Azure Table存储（2）

今天我们继续接上一篇来谈一下Table存储。

以编程方式访问Table存储
获取组件

您可以使用NuGet来获取Microsoft.WindowsAzure.Storage.dll组件。 在Solution Explorer里右键点击你的Project， 然后选择Manage Nuget Packages， 在线搜索 “WindowsAzure.Storage” 然后点击安装Azure存储包和相关包。

Azure SDK .NET版也包含Microsoft.WindowsAzure.Storage.dll， 您可以在.NET k开发者中心拿到。 该组件安装在%Program Files%\Microsoft SDKs\Azure\.NET SDK\<sdk-version>\ref\ 目录下。

名字空间声明
把下面的代码加到你的C#程序的最上面以便于您访问Azure存储：

using Microsoft.WindowsAzure.Storage;using Microsoft.WindowsAzure.Storage.Auth;using Microsoft.WindowsAzure.Storage.Table;

确保您引用Microsoft.WindowsAzure.Storage.dll组件

检索连接字符串
您可以使用CloudStorageAccount 类型来展示您的存储账户信息。 如果您使用Azure项目模板或者您有一个关于Microsoft.WindowsAzure.CloudConfigurationManager名字空间的引用， 您也可以是用CloudConfigurationManager 类型从Azure服务配置表来检索您的存储连接字符串和账户信息。

CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));

如果您的应用没有引用Microsoft.WindowsAzure.CloudConfigurationManager， 并且您的连接字符串存放在web.config或者app.config里， 那您就可以使用ConfigurationManager来获取连接字符串了。 不过您还需要添加一个对于System.Configuration.dll 的引用， 然后再添加一个命名空间的声明。

using System.Configuration;...CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    ConfigurationManager.ConnectionStrings["StorageConnectionString"]); 

创建一个表Table
每个CloudTableClient 对象都可以让您拿到tables和entities的引用对象。 下面的代码新建了一个CloudTableClient 对象然后用它来创建一个Table

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();// Create the table if it doesn't exist.CloudTable table = tableClient.GetTableReference("people");table.CreateIfNotExists();

为Table创建一个entity

Entities使用TableEntity继承出来的一个自定义类来映射C# object. 为table添加一个entity， 需要创建一个类来定义你的entity的属性。 下面的代码使用客户的firstname和lastname作为rowkey和partitionkey来定义了一个entity。

public class CustomerEntity : TableEntity{    public CustomerEntity(string lastName, string firstName)    {        this.PartitionKey = lastName;        this.RowKey = firstName;    }    public CustomerEntity() { }    public string Email { get; set; }    public string PhoneNumber { get; set; }}

Table表与entity相关的操作使用的CloudTable 对象。 这个操作使用的是TableOperation 对象。下面的代码展示的是创建CloudTable 对象和CustomerEntity 对象。

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(   CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();// Create the CloudTable object that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Create a new customer entity.CustomerEntity customer1 = new CustomerEntity("Harp", "Walter");customer1.Email = "[e-mail]";customer1.PhoneNumber = "425-555-0101";// Create the TableOperation that inserts the customer entity.TableOperation insertOperation = TableOperation.Insert(customer1);// Execute the insert operation.table.Execute(insertOperation);

批量添加entities
您可以通过一个写操作来批量天剑entities到一个Table里面。
1. 您可以在一个批量操作里包括更新， 删除和插入
2. 一个批量操作里面最多可以包括100 entities
3. 在一个批量操作的所有entities都必须使用相同的partition key
4. 如果是查询操作， 只能是批量操作里的一个唯一操作。

下面的代码使用了其中的TableBatchOperation Insert方法

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();// Create the CloudTable object that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Create the batch operation.TableBatchOperation batchOperation = new TableBatchOperation();// Create a customer entity and add it to the table.CustomerEntity customer1 = new CustomerEntity("Smith", "Jeff");customer1.Email = "[e-mail]";customer1.PhoneNumber = "425-555-0104";// Create another customer entity and add it to the table.CustomerEntity customer2 = new CustomerEntity("Smith", "Ben");customer2.Email = "[e-mail]";customer2.PhoneNumber = "425-555-0102";// Add both customer entities to the batch insert operation.batchOperation.Insert(customer1);batchOperation.Insert(customer2);// Execute the batch operation.table.ExecuteBatch(batchOperation);

在一个partition里面检索所有的entities
要完成这个操作， 您需要是用TableQuery 对象， 代码如下：

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();// Create the CloudTable object that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Construct the query operation for all customer entities where PartitionKey="Smith".TableQuery<CustomerEntity> query = new TableQuery<CustomerEntity>().Where(TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, "Smith"));// Print the fields for each customer.foreach (CustomerEntity entity in table.ExecuteQuery(query)){    Console.WriteLine("{0}, {1}\t{2}\t{3}", entity.PartitionKey, entity.RowKey,        entity.Email, entity.PhoneNumber);}

在一个partition里面检索一系列的entities
如果您不是要检索所有的entities， 而是只需要其中的一部分， 请参照下面的代码

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();//Create the CloudTable object that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Create the table query.TableQuery<CustomerEntity> rangeQuery = new TableQuery<CustomerEntity>().Where(    TableQuery.CombineFilters(        TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, "Smith"),        TableOperators.And,        TableQuery.GenerateFilterCondition("RowKey", QueryComparisons.LessThan, "E")));// Loop through the results, displaying information about the entity.foreach (CustomerEntity entity in table.ExecuteQuery(rangeQuery)){    Console.WriteLine("{0}, {1}\t{2}\t{3}", entity.PartitionKey, entity.RowKey,        entity.Email, entity.PhoneNumber);}

检索一个单独的entity
您也可以单独检索一个entity， 示例代码如下：

/ Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();// Create the CloudTable object that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Create a retrieve operation that takes a customer entity.TableOperation retrieveOperation = TableOperation.Retrieve<CustomerEntity>("Smith", "Ben");// Execute the retrieve operation.TableResult retrievedResult = table.Execute(retrieveOperation);// Print the phone number of the result.if (retrievedResult.Result != null)   Console.WriteLine(((CustomerEntity)retrievedResult.Result).PhoneNumber);else   Console.WriteLine("The phone number could not be retrieved.");

替换一个entity
为了更新一个entity， 需要先从table服务里面拿到entity对象， 然后修改后保存回table服务。下面的代码实现修改现有客户的电话号码， 使用了Replace方法。

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table clientCloudTableClient tableClient = storageAccount.CreateCloudTableClient();// Create the CloudTable object that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Create a retrieve operation that takes a customer entity.TableOperation retrieveOperation = TableOperation.Retrieve<CustomerEntity>("Smith", "Ben");// Execute the operation.TableResult retrievedResult = table.Execute(retrieveOperation);// Assign the result to a CustomerEntity object.CustomerEntity updateEntity = (CustomerEntity)retrievedResult.Result;if (updateEntity != null){   // Change the phone number.   updateEntity.PhoneNumber = "425-555-0105";   // Create the InsertOrReplace TableOperation   TableOperation updateOperation = TableOperation.Replace(updateEntity);   // Execute the operation.   table.Execute(updateOperation);   Console.WriteLine("Entity updated.");}else   Console.WriteLine("Entity could not be retrieved.");

Insert-or-replace一个entity
如果entity在从server调用后已经被修改过了， 则Replace会失败。 但是有时候你会不知道这个entity是否已经存在或者修改， 那这时候我们就可以使用InsertOrReplace

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();// Create the CloudTable object that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Create a retrieve operation that takes a customer entity.TableOperation retrieveOperation = TableOperation.Retrieve<CustomerEntity>("Smith", "Ben");// Execute the operation.TableResult retrievedResult = table.Execute(retrieveOperation);// Assign the result to a CustomerEntity object.CustomerEntity updateEntity = (CustomerEntity)retrievedResult.Result;if (updateEntity != null){   // Change the phone number.   updateEntity.PhoneNumber = "425-555-1234";   // Create the InsertOrReplace TableOperation   TableOperation insertOrReplaceOperation = TableOperation.InsertOrReplace(updateEntity);   // Execute the operation.   table.Execute(insertOrReplaceOperation);   Console.WriteLine("Entity was updated.");}else   Console.WriteLine("Entity could not be retrieved.");

查询entity属性的子集
示例代码如下：

// Retrieve storage account from connection stringCloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table clientCloudTableClient tableClient = storageAccount.CreateCloudTableClient();//Create the CloudTable that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Define the query, and only select the Email propertyTableQuery<DynamicTableEntity> projectionQuery = new TableQuery<DynamicTableEntity>().Select(new string[] { "Email" });// Define an entity resolver to work with the entity after retrieval.EntityResolver<string> resolver = (pk, rk, ts, props, etag) => props.ContainsKey("Email") ? props["Email"].StringValue : null;foreach (string projectedEmail in table.ExecuteQuery(projectionQuery, resolver, null, null)){    Console.WriteLine(projectedEmail);}

删除一个entity
你可以在接收到一个entity之后轻松的删除它。

// Retrieve storage account from connection stringCloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table clientCloudTableClient tableClient = storageAccount.CreateCloudTableClient();//Create the CloudTable that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Create a retrieve operation that expects a customer entity.TableOperation retrieveOperation = TableOperation.Retrieve<CustomerEntity>("Smith", "Ben");// Execute the operation.TableResult retrievedResult = table.Execute(retrieveOperation);// Assign the result to a CustomerEntity.CustomerEntity deleteEntity = (CustomerEntity)retrievedResult.Result;// Create the Delete TableOperation.if (deleteEntity != null){   TableOperation deleteOperation = TableOperation.Delete(deleteEntity);   // Execute the operation.   table.Execute(deleteOperation);   Console.WriteLine("Entity deleted.");}else   Console.WriteLine("Could not retrieve the entity.");

删除一个Table
示例代码如下

// Retrieve the storage account from the connection string.CloudStorageAccount storageAccount = CloudStorageAccount.Parse(    CloudConfigurationManager.GetSetting("StorageConnectionString"));// Create the table client.CloudTableClient tableClient = storageAccount.CreateCloudTableClient();//Create the CloudTable that represents the "people" table.CloudTable table = tableClient.GetTableReference("people");// Delete the table it if exists.table.DeleteIfExists();

异步方式接收entities
您如果需要读取以大批entities， 而且您想实时得的结果， 那您可以使用异步的方式。 示例代码如下：

// Initialize a default TableQuery to retrieve all the entities in the table
TableQuery tableQuery = new TableQuery();

// Initialize the continuation token to null to start from the beginning of the tableTableContinuationToken continuationToken = null;do{    // Retrieve a segment (up to 1000 entities)    TableQuerySegment<CustomerEntity> tableQueryResult =        await table.ExecuteQuerySegmentedAsync(tableQuery, continuationToken);    // Assign the new continuation token to tell the service where to    // continue on the next iteration (or null if it has reached the end)    continuationToken = tableQueryResult.ContinuationToken;    // Print the number of rows retrieved    Console.WriteLine("Rows retrieved {0}", tableQueryResult.Results.Count);// Loop until a null continuation token is received indicating the end of the table} while(continuationToken != null);