CHAPTER 2 ■ ACCESS CLOUD TABLE STORAGE 43 approach for handling Azure message login. His article can be found at http:// blogs.msdn.com/brunoterkaly/archive/2009/01/18/windows-azure-services-exercise-2- configuration-logging-and-debugging.aspx. Leverage the Power of Development Fabric Services We briefly described the development fabric in the Introduction. The development fabric is a powerful feature of the Azure Framework. The development fabric simulates the Azure fabric service on a local computer environment. You can run, test, debug, and do any necessary tuning on performance or local configuration before deploying applications to production. An Azure application can be deployed to the local fabric and run stand-alone from the local fabric as well as launching from Visual Studio if step-by-step debugging is needed. Azure applications need to be packed before being deployed to either the local fabric or the Azure fabric. The package can be generated using a command-line utility from the SDK, CSPack, with the /copyonly option. CSPack will generate a structured package, including the configuration file. The package will be automatically generated if you select Publish by right-clicking on the solution node of an application from Visual Studio. The generated configuration package and application package can be found from the project folder as shown in Figure 2-10. Figure 2-10. The package used to deploy an Azure application to fabric The command-line utility provided by the Azure SDK, CSRun.exe, is the tool used to deploy the package to the local fabric, which can be found from the installed SDK bin directory. Detailed information to use this tool can be found from MSDN http://msdn.microsoft.com/en-us/library/ dd179412.aspx. Based on my experience, in most cases Visual Studio in conjunction with the Azure Portal should handle all deployment tasks very well. Using Fiddler 2 to Debug Cloud Storage Applications Fiddler 2 is a very powerful web debugging tool from Microsoft and can be downloaded from http://www.fiddler2.com/fiddler2/. This tool can be used to compose, listen to, and send HTTP messages. This tool can also be used to debug and test Azure applications including cloud storage applications. Below is an example of how to use this tool to help debug a cloud storage application. In order to do the demo we need to deploy the cloud storage application we created previously to run from the remote Azure fabric. Deploying an application to the remote Azure cloud environment is a topic covered in Chapter 9. When the application is successfully hosted in the cloud, there is an URL assigned as shown in Figure 2-11. CHAPTER 2 ■ ACCESS CLOUD TABLE STORAGE 44 Figure 2-11. The URL is assigned after the storage web role has been deployed to Microsoft and is running from the remote cloud environment Copy that URL in your browser and Default.aspx will launch the application and access the remote storage as Figure 2-12 shows. Figure 2-13 shows the debugging information captured when we click on the Add button using Microsoft Fiddler 2. Figure 2-12. As the web role been hosted from Microsoft, using the URL as shown from Figure 2-11 to launch the default.aspx page and access the storage running in the cloud CHAPTER 2 ■ ACCESS CLOUD TABLE STORAGE 45 Figure 2-13. The HTTP debugging information captured when adding data to a cloud storage table using Microsoft Fiddler2 Leverage LINQ to Query Entities in Cloud Storage LINQ is a feature introduced with Microsoft .NET 3.0 that provides an agile way to query cloud table entities. Listing 2-13 is an example of using LINQ to print out all RowKey values of all rows from the table Address for tracing purposes. Listing 2-13. Using LINQ to Query RowKey Values of All Rows from Address Table addressTableService.TableContext().CreateQuery<Address> ( addressTableService.TableContext().TableName).ToList<Address>().ForEach( x => System.Diagnostics.Trace.WriteLine(string.Format(" Row Key = <{0}>", x.RowKey))); An example using LINQ to return the top two entities from the Address table is shown in Listing 2-14. Listing 2-14. Using LINQ to Query RowKey Top N Rows from the Address Table int i = 0; foreach( Address a in addressTableService.TableContext() .CreateQuery<Address>( addressTableService.TableContext().TableNam) .ToList<Address>().Take<Address>(2) ) { System.Diagnostics.Trace.WriteLine( CHAPTER 2 ■ ACCESS CLOUD TABLE STORAGE 46 string.Format(" Row Key[{0}] = <{1}>", i, a.RowKey) ); ++i; } Using HTTP REST to Query the Top N Entities REST (Representational State Transfer) provides a powerful way to access Internet resources using HTTP and is widely used for web-related applications. It can also be used to access Azure table storage. The syntax to retrieve the top N entities from a cloud table is the following, using HTTP GET: http://<TableStorageSolution>.table.core.windows.net/<TableName>()?$top=N To query our Address table for the top 10 records the syntax is: http://softnetsolutionstorage.table.core.windows.net/AddressTable()?$top=10 Using Continuation Tokens to Retrieve Paginated Data When querying a large set of data from cloud tables, the number of entities returned in the query may be limited due to one of the following reasons: • The number of total entities to return is greater than the maximum number of entities allowed in the response by the server (currently 1,000). • The total size of the entities in the response is greater than the maximum size of a response, currently 4 MB including the property names but excluding the XML tags used for REST. • The time for completing the query is more than the timeout (currently 60 seconds). If your queries fall foul of these restrictions, you can use continuation tokens to page the data. You can consider continuation tokens to be keys used to query data sequentially, where one chunk of data follows another one. The continuation tokens can be obtained from the return header from the current query results. Listing 2-15 is sample code to peek at continuation tokens. This piece of code is a stand-alone piece and not part of the project of this exercise. We leave it to you as homework. (The class DataServiceQuery used in this piece of code is a class from the StorageClient assembly of the Azure SDK.) The highlighted code in the next listing shows how to get the continuation token programmatically from the response header. There is no continuation token returned if the query does not meet the limit conditions listed above. This function is extracted from the project in the next exercise and can be found from the code in Default.aspx.cs. We are going to talk more about the continuation tokens used in the code in the next section. Listing 2-15. Sample Code for Peeking at the Continuation Tokens private void ContinuationKeyPeek() { AddressTableContext tableContext = CHAPTER 2 ■ ACCESS CLOUD TABLE STORAGE 47 addressTableService.TableContext() as AddressTableContext; ContinuationToken continuationToken = null; do { var topTenAddress = tableContext.CreateQuery<Address>(tableContext.TableName).Take(10); var query = topTenAddress as DataServiceQuery<Address>; if (continuationToken != null) { query = query.AddQueryOption("NextPartitionKey", continuationToken.PartitionKey); if (continuationToken.RowKey != null) { query = query.AddQueryOption("NextRowKey", continuationToken.RowKey); } } var response = query.Execute() as QueryOperationResponse; if (response.Headers.ContainsKey("x-ms-continuation-NextPartitionKey")) { continuationToken.PartitionKey = response.Headers["x-ms-continuation-NextPartitionKey"]; if (response.Headers.ContainsKey("x-ms-continuation-NextRowKey")) { continuationToken.RowKey = response.Headers["x-ms-continuation-NextRowKey"]; } } else { continuationToken = null; } } while (continuationToken != null); } public class ContinuationToken { public string PartitionKey { get; set; } public string RowKey { get; set; } } There are rich technologies available to retrieve the data from cloud table storage, including the web role service offered by the Azure Framework, LINQ or REST, or tools such as Fiddler using the HTTP protocol. Next we are going to learn other basic cloud table storage data I/O actions—deleting and updating data from cloud table storage. . login. His article can be found at http:// blogs.msdn.com/brunoterkaly/archive/2009/01/18 /windows- azure-services-exercise-2- configuration-logging-and-debugging.aspx. Leverage the Power of. http://<TableStorageSolution>.table.core .windows. net/<TableName>()?$top=N To query our Address table for the top 10 records the syntax is: http://softnetsolutionstorage.table.core .windows. net/AddressTable()?$top=10