Published: 31 May 2007
By: Granville Barnett

This article will explain Astoria data web services and their impact upon RIA development as well as including a few examples of using Astoria with ASP.NET AJAX.

Introduction

After reading the title of this article you were probably brought here by curiosity “what is Astoria?” Astoria is a new technology from Microsoft that builds on an established technology Windows Communication Foundation (WCF) and a soon to be de facto data access layer (DAL) technology called Entity Data Model (EDM) which is due for release some time after the Orcas line of products.

Astoria got released at Mix ’07 in the form of a Community Technology Preview (CTP); this is the first chance that we have had to look at Astoria.

Put simply Astoria uses familiar standards based mechanisms to access conceptual data defined in an EDM. We do this by using standard HTTP verbs like GET, POST, PUT, etc.

So why the fuss? Astoria is something that rich internet applications (RIA’s) can really take advantage of. By firing off asynchronous requests to a server using a uniform resource identifier (URI) from your chose technology you can really take advantage of Astoria web data services.

I must admit Astoria is one of those technologies that genuinely get’ me excited – anyone who has built an ASP.NET AJAX application and has fired requests off to web service methods which are fairly static in their composition will really like this technology.

Creating an Astoria Data Service

I mentioned earlier that Astoria is built on two technologies namely WCF, and EDM. It should come as no surprise then that we need to create each – but we do have some aid provided in the form of new item templates in Visual Studio Orcas Beta 1.

Note: Although the EDM wizard comes with Visual Studio Orcas Beta 1, the Astoria CTP does not and you will have to download this from the Microsoft downloads site.

My intention is to not make this a tutorial but rather an informal chat about Astoria and as such I will talk lightly about the steps involved in creating an Astoria data service but I will not go into the explicit steps required.

First thing is first, we need to create an EDM model for our database I have chosen to use the popular Northwind database. This EDM will be used when creating our Astoria data service.

The second step to getting an Astoria data service up and running is to actually add a “Web Data Service” item to your web application project.

Figure 1-1: Adding a Web Data Service to your application

Adding a Web Data Service to your 

application

With the web data service added you need to go into the code behind for that service and derive from the XxxEntities type which the EDM wizard generated for you.

Note: The XxxEntities type is defined in a namespace XxxModel where Xxx in each case is normally the name of the target database, e.g. the Northwind namespace generated is NorthwindModel.

I decided to host my Astoria services using IIS 7 however you can do this using IIS 6, but I haven’t tested it.

When you browse to your service you will see a container XML element called XxxEntities which contains all the entity children that the EDM wizard generated for us. Each entity maps 1..1 with physical tables in your database unless you chose to customize the mappings.

Note: The service endpoint has a file extension of .svc to indicate it is a WCF service.

Figure 1-2: Viewing the service endpoint

Viewing the service endpoint

You can see that in Figure 1-2 I have several entities available to me from my Astoria web data service - Suppliers, Products, Orders, etc...

Consuming the service using the Microsoft AJAX Library

In this article I am going to use ASP.NET AJAX to query the Astoria web data service, you can however use pretty much any technology – I myself have used ASP.NET AJAX, several windows applications as well as WPF (and it’s binding syntax) to use Astoria, each with minimal noise.

Just before we see some code I would like to point out that ASP.NET Futures does provide support for consuming Astoria web data services – I have chosen not to use this however to reach a wider audience, after all everyone is still learning ASP.NET AJAX 1.0! The API introduced into ASP.NET Futures really isn’t that much of a big deal; it just removes a few steps that are a little “dirty” as you will see in the following code.

With ASP.NET AJAX we are familiar with sending some async request to a web server and receiving some data back – this is a paradigm established with AJAX applications where we separate the presentation, behaviour and data. Commonly the presentation is HTML, the behaviour is JavaScript which communicates with the server on the clients behalf and the data is served up in either XML or JSON.

Astoria web data services support three types of data exchange format including:

  1. XML
  2. JSON
  3. RDF+XML

For this article we will, of course, be using JSON. Using JSON allows us to interact with objects after eval’ing the JSON string passed to us from the server.

I think for the first query let’s just go ahead and retrieve all of the customers.

Listing 1-1: Retrieving all of the customers

Note: There is a class that comes with the Astoria samples that provides a class and series of methods to create a more encapsulated approach to calling an Astoria web data service.

Figure 1-3: Running Listing 1-1.

Running Listing 1-1

It’s not my intention to go through the various filtering syntax in this article or all of the features provided by Astoria web data services like adding, updating and deleting data.

Before I wrap this up let’s take a lot at some queries where we use the URI to further filter the results.

Listing 1-2: Ordering the results by ContactName

Listing 1-3: Selecting the top 10 results from Listing 1-2.

Summary

Astoria is set to provide RIA developers with a richer way of interacting with data on the server. The syntax is easy and there is a more structure API on the way for ASP.NET AJAX in ASP.NET Futures (the Mix.DataService JavaScript namespace is included with the Astoria CTP samples). Go and download the CTP bits and give it a go!

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About Granville Barnett

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This author has published 32 articles on DotNetSlackers. View other articles or the complete profile here.

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Discussion


Subject Author Date
placeholder Good Post Suresh Kumar 6/14/2007 7:26 AM
But wait...you can lock your EDM down Granville Barnett 6/14/2007 10:19 AM
placeholder You should look at SnapLogic... Chris Marino 8/2/2007 11:22 PM

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