Polecat Operation Side Effects

TIP

You can certainly write your own IPolecatOp implementations and use them as return values in your Wolverine handlers

INFO

This integration also includes full support for the storage action side effects model when using Polecat with Wolverine.

The Wolverine.Polecat library includes some helpers for Wolverine side effects using Polecat with the IPolecatOp interface:

/// <summary>
/// Interface for any kind of Polecat related side effect
/// </summary>
public interface IPolecatOp : ISideEffect
{
    void Execute(IDocumentSession session);
}

The built in side effects can all be used from the PolecatOps static class like this HTTP endpoint example:

[WolverinePost("/invoices/{invoiceId}/pay")]
public static IPolecatOp Pay([Entity] Invoice invoice)
{
    invoice.Paid = true;
    return PolecatOps.Store(invoice);
}

There are existing Polecat ops for storing, inserting, updating, and deleting a document. There's also a specific helper for starting a new event stream as shown below:

public static class TodoListEndpoint
{
    [WolverinePost("/api/todo-lists")]
    public static (TodoCreationResponse, IStartStream) CreateTodoList(
        CreateTodoListRequest request
    )
    {
        var listId = CombGuidIdGeneration.NewGuid();
        var result = new TodoListCreated(listId, request.Title);
        var startStream = PolecatOps.StartStream<TodoList>(listId, result);

        return (new TodoCreationResponse(listId), startStream);
    }
}

The major advantage of using a Polecat side effect is to help keep your Wolverine handlers or HTTP endpoints be a pure function that can be easily unit tested through measuring the expected return values. Using IPolecatOp also helps you utilize synchronous methods for your logic, even though at runtime Wolverine itself will be wrapping asynchronous code about your simpler, synchronous code.

Returning Multiple Polecat Side Effects

Wolverine lets you return zero to many IPolecatOp operations as side effects from a message handler or HTTP endpoint method like so:

public static IEnumerable<IPolecatOp> Handle(AppendManyNamedDocuments command)
{
    var number = 1;
    foreach (var name in command.Names)
    {
        yield return PolecatOps.Store(new NamedDocument{Id = name, Number = number++});
    }
}

Wolverine will pick up on any return type that can be cast to IEnumerable<IPolecatOp>, so for example:

• IEnumerable<IPolecatOp>
• IPolecatOp[]
• List<IPolecatOp>