CHR0003: Model bound projection attribute must reference event type with [EventType] attribute

Rule Description

Model bound projection attributes (such as FromEventAttribute<TEvent>, RemovedWithAttribute<TEvent>, etc.) must reference types that are marked with the [EventType] attribute.

Severity

Error

Example

Violation

// Missing [EventType] attribute
public record ProductAdded(Guid ProductId, string Name, decimal Price);

// CHR0003: Type 'ProductAdded' must be marked with [EventType] attribute
[FromEvent<ProductAdded>]
public class ProductReadModel
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

Fix

using Cratis.Chronicle.Concepts.Events;

[EventType]
public record ProductAdded(Guid ProductId, string Name, decimal Price);

// Now valid
[FromEvent<ProductAdded>]
public class ProductReadModel
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

Applicable Attributes

This rule applies to the following model bound projection attributes:

• FromEventAttribute<TEvent>
• RemovedWithAttribute<TEvent>
• RemovedWithJoinAttribute<TEvent>
• JoinAttribute<TEvent>
• ChildrenFromAttribute<TEvent>
• FromEveryAttribute<TEvent>

Quick Fix

The analyzer provides a code fix that automatically adds the [EventType] attribute to the referenced event type.

Why This Rule Exists

Model bound projections use attributes to define how events map to read models. These attributes must reference valid event types to ensure:

• Proper event-to-model mapping
• Correct projection materialization
• Type-safe projection definitions
• Accurate event handling

Related Rules

• CHR0001: Event sequence append operations
• CHR0002: Declarative projection event types