OData and WCF Data Services

This week we started investigating OData and WCF data services as a way to easily expose and query a remote database. OData, the Open Data Protocol is a protocol for querying and updating data over using Http and AtomPub. Visual studio 2010 and .NET 4.0 come with rich support to both produce and consume data using the Open Data Protocol. This post is a tutorial on how to set up a web service that exposes OData, and how to query it from a client application.

Prerequisites

Exposing data as Odata

Create a new ASP.NET Web application

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Create the Entity Data Model for the Northwind database

The Entity Data Model will be the base for the WCF Data Service that will expose the Northwind data in the OData format

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Here we can choose which Tables, Views and Stored Procedures will be exposed

Finish creates the Entity Data Model for the Northwind database

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Create a new WCF Data Service

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The NorthwindService inherits from the DataService with as generic parameter the EntityDataModel we want to expose, in this case the NorthwindEntities we just created.

By default noone can do anything, we first need to set access rules for our entities.

The easyest way to do this is to expose all entities with read-all rights:

 

config.SetEntitySetAccessRule("*", EntitySetRights.AllRead);

 

If the Entity Data Model is in a different assembly you’ll need to add a reference, and make sure the connectionstring is in the web.config of the referencing project

 

Visiting the service now shows the exposed data:

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Consuming the data

To use the data exposed by the web service we create a client application.

Add a Service Reference to the web service.

For testing, there is always a public Northwind web service available on http://services.odata.org/Northwind/Northwind.svc/

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This generates a web service proxy.

New is that this also generates a DataServiceContext.

Using the DataServiceContext we can query the data service through a linq provider.

The following extremely simple example print a list with the Name and Unit Price of all available products.

 

class Program {    staticvoid Main(string[] args)    {        string url ="http://localhost:40171/NorthwindService.svc/";        var context =new NorthwindEntities(new Uri(url));         var someProducts = from p in context.Products                           where!p.Discontinued                           select p;         foreach (var product in someProducts)        {            Console.Out.WriteLine("{0} - {1}",product.ProductName,product.UnitPrice);        }        Console.Read();    } }

 

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Download the sample code:

http://www.orbitone.com/SiteCollectionDocuments/Northwind%20OData%20Service%20Sample.zip

 

More information, samples, articles and tutorials can be found on http://www.odata.org/

Some more links to get you started:


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