Polecat.AspNetCore

Polecat ships a small companion package, Polecat.AspNetCore, with helpers for ASP.NET Core development. The main feature is a set of typed IResult wrappers that let you return Polecat documents and event-sourced aggregates directly from Minimal API endpoints with correct status codes, content types, and OpenAPI metadata.

Install the NuGet package:

PM> Install-Package Polecat.AspNetCore

Typed Streaming Result Types

For Minimal API endpoints (and frameworks like Wolverine.Http that dispatch any IResult return value), Polecat.AspNetCore ships three typed result wrappers:

Type	Source	Response shape	404 on miss?
StreamOne<T>	IQueryable<T> — document query	Single T	yes
StreamMany<T>	IQueryable<T> — document query	JSON array T[]	no (empty array = 200)
StreamAggregate<T>	IQuerySession + stream id — event-sourced	Single T	yes

Each type implements both IResult (so ASP.NET dispatches it via ExecuteAsync) and IEndpointMetadataProvider (so OpenAPI generators see the right response shape).

StreamOne — single document with 404 on miss

app.MapGet("/issues/{id:guid}",
    (Guid id, IQuerySession session) =>
        new StreamOne<Issue>(session.Query<Issue>().Where(x => x.Id == id)));

Returns 200 application/json with the document JSON on a hit, 404 on a miss. Content-Length and Content-Type are set automatically.

StreamMany — JSON array

app.MapGet("/issues/open",
    (IQuerySession session) =>
        new StreamMany<Issue>(session.Query<Issue>().Where(x => x.IsOpen)));

Returns 200 application/json with a JSON array body. An empty result set yields [], not a 404.

StreamAggregate — event-sourced aggregate (latest)

app.MapGet("/orders/{id:guid}",
    (Guid id, IQuerySession session) =>
        new StreamAggregate<Order>(session, id));

Returns 200 application/json with the latest projected aggregate state, or 404 if no stream exists. A constructor overload accepts string ids for stores configured with string-keyed streams.

StreamOne vs StreamAggregate

• StreamOne<T> is for regular documents — objects stored via session.Store() and queried with session.Query<T>().
• StreamAggregate<T> is for event-sourced aggregates — Polecat rebuilds (or reads the snapshot of) the latest aggregate state from events before writing the response.

Customizing status code and content type

All three types expose init-only properties:

app.MapPost("/issues",
    (CreateIssue cmd, IQuerySession session) =>
        new StreamOne<Issue>(session.Query<Issue>().Where(x => x.Id == cmd.IssueId))
        {
            OnFoundStatus = StatusCodes.Status201Created,
            ContentType = "application/vnd.myapi.issue+json"
        });

TIP

Unlike Marten.AspNetCore, Polecat does not currently offer a deserialize-free raw-JSON streaming path. The streaming helpers materialize documents via the regular query path and serialize through System.Text.Json. This still eliminates the endpoint boilerplate (null-check, status code, content type, OpenAPI metadata). A future enhancement will add a true streaming path.