步骤 2：使用低级别 API 创建表
适用于 .NET 的 AWS 开发工具包 中的文档模型未提供用于创建表的 API，因此您必须使用低级 API。有关更多信息，请参阅处理表：.NET。
在 Microsoft .NET 和 DynamoDB 教程的本步骤中，您将在 Amazon DynamoDB 中创建一个名为 Movies 的表。表的主键由以下属性组成：
-
year– 分区键。AttributeType为N，表示数字。注意
由于“year”是 DynamoDB 中的保留字，当在低级别表达式中引用“year”时，您需要使用
ExpressionAttributeNames对象为它创建一个别名（如#yr）。 -
title– 排序键。AttributeType为S，表示字符串。
DynamoDB_intro 中的 Main 函数通过等待在 02_CreatingTable.cs 文件中实施的异步 CreatingTable_async 函数来执行此操作：
using System; using System.Collections.Generic; using System.Threading.Tasks; using Amazon.DynamoDBv2.Model; namespace DynamoDB_intro { public static partial class Ddb_Intro { /*-------------------------------------------------------------------------- * CreatingTable_async *--------------------------------------------------------------------------*/ public static async Task CreatingTable_async( string new_table_name, List<AttributeDefinition> table_attributes, List<KeySchemaElement> table_key_schema, ProvisionedThroughput provisionedThroughput ) { Console.WriteLine( " -- Creating a new table named {0}...", new_table_name ); if( await checkingTableExistence_async( new_table_name ) ) { Console.WriteLine( " -- No need to create a new table..." ); return; } if( operationFailed ) return; operationSucceeded = false; Task<bool> newTbl = CreateNewTable_async( new_table_name, table_attributes, table_key_schema, provisionedThroughput ); await newTbl; } /*-------------------------------------------------------------------------- * checkingTableExistence_async *--------------------------------------------------------------------------*/ static async Task<bool> checkingTableExistence_async( string tblNm ) { DescribeTableResponse descResponse; operationSucceeded = false; operationFailed = false; ListTablesResponse tblResponse = await Ddb_Intro.client.ListTablesAsync(); if (tblResponse.TableNames.Contains(tblNm)) { Console.WriteLine(" A table named {0} already exists in DynamoDB!", tblNm); // If the table exists, get its description try { descResponse = await Ddb_Intro.client.DescribeTableAsync(Ddb_Intro.movies_table_name); operationSucceeded = true; } catch (Exception ex) { Console.WriteLine(" However, its description is not available ({0})", ex.Message); Ddb_Intro.moviesTableDescription = null; operationFailed = true; return ( true ); } Ddb_Intro.moviesTableDescription = descResponse.Table; return ( true ); } return ( false ); } /*-------------------------------------------------------------------------- * CreateNewTable_async *--------------------------------------------------------------------------*/ public static async Task<bool> CreateNewTable_async( string table_name, List<AttributeDefinition> table_attributes, List<KeySchemaElement> table_key_schema, ProvisionedThroughput provisioned_throughput ) { CreateTableRequest request; CreateTableResponse response; // Build the 'CreateTableRequest' structure for the new table request = new CreateTableRequest { TableName = table_name, AttributeDefinitions = table_attributes, KeySchema = table_key_schema, // Provisioned-throughput settings are always required, // although the local test version of DynamoDB ignores them. ProvisionedThroughput = provisioned_throughput }; operationSucceeded = false; operationFailed = false; try { Task<CreateTableResponse> makeTbl = Ddb_Intro.client.CreateTableAsync( request ); response = await makeTbl; Console.WriteLine( " -- Created the \"{0}\" table successfully!", table_name ); operationSucceeded = true; } catch( Exception ex ) { Console.WriteLine( " FAILED to create the new table, because: {0}.", ex.Message ); operationFailed = true; return( false ); } // Report the status of the new table... Console.WriteLine( " Status of the new table: '{0}'.", response.TableDescription.TableStatus ); Ddb_Intro.moviesTableDescription = response.TableDescription; return ( true ); } } }
CreatingTable_async 函数首先等待异步 checkingTableExistence_async 函数确定名为“Movies”的表是否已存在。如果该表存在，则 checkingTableExistence_async 会检索现有 Table 的 TableDescription。
如果该表尚不存在，CreatingTable_async 将等待 CreateNewTable_async 使用 DynamoDB 客户端 API CreateTableAsync 创建 Movies。
DynamoDB_intro 示例将尽可能使用异步方法而不是同步方法。这是因为 .NET 内核仅支持异步方式，并且在性能很重要的情况下，异步模式通常是首选。有关更多信息，请参阅适用于 .NET 的 AWS 异步 API。
要了解有关管理表的更多信息，请参阅在 DynamoDB 中使用表。