Constraints

Constraints are shared Chronicle behavior. The shared docs cover constraint concepts, model-bound constraints, declarative constraints, and client-tabbed examples.

• Constraints
• Understanding constraints
• Elixir client setup

Scoping uniqueness checks

unique/2 accepts a :scope option that narrows a uniqueness check to values observed at append time along one or more dimensions, instead of checking globally across the whole event store. Mirrors the C# client’s IConstraintBuilder.PerEventSourceType() / PerEventStreamType() / PerEventStreamId().

:scope takes an atom — :per_event_source_type, :per_event_stream_type, or :per_event_stream_id — or a list of them to scope along more than one dimension at once:

defmodule MyApp.Events.EmailChanged do
  use Chronicle.Events.EventType, id: "email-changed"

  defstruct [:email]

  # Unique only among events from the same event source type — the same email value
  # may repeat across different event source types (e.g. an employee and a customer
  # can share an email without tripping this constraint).
  unique(:email, scope: :per_event_source_type)
end

Without :scope, uniqueness is checked globally, as before.