# `Chronicle.ReadModels.DecisionReadRefused`
[🔗](https://github.com/Cratis/Chronicle.Elixir/blob/main/lib/chronicle/read_models/decision_read_refused.ex#L4)

Raised when a read model's shape, or the requested stream scope, is not safe to guard a
decision with.

`:reason` mirrors the C# client's `DecisionReadRefusalReason`:

  * `:reducer` — the model is produced by an actively-observed reducer. Only a **passive**
    reducer (`use Chronicle.Reducers.Reducer, active: false`) can back a decision read.
  * `:join` — the projection declares `join/2` or `removed_with_join/2`. A joined read can
    change from an event outside the guarded event source, which the guard cannot express.
  * `:hierarchy` — the projection declares `children/2`. Nested/child collections are not
    representable as a single concurrency scope.
  * `:not_event_log` — the read model does not project from `"event-log"` (an `:event_sequence`
    override), or is not a recognized read model/reducer at all.
  * `:open_ended_event_types` — the projection declares `from_every/1`: it would have to guard
    against every event type ever appended, which Chronicle's `ConcurrencyScope` cannot express.
  * `:no_event_types` — the admitted shape resolves to no event types at all.
  * `:not_event_source_keyed` — a `from`/`removed_with` clause declares a `:key` other than the
    default `"$eventSourceId"` (a composite key, an event-context key, or similar).
  * `:unsupported_event_type_id` — one of the model's event type ids contains a comma, which
    cannot be told apart from an id list on the wire.
  * `:all_streams_not_supported` — a stream-scoped read was asked for the default stream (an
    empty or `"All"` event stream type) instead of a specific one.
  * `:stream_scope_not_supported` — the kernel reported the read model instance as not
    stream-scoped (`StreamScoped: false`), so a stream-scoped guard cannot be built from it.
  * `:fold_incomplete` — after 3 attempts, the read model still had not caught up to events
    already visible for its key/types; the read could not be made deterministic.

# `reason`

```elixir
@type reason() ::
  :reducer
  | :join
  | :hierarchy
  | :not_event_log
  | :open_ended_event_types
  | :no_event_types
  | :not_event_source_keyed
  | :unsupported_event_type_id
  | :all_streams_not_supported
  | :stream_scope_not_supported
  | :fold_incomplete
```

---

*Consult [api-reference.md](api-reference.md) for complete listing*