Model-Bound Operations

Arc supports minimal API-style endpoints for commands and queries, called model-bound operations. These endpoints are registered automatically by the Arc infrastructure and follow a convention-based naming scheme (Execute<TypeName>).

Because model-bound endpoints do not use traditional controller actions, the standard CommandResultOperationTransformer and QueryResultOperationTransformer transformers do not apply to them. The ModelBound.CommandOperationTransformer and ModelBound.QueryOperationTransformer fill this gap.

Registration

Model-bound transformers are included automatically when you call AddConcepts():

builder.Services.AddOpenApi(options => options.AddConcepts());

They can also be registered independently:

builder.Services.AddOpenApi(options => options.AddModelBoundOperationTransformers());

Command operations

The ModelBound.CommandOperationTransformer matches operations whose operationId starts with Execute and resolves the command type from the registered ICommandHandlerProviders.

For matched operations it:

1. Sets the requestBody to a schema of the command type.
2. Sets the 200 response schema to CommandResult or CommandResult<T> (depending on the handler return type).
3. Adds 400, 403, and 500 error response schemas.

// The command is automatically discovered and the endpoint is documented
[Command]
public record CreateInvoice(CustomerId Customer, decimal Amount)
{
    public Task Handle() { ... }
}

Query operations

The ModelBound.QueryOperationTransformer matches operations whose operationId starts with Execute and resolves the query performer from the registered IQueryPerformerProviders.

For matched operations it:

1. Adds each query parameter from the performer’s parameter list as a query string parameter.
2. Adds paging and sorting parameters when IQueryPerformer.SupportsPaging is true.
3. Sets the 200 response schema to QueryResult.
4. Adds 400, 403, and 500 error response schemas.

Pagination and sorting parameters

For query performers that support paging, the following query parameters are added:

Parameter	Type	Description
sortby	string	Field name to sort by
sortDirection	string (asc | desc)	Sort direction
pageSize	integer	Number of items per page
page	integer	Page number (0-based)