents: Integer, currency: String
end

class MyEvent < Sequent::Event
  attrs amount: Money
end

Custom ValueObjects can contain other ValueObjects with attrs of the Types described here.

List

Usage: attrs names: array(String)

Lists can be a List of any Type described here.

Sequent::Secret

Usage: attrs password: Sequent::Secret

This is a special type designed to work with user input (HTML forms).

It will irreversibly hash the attribute that is of type Sequent::Secret using bcrypt.

Usage:

class CreateUser < Sequent::Command
  validates_presence_of :email, :password

  attrs email: String, password: Sequent::Secret
end

post '/create' do
  create_user = CreateUser.new(
    aggregate_id: Sequent.new_uuid,
    email: params[:email],
    password: params[:password],
  )

  Sequent.command_service.execute_commands create_user
end

class UserCommandHandler < Sequent::CommandHandler
  on CreateUser do |command|
    # 1. password is now of type Sequent::Secret
    # 2. the password is encrypted

  end
end

There is no need to use this in Events since those should always contain the hashed secret. Events can store these values in plain Strings.

BigDecimal

Usage: attrs amount: BigDecimal

Ruby’s BigDecimal. No special validations are added by default. The value is passed to BigDecimal.new(value) as is.