What is the simplest way to convert a WCF Data Services OData provider to Web API?

Question

I'm currently looking at the feasibility of converting our current WCF Data Services OData provider to Web API OData.

I'm just a little confused at the OData implementation for Web API. With WCF Data Services it sits over the top of our ADO.Net entity model which exposes a bunch of tables from the SQL Server backend, i.e. you give WCFDS the ADO model to generate and then you have access to all of the tables through the standard OData syntax.

With Web API from all reading so far do we create a controller or separate actions for every table/object that we want to expose? Am I missing something? Is there just a way where the OData Web API controller can just expose the entire model from the ADO Data model? Having to create a action for every table would be a mess and overkill.

Currently if we need to add a table we just map it in the EDMX and WCFDS will automatically expose it as it's mapped to the entire context of the model.

Answer 1

Generating the model(s)

You can:

• Use the convention model builder from ASP.NET Web API. This generates a different model than what EF's own convention model builder produces: an EdmLib IEdmModel. See this question though if you're using model-first or database-first. This method seems really backwards, and it is, but it mostly works.
• Serialize the EF model and rebuild it as an IEdmModel (see this question). Again this is really inefficient. If you're using model-first or database-first, you'll want to just deserialize the EDMX file to build the IEdmModel. It still produces a different model internally, but at least the CDSL is a more stable format than CLR code conventions, so you'll probably have less surprises than you'd get when using two different convention-based model builders.

The reason for this is that ASP.NET Web API OData extensions use EdmLib, while EF uses its own code, and there is no plan to make them work together. Maybe you'll find this rant useful if you're curious.

Working on the API

Once you've generated the model from a unique source (so that you can work on your model from a single place), you'll indeed have to create a controller per entity, basically. The point of Web API is not to build things automagically, but to offer flexibility to the developer. The EntitySetController helps reducing redundancy, but it won't offer everything out of the box.

Taking a step back

In the rant mentioned above, I also talk about the difference between a service-layer API and a data-layer API. ASP.NET Web API is better suited for services, while OData makes services awkward. On the other hand, OData makes data access a breeze (essentially being like a RESTful SQL) and by virtue of being directly attached to the data model, can automate a lot of things as you saw with WCF Data Services. ASP.NET Web API with OData extensions sits in the middle, and its value is not universally agreed upon (using certain bits of OData URI syntax on service APIs is certainly useful though).

Don't get too hyped up by the recent buzz around ASP.NET Web API, it and WCF Data Services are very different beasts and run on different layers in your design. Indeed, in a multi-tier architecture, you could very well see a service API built using ASP.NET Web API sitting on top of an OData API built using WCF Data Services.

My advice is think carefully about what you're trying to build, and depending on the answer, either choose ASP.NET Web API and embrace the fact that the API you expose will be very different from a data-centric OData API, or stick with WCF Data Services.

A possible plan

You can find a lot of material on the web about service-layer APIs on the web by searching for terms like "non-CRUD web/RESTful/hypermedia API" or by comparing products like ServiceStack, which advocate for less data-oriented APIs.

If you're still unsure about the nature of your project, prototype it.

• If you end up with a bunch of essentially identical controllers with Web API, each mapped to exactly one entity, then your API is heavily data-oriented. Go with WCF Data Services.
• If you end up with a lot of OData Actions and awkward entities with WCF Data Services, then you need more domain logic on the server-side of the API, and data-orientation doesn't offer you enough. Go with Web API. A good rule of thumb here is to treat OData actions just like you treat stored procedures in a SQL DBMS. Actually, treat any OData server as a DBMS, because that's what they are. If you wouldn't put it behind a SQL interface, don't put it behind an OData interface.

Important (Update)

It was announced on March 27th 2014 that WCF Data Services would be discontinued by Microsoft in favor of ASP.NET Web API. To handle the "data-layer" use-cases I've exposed here, Microsoft has said that it is planning to extend ASP.NET Web API. Some community efforts are also underway. WCF Data Services will also be open-sourced at some point, so it's not impossible that a new maintainer will takeover, though it's uncertain.