Macro for defining a mapping shared across every read model variant of a given identity, without repeating it on each variant module.

A global handler is never registered as a projection on its own. Its from/2 mappings are merged into every read model or declarative projection whose variant_of/2 names the same identity, before that variant's own non-entering events are reclassified into update-only joins - so a shared mapping for a non-entering event is turned into an update-only join exactly like a mapping declared directly on the variant.

Quick Example

defmodule MyApp.Projections.WorkItemTitleHandler do
  use Chronicle.Projections.GlobalHandler, identity: MyApp.ReadModels.WorkItem

  from MyApp.Events.TitleChanged,
    set: [title: :title]
end

A mapping that targets a member some variant lacks is a declaration error (Chronicle.Projections.GlobalHandlerPropertyNotOnVariant), raised at registration time - not a silently skipped mapping.

Registering with Chronicle.Client

{Chronicle.Client,
  ...
  global_handlers: [MyApp.Projections.WorkItemTitleHandler]}

Or use otp_app: auto-discovery - modules that export __chronicle_global_handler__/1 are discovered automatically.