After having playing with the current bits of OpenRasta (OR) for a while, I am now able to see great advantages in using this framework over other existing frameworks for building RESTful services such as WCF or the ASP.NET MVC.
Let’s explore some of the good features that make OpenRasta an excellent alternative at the moment of developing RESTful services.
1. Clean separation of resource representation from service implementation
If we take a look at a service implementation in OR, the operations in a handler receive or return a resource, but they never specify the final representation of that resource. Resource representation is a pure responsibility of the encoders configured for service implementation (a handler in OR).
In that way, we have a service implementation completely reusable for different resource representations.
public class CustomerHandler
{
public OperationResult Get(int customerId)
{
return new OperationResult.OK
{
ResponseResource = "Customer with id " + customerId
};
}
}
Once we have the service implementation, we only need to configure the encoders for that service, which could be encoders for Xml, Json, Atom or any other representation. You are free to configure all the encoders you want for the same handler.
ConfigureServer(() => ResourceSpace.Has.ResourcesOfType<Customer>()
.AtUri("/customer/{customerId}")
.HandledBy<CustomerHandler>()
.AndTranscodedBy<OpenRasta.Codecs.JsonDataContractCodec>(null));
This is a different story in WCF. First of all, the content type (Xml or Json) has to be specified as part of the operation definition. If we want to support different content types, we need to replicate the same operation only to change the content type. Although this point has been improved considerably in WCF 4.0, some service implementations are still absolutely tied to the resource representation. For example, an operation that returns syndications feeds. In WCF, we have to return a concrete implementation of System.ServiceModel.Syndication.SyndicationFeedFormatter. It is not a simple as return a collection of entities or resources and specify somewhere that we want to represent them as entries in a feed.
This works much better in ADO.NET data services, where you can just return a resource or a collection of resources, and the framework itself will chose the best representation according to what the client initially sent in the “Accept” header. That representation could be Json or Atom, nothing changes in the service implementation (which is also automatically implemented). However, ADO.NET data services provide few extensibility points today for injecting custom code, and that is probably a good reason to move to OpenRasta.
2. URI resolution
In OpenRasta, the URI resolution to a handler is also part of the service configuration. This gives a great flexibility to have many URIs that resolve to the same resource instance.
A typical example is a parent-child relationship, for instance, a customer/orders relationship.
You might want to have different URIs to get access to the orders,
Customer/1/Orders/1 => Give me the order number 1 for the customer with ID 1
Or you might want to access to the order directly
Orders/1 => Give me the order number 1
In OR, you have a single handler implementation for orders (order is the resource in this case), and multiple URIs that resolve to an operation in that particular handler.
ConfigureServer(() => ResourceSpace.Has.ResourcesOfType<Order>()
.AtUri("/customer/{customerId}/Orders/{orderId}")
.AndAt("/orders/{orderId}")
.HandledBy<OrderHandler>()
.AndTranscodedBy<OpenRasta.Codecs.JsonDataContractCodec>(null));
This is a problem in WCF because the URI template is tied to the operation definition, if you want to have different URIs for the same resource, you basically have to copy/paste the same operation just to change the URIs.
[WebGet(UriTemplate="/Orders/{orderId}")]
public Order GetOrderById(int orderId)
{
//implementation
}
[WebGet(UriTemplate = "/Customers/{customerId}/Orders/{orderId}")]
public Order GetCustomerOrder(int customerId, int orderId)
{
//implementation
}
So, you will have as many operations as URI and content types you want to support in the service.
