Programming with SQL Azure : Record Navigation in WCF Data Services

Let's talk a few more minutes about the WCF Data Service you built and how you can use that to navigate through records. Record navigation is one of the things that really gets me excited about WCF Data Services. Let's dive right in.

If your project is still running, stop the project and open the Solution Explorer and navigate to the data service. For simplicity, you'll do this right from the solution. Right mouse click the data service and select View in Browser. The service will fire up and what you see is a REST (Representational State Transfer) based service on top of your relational database, a mere XML representation of the service and the entities exposed via the service, shown in Figure 1. You see the entities listed because you set the entity set rights to ALL. If you were to go back to the code a few pages back where you set the entity set rights, and comment those lines out, you would not see the entities listed (Docs, TechGeoInfoes, and Users).

Figure 1. Viewing the WCF Data Service via REST

The question though, is how do you view the data that you really want to see. The answer is simple. Specify an entity at the end of your URI, and you'll see data for that entity. For example, specify the following URI to see data on the Users entity:

http://localhost:51176/TechBioDataService.svc/Users

Take care to get the case correct. Entity names are case sensitive. Specify users instead of Users, and you'll get a "The webpage cannot be found" error message.

Take time out now to mistype an entity name and see the resulting message. That way you'll more readily recognize the problem when you make same mistake inadvertently. Sooner or later, you all make that mistake.

1. Disabling Internet Explorer's Feed Reading View

At this point you either get an XML representation of the data in the Users table, or the web page shown in Figure 2. If it's the latter, then you need to go turn off the feed reading view in Internet Explorer IE. That is because IE thinks that the data coming back is the type you would get in an RSS feed. You can see in the message that the browser thinks you're trying to view an RSS feed.

Figure 2. RSS Feed Page

To fix the RSS feed issue you need to turn off this feature in Internet Explorer. With IE open, from the Tools menu select Options which open the Internet Options dialog. This dialog has a number of tabs along the top which you might be familiar with. Select the Content tab and on that tab click the Settings button under Feeds and Web Slices.

Clicking the Settings button will display the Settings dialog, and on this dialog you need to uncheck the Turn on feed reading view checkbox, shown in Figure 3. Click OK on this dialog and the Internet Options dialog.

Figure 3. Disabling Feed Viewing

2. Viewing the Final Results

Back on your web page, press F5 to refresh the page. What you should get back now is a collection of Users, shown in Figure 4, by querying the underlying database for the Users.

However, you aren't done yet because there is still so much more you can do here. For example, the page you're currently looking at displays all the Users, but what if you want to return a specific user?

Looking at the data you can see that the each record contains the id of the specific row, and you can use that to your advantage by including that in your URI. For this example let's use ID 113. Modify the URI by appending the number 113 to the end of the URI enclosed in parenthesis, as shown in Figure 5.

By loading the URI which includes the id of a specific record, I can now drill down further and return just the record I am looking for. This is just like applying a WHERE clause to a T-SQL query, in this case WHERE ID = 113. In this case I have queried the underlying store for a specific user by passing the appropriate ID in the URI.

Additionally I can return a specific field by adding the field I want to the URI, such as:

http://localhost:51176/TechBioDataService.svc/Users(113)/Name

Specifying the specific field along with the id will return just the field you request. In the code snipped above, the value in the Name column for User ID 113 is returned, as shown in Figure 6.

You can also use this same methodology to navigate between tables. For example, you could do the following to return documents for a specific User ID:

http://localhost:51176/TechBioDataService.svc/Users(113)/Docs

Figure 4. Viewing All Users

Figure 5. Viewing a Specific User

Figure 6. Viewing the Name of a Specific Users

While this information isn't critical to connect to SQL Azure it's good information to have so you know how REST services work and can benefit from its functionality in your application. While this article did not go deep into the Entity Framework or REST technology, there are plenty of good books by APress or information on MSDN about this technology. I highly recommend that you explore these technologies further to enhance your SQL Azure applications.