Introducing Windows Azure- P11 pps

CHAPTER 1 ■ CREATE CLOUD TABLE STORAGE 23 Close SQL Analysis When creating a test cloud storage table, any active SQL query analysis running against the existing cloud storage table needs to be closed from SQL Management Studio to avoid the failure of data storage creation. Summary As we have learned so far, creating cloud table storage is a straightforward job. Microsoft claims that the Azure framework is a true developer-oriented framework. All the hard work should have been done and encapsulated in the SDK. Your life as a .NET developer is now a lot easier; what remains for you to do is nothing but derive your client classes from the base classes from the SDK and follow the right procedures to build your cloud applications. However, I have not presented how to access cloud table storage yet. That is the task we are going to pursue in the next chapter. C H A P T E R 2 ■ ■ ■ 25 Access Cloud Table Storage To access Azure table storage, we must use Azure web roles, since the worker role cannot connect to or communicate with the outside world directly. A worker role is usually used on batch jobs (see the book's introduction). The Azure SDK provides a set of templates in a client service access library, StorageClient.dll. This chapter has three exercises. In the first section of this chapter we will walk through a process to access cloud storage step by step and see how to use these templates to insert and query data using the cloud table storages. The second exercise focuses on deleting the records from a cloud storage table. The third exercise is an example of how to manipulate data in tables with a relational structure. The cloud storage we are going to use was created in Chapter 1. From these three exercises you will learn the basic skills to deal with cloud table storage. Essentially all cloud tables are addressable using a URI. The cloud table can be accessed by a web request via HTTP. The Azure SDK provides client-side components that implement all the base classes used to access Azure table storage. These components can be found in the bin folder of the SDK. You then need to create classes derived from the base classes defined in the SDK. Accessing a Single Cloud Data Storage Table First, let’s see how to access a single cloud data storage table. Before we drill down into the details let’s create a new WebRole cloud service in Visual Studio by selecting New Project ➤ Visual C# ➤ Cloud Service ➤ Web Cloud Service and name it CloudTableStorageService. ■ Note The code for this example is in the exercise 2-1 bundle from the code download. Visual Studio will automatically generate two projects as a solution package. One project is called CloudTableStorageService, and another one is called CloudTableStorageService WebRole. The first project is a new type of Visual Studio project introduced by the Windows Azure framework. There are two files automatically generated in the CloudTableStorageService project by Visual Studio. One is ServiceConfiguration.cscf, a configuration XML file containing user account information. By default, all the URI addresses generated in this file point to the local development environment with a default account authentication key called AccountSharedKey with a base-64 encoding token key value. When a project is deployed to the remote cloud host in a Microsoft data center, all the values in the configuration need to be changed to point to your account. You will find out how to do this later in this book and get information in more detail about deploying an Azure project to a CHAPTER 2 ■ ACCESS CLOUD TABLE STORAGE 26 remote cloud environment from Chapter 9. Visual Studio also adds a reference to point to the second project. The second project, CloudTableStorageService WebRole, is a regular ASP.NET project with a default web form file defined inside the project. Renamed it AddressTable.aspx. Right-click on the second project we have just created, CloudTableStorageService WebRole, and insert three new folders into that project—CloudTableStorageDataContext, CloudTableStorageDataService, and CloudTableStorageDataEntity. We are going to add and implement more classes in these three folders in the rest of this exercise. ■ Note You can delete the second web role project and create your own regular web application type project and add it back by changing the reference to your own web application project. By design there is only one web application project that can be referenced from an Azure storage service project. 1. As Listing 2-1 shows, create a base class TableContext. This class inherits from TableStorageDataServiceContext. This class is part of the Microsoft.ServiceHosting.Service.dll assembly from the Azure SDK. The constructor of the TableContext class takes StorageAccountInfo as a parameter. The StorageAccountInfo class instance retrieves the configuration (DevelopmentStorage.exe.config, shown in Listing 2-2) from the SDK install directory and reads it at runtime. There is no need to do any more work with this derived class. All necessary jobs and hard tasks have been done from the base class. This makes your life a lot easier since you do not need to know the details of how to hook up to the Azure framework runtime environment. The only thing for you to do is to provide correct authentication information. Listing 2-1. A Cloud Data Object Class Must Inherit from the Base Class TableStorageDataServiceContext abstract public class TableContext : TableStorageDataServiceContext { public string TableName { get; set; } public TableContext(StorageAccountInfo accountInfo) : base(accountInfo) { } } Listing 2-2. The Configuration File DevelopmentStorage.exe.config <developmentStorageConfig> <services> <service name="Blob" url="http://127.0.0.1:10000/"/> <service name="Queue" url="http://127.0.0.1:10001/"/> CHAPTER 2 ■ ACCESS CLOUD TABLE STORAGE 27 <service name="Table" url="http://127.0.0.1:10002/" dbServer="localhost\SQLExpress"/> </services> <accounts> <account name="devstoreaccount1" authKey="<AUTH KEY>" isAdmin="false" contactInfo=""/> </accounts> </developmentStorageConfig> 2. Create another class called DataTableService. This class has two member variables. One is the type of the TableContext class we have just created, and the another member variable is the StorageAccountInfo type. This class is also defined in the Microsoft.ServiceHosting.Service.dll assembly of the Azure SDK. In the body of the constructor of the DataTableService class, add a line of code to instantiate the class StorageAccountInfo and the retrieve the account configuration information from the configuration file DevelopmentStorage.exe.config as shown in Figure 2-1. Figure 2-1 shows the debug information at the breakpoint set at the constructor of the DataTableService class at runtime. The configuration information retrieved by the framework should match the configuration settings. The implementation of the TableContext class is fairly straightforward. This class only implements a query interface to the cloud table AddressTable, as Listing 2-1 and the class diagram in Figure 2-2 show. Figure 2-1. Account information is configured in DevelopmentStorage.exe.config and retrieved at runtime . CloudTableStorageService WebRole. The first project is a new type of Visual Studio project introduced by the Windows Azure framework. There are two files automatically generated in the CloudTableStorageService