c# - Recommended ServiceStack API Structure

Question

I'm trying work out the best way to structure our API; we have Reviews which we've setup in a standard REST structure (list one, list all, create, update etc). Where it doesn't quite fit the examples is: each review can be linked to one or more other types e.g. Event, Location or Thing.

My thinking is the urls would be along the lines of: /event/reviews/ (or the reverse of this e.g. /reviews/event/) /location/reviews/ /thing/reviews/

The issue I can see however is the "GET" for each of these should return the parent object i.e. an Event.

So using ServiceStack, what's the best way to handle this scenario? Is it to create a custom service for each data request rather than abusing the out-of-the-box REST setup or have I missed something more fundamental?

Answer 1

Firstly "Best" solution is a fairly subjective term. I'll generally aim for DRY, re-usable, performant solutions that promotes the least effort, friction and chattiness, whilst others may define "Best" in how closely it follows the principles of REST. So you will get varied responses depending on what the goals are. I can only offer how I would approach it.

ServiceStack service implementations are de-coupled from their custom routes

One thing to keep in mind is how you define and design your services in ServiceStack are fairly de-coupled in how you expose them, since you can expose your services under any custom route. ServiceStack encourages a message-based design so you should give each operation a distinct message.

Use a logical / hierarchical Url structure

I'd use a logical Url structure that I aim to represent the identifier of a noun, which is hierarchically structured, i.e. the parent path categorizes your resource and gives it meaningful context. So in this case if you wanted to expose Events and reviews my inclination is to go with following url structure:

/events             //all events
/events/1           //event #1
/events/1/reviews   //event #1 reviews

Each of these resource identifiers can have any HTTP Verb applied to them

Implementation

For the implementation I generally follow a message-based design and group all related operations based on Response type and call context. For this I would do something like:

[Route("/events", "GET")]
[Route("/events/category/{Category}", "GET")] //*Optional top-level views
public class SearchEvents : IReturn<SearchEventsResponse>
{
   //Optional resultset filters, e.g. ?Category=Tech&Query=servicestack
   public string Category { get; set; } 
   public string Query { get; set; }
}

[Route("/events", "POST")]
public class CreateEvent : IReturn<Event>
{
   public string Name { get; set; }
   public DateTime StartDate { get; set; }
}

[Route("/events/{Id}", "GET")]
[Route("/events/code/{EventCode}", "GET")] //*Optional
public class GetEvent : IReturn<Event>
{
   public int Id { get; set; }
   public string EventCode { get; set; } //Alternative way to fetch an Event
}

[Route("/events/{Id}", "PUT")]
public class UpdateEvent : IReturn<Event>
{
   public int Id { get; set; }
   public string Name { get; set; }
   public DateTime StartDate { get; set; }
}

And follow a similar pattern for Event reviews

[Route("/events/{EventId}/reviews", "GET")]
public class GetEventReviews : IReturn<GetEventReviewsResponse>
{
   public int EventId { get; set; }
}

[Route("/events/{EventId}/reviews/{Id}", "GET")]
public class GetEventReview : IReturn<EventReview>
{
   public int EventId { get; set; }
   public int Id { get; set; }
}

[Route("/events/{EventId}/reviews", "POST")]
public class CreateEventReview : IReturn<EventReview>
{
   public int EventId { get; set; }
   public string Comments { get; set; }
}

The implementation should be fairly straight forward based on these messages, which (depending on code-base size) I would organize in 2 EventsService and EventReviewsService classes. I should note that I use pluralization for Service Request DTO names myself to avoid clashing with data models of the same name.

Although I've separated UpdateEvent and CreateEvent here, I will sometimes will merge them into a single idempotent StoreEvent operation if the use-case permits.

Physical Project Structure

Ideally the root-level AppHost project should be kept lightweight and implementation-free. Although for small projects with only a few services it's ok for everything to be in a single project and to simply grow your architecture when and as needed.

For medium-to-large projects we recommend the physical structure below which for the purposes of this example we'll assume our Application is called EventMan.

The order of the projects also show its dependencies, e.g. the top-level EventMan project references all sub projects whilst the last EventMan.ServiceModel project references none:

- EventMan
    AppHost.cs              // ServiceStack ASP.NET Web or Console Host Project

- EventMan.ServiceInterface // Service implementations (akin to MVC Controllers)
    EventsService.cs
    EventsReviewsService.cs

- EventMan.Logic            //For larger projs: pure C# logic, data models, etc
    IGoogleCalendarGateway  //E.g of a external dependency this project could use

- EventMan.ServiceModel     //Service Request/Response DTOs and DTO types
    Events.cs               //SearchEvents, CreateEvent, GetEvent DTOs 
    EventReviews.cs         //GetEventReviews, CreateEventReview
    Types/
      Event.cs              //Event type
      EventReview.cs        //EventReview type

With the EventMan.ServiceModel DTO's kept in their own separate implementation and dependency-free dll, you're freely able to share this dll in any .NET client project as-is - which you can use with any of the generic C# Service Clients to provide an end-to-end typed API without any code-gen.

---

Update

• This recommended project structure is now contained in all ServiceStackVS' VS.NET Templates.

• The Simple Customer REST Example has a small self-contained, real-world example of creating a simple REST Service utilizing an RDBMS.