---
title: 'CHR0064: Invalid read model event stream'
editUrl: https://github.com/Cratis/Chronicle/edit/main/Documentation/code-analysis/CHR0064.mdx
description: CHR0064 rejects invalid per-stream read model declarations and confusion between the generic and non-generic EventStream attributes.
lastUpdated: 2026-10-15T00:00:00.000Z
---


## Rule description

A per-stream read model must name one stream declared by an `IEventSource` definition and keep the event source ID as its model key. It is implicitly passive and cannot be reducer-backed.

| Declaration | Diagnostic |
| --- | --- |
| `[EventStream<TSource>(stream)]` names an undeclared stream, an empty stream or `All` | Error |
| Non-generic `[EventStream(stream)]` on a type that is not an `IEventSource` | Error; the attribute would not scope a read model |
| Generic `[EventStream<TSource>(stream)]` on an `IEventSource` | Error; use the non-generic declaration there |
| Generic attribute on a self-reducing model, a classic reducer, or a model with a visible `IReducerFor<T>` | Error; reducers cannot fold one stream |
| Fluent `UsingKeyFromContext(context => context.EventStreamId)` on the declared model | Error; a month alone collides across owners |

The analyzer reports statically visible declarations and stream-key mappings. Runtime registration validates the declaration and the projection's root key as well.

## Severity

Error

## How to fix

Put the non-generic attribute from `Cratis.Chronicle.EventSources` on the event source definition. Put the generic attribute from `Cratis.Chronicle.ReadModels` on a source-keyed projection model and name a stream the definition declares. Remove stream-key redirection and reducer handlers from that model. Keep a separate whole-source reducer if you need one.

The [monthly-limit example](/chronicle/read-models/per-stream/#declare-the-model-and-guard-the-decision) shows both attributes together and the stream-aware reads. There is no automatic code fix: choosing which history defines a rule is a correctness decision.

## Related topics

- [Read models scoped to one event stream](/chronicle/read-models/per-stream/)
- [Decision-consistent reads](/chronicle/read-models/decision-reads/)
- [Defining event sources](/chronicle/event-sources/defining/)