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Cratis

ARC0023: Generated value declared outside a command Handle method

Rule

Section titled “Rule”

ARC0023 reports [GeneratedValue] where the declaration is invalid regardless of which commands exist in this or another assembly:

  • The method is not named Handle, including Provide and other method names.
  • The method is static, including a static Handle.
  • The method belongs to a [ReadModel] type, regardless of its name.
  • The method belongs to a controller: a type deriving from Microsoft.AspNetCore.Mvc.ControllerBase, or marked [ApiController] or [Controller]. An action named Handle is still reported.

Inherited read-model and controller declarations are recognized. Default severity: Error.

An instance Handle() that no command uses is not reported. Its attribute is inert: the runtime never reads it. This applies to public base types, sealed non-command types, and inaccessible types alike. The analyzer does not try to predict whether another assembly will define a command subclass.

Only a model-bound command’s effective Handle() participates in generation. When a command uses an inherited handler, ARC0022, ARC0024, and ARC0025 still check that command’s generated parameters.

Diagnostic example

Section titled “Diagnostic example”

The examples use this identifier, the same declaration as in generated values:

using System;
using Cratis.Arc.Commands.ModelBound;
using Cratis.Concepts;


public record CartId(Guid Value) : ConceptAs<Guid>(Value), IGeneratable<CartId>
{
    public static CartId New() => new(GenerateValue.Uuid());
}

Compile each alternative below together with it, one at a time; the first intentionally produces ARC0023.

[Command]
public record AllocateCartId
{
    public CartId Provide([GeneratedValue] CartId cartId) => cartId;


    public CartId Handle(CartId cartId) => cartId;
}

Fix

Section titled “Fix”

Move generation to the handler parameter:

[Command]
public record AllocateCartId
{
    public CartId Handle([GeneratedValue] CartId cartId) => cartId;
}

For an ordinary service or read model dependency, remove [GeneratedValue] instead. Arc resolves those dependencies through the normal Provide and dependency injection path.

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