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Integrating DataMarket Data with a Visual Web Part : Create a WCF Service to Retrieve DATA.gov Crime Data (part 1)

7/21/2011 4:59:57 PM
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Although being able to manually explore the Windows Azure Marketplace DataMarket data is interesting, it’s arguably a little more interesting to consume that data programmatically from within other applications such as SharePoint Web Parts. Consuming the data in a Web Part involves data aggregation, creating custom filtering options, and of course, making other parts of SharePoint more meaningful through richer data sets.

In this section, you’ll create a WCF service that will retrieve the DATA.gov crime data from the Windows Azure DataMarket data programmatically. The reason for using a WCF service is that you can repurpose the service across different applications, thus mitigating the amount of disparate code you need to manage. (Note that you can also deploy the WCF service to Windows Azure and then use the data for Microsoft Office 365/SharePoint Online applications.) For example, you can build a SharePoint Visual Web Part and a Microsoft Silverlight application; both can use a common WCF service but consume and interact with it in different ways within the Microsoft .NET platform. For example, Silverlight application events must be fired and managed asynchronously.

Here’s the procedure to create a WCF service that retrieves the DATA.gov crime data.

Create a WCF Service to Retrieve DATA.gov Crime Data

1. Create a WCF Service to Retrieve DATA.gov Crime Data
  1. Open Microsoft Visual Studio 2010.

  2. Click Create | New Project | WCF, and select WCF Service Application. Name the project GetDallasData, and then click OK.

  3. After the project has been created, right-click the project in the Solution Explorer, select Add, and then select Class.

  4. Name the new class CrimeData, and add the properties in bold to the newly created class as shown in the following code:

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;

    namespace GetDallasData
    {
    public class CrimeData
    {
    public string City { get; set; }
    public string Year { get; set; }
    public string Population { get; set; }
    public string ViolentCrime { get; set; }
    public string Robbery { get; set; }
    public string PropertyCrime { get; set; }
    public string Burglary { get; set; }
    }
    }

    The preceding code represents the structure of your in-memory data object. The properties will be used to store specific elements of the incoming data stream. Note that you will not use every element or property in the incoming XML stream—you will use only certain parts of the DATA.gov data. That’s why this in-memory object (the class) does not directly map to all the properties that were displayed when you explored the data via the Marketplace DataMarket site.

  5. Right-click the default Service1.svc file in the Solution Explorer, and rename it to DallasCrimeData.svc. Also, rename the IService1.cs interface file to IDallasCrimeData.cs.


    Note:

    Rename the service and service interface references in the Visual Studio project by clicking the reference in code (for example, Service1), and then click the Refactor menu option and select Rename. Provide the new name for the service and service interface.


    Your project folders should now look like the following image.



  6. Double-click the DallasCrimeData.svc file, delete the starter methods that Visual Studio creates for you, and update the code as shown in bold in the following code. This will retrieve the Windows Azure data from the DataMarket by using a WebRequest object. You need to pass your Windows Live ID (for example, john_doe@hotmail.com) and your account key (which looks something like asaaKe8kisiK8leE+JkkswjSv2okwWy3zYAIcsbvC4TT=) with the WebRequest:

    using System;
    using System.Collections.Generic;
    using System.Runtime.Serialization;
    using System.ServiceModel;

    using System.ServiceModel.Web;
    using System.Text;
    using System.Net;
    using System.IO;
    using System.Xml.Linq;
    using System.Linq;

    namespace GetDallasData
    {
    public class DallasCrimeData : IDallasCrimeData
    {
    string myAccountKey = "myliveID@hotmail.com";
    string myUniqueUserId = "your key here";
    string myDallasURL = "https://api.datamarket.azure.com/Data.ashx/data.gov/
    Crimes/CityCrime?$filter=State%20eq%20%27Washington%27&$top=100";
    public List<CrimeData> GetCrimeData(string stateFilter)
    {
    List<CrimeData> listOfCrimesInWashington = new List<CrimeData>();

    WebRequest azureWebRequest = WebRequest.Create(myDallasURL);
    azureWebRequest.Credentials = new NetworkCredential(myAccountKey,
    myUniqueUserId);

    using (HttpWebResponse azureWebResponse = (HttpWebResponse)azureWebRequest.
    GetResponse())
    {
    using (Stream AzureDataStream = azureWebResponse.GetResponseStream())
    {
    using (StreamReader reader = new StreamReader(AzureDataStream))
    {
    string responseFromAzure = reader.ReadToEnd();
    XDocument xmlAzureResultData = XDocument.Parse(responseFrom
    Azure);

    XNamespace nsContent = "http://www.w3.org/2005/Atom";
    XNamespace nsProperties = "http://schemas.microsoft.com/
    ado/2007/08/dataservices/metadata";
    XNamespace nsValue = "http://schemas.microsoft.com/
    ado/2007/08/dataservices";

    var result = (from q in xmlAzureResultData.
    Descendants(nsContent + "entry")
    select new CrimeData
    {
    City = q.Element(nsContent + "content").
    Element(nsProperties + "properties").Element(nsValue + "City").Value.ToString(),
    Year = q.Element(nsContent + "content").
    Element(nsProperties + "properties").Element(nsValue + "Year").Value.ToString(),
    Population = q.Element(nsContent +
    "content").Element(nsProperties + "properties").Element(nsValue +
    "Population").Value.ToString(),
    ViolentCrime = q.Element(nsContent +
    "content").Element(nsProperties + "properties").Element(nsValue +
    "ViolentCrime").Value.ToString(),
    Robbery = q.Element(nsContent + "content").
    Element(nsProperties + "properties").Element(nsValue + "Robbery").Value.ToString(),
    PropertyCrime = q.Element(nsContent +
    "content").Element(nsProperties + "properties").Element(nsValue +
    "PropertyCrime").Value.ToString(),
    Burglary = q.Element(nsContent + "content").
    Element(nsProperties + "properties").Element(nsValue + "Burglary").Value.ToString()
    });
    foreach (var c in result)
    {
    listOfCrimesInWashington.Add(c);
    }
    }
    }
    }
    return listOfCrimesInWashington;
    }
    }
    }


    The purpose of the preceding code is to use a predefined REST URI (one that retrieves crime data for Washington state), as shown here:

    https://api.datamarket.azure.com/Data.ashx/Data.gov/Crimes/CityCrime?$filter=State%20eq%20%27Washington%27&$top=100

    You then manage the data returned from the Marketplace DataMarket by loading it into an XDocument object that is then parsed and read into your custom object. Remember that you’re reading only specific parts of the XDocument object into the in-memory CrimeData object.

  7. After adding the core service operation, you’ll need to add the interface contract. To do this, double-click the IDallasCrimeData.cs file, delete the starter methods, and edit it, adding the bold code as shown below:

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Runtime.Serialization;
    using System.ServiceModel;
    using System.ServiceModel.Web;
    using System.Text;

    namespace GetDallasData
    {
    [ServiceContract]
    public interface IDallasCrimeData
    {
    [OperationContract]
    List<CrimeData> GetCrimeData(string stateFilter);
    }
    }

  8. To test the service, either press F5 on your keyboard or right-click DallasCrimeData.svc in the Solution Explorer and select View In Browser. The result should display a file listing in your browser. If you click your DallasCrimeData.svc file, the resulting page will be similar to the following image.



You have now created the core WCF service that you’ll be able to use to retrieve the Windows Azure data from the Marketplace DataMarket. However, before you can use the service, you’ll want to deploy it somewhere. This requires you to first publish the service from your Visual Studio solution to a virtual directory and then create an Internet Information Services (IIS) website.

In this exercise, you’ll deploy the service to your local IIS. Note that you could also deploy this service to Windows Azure and then call the service from there.

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