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:
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.