# 示例：使用低级 适用于 .NET 的 AWS SDK API 进行批处理操作
<a name="batch-operation-lowlevel-dotnet"></a>

**Topics**
+ [示例：使用 适用于 .NET 的 AWS SDK 低级 API 的批处理写入操作](#batch-write-low-level-dotnet)
+ [示例：使用 适用于 .NET 的 AWS SDK 低级 API 的批处理获取操作](#LowLevelDotNetBatchGet)

本节提供 Amazon DynamoDB 支持的批量操作示例，*批处理写入*和*批处理获取*。

## 示例：使用 适用于 .NET 的 AWS SDK 低级 API 的批处理写入操作
<a name="batch-write-low-level-dotnet"></a>

以下 C\$1 代码示例使用 `BatchWriteItem` 方法执行以下放置和删除操作：
+ 在 `Forum` 表中放置一个项目。
+ 在 `Thread` 表中放置一个项目并删除一个项目。

在创建批量写入请求时，您可以就一个或多个表指定任意数量的放置和删除请求。但是，DynamoDB `BatchWriteItem` 对批量写入请求的大小，以及单个批量写入操作中的放置和删除操作数量有限制。有关更多信息，请参阅 [BatchWriteItem](https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_BatchWriteItem.html)。如果您的请求超出这些限制，请求会遭到拒绝。如果您的表的预置吞吐量不足，无法处理此请求，那么响应将返回未处理的请求项目。

以下示例查看响应，了解响应是否包含任何未处理的请求项目。如果存在，则循环返回，并重新发送包含请求中的未处理项目的 `BatchWriteItem` 请求。您还能够以编程方式创建这些表和上传示例数据。有关更多信息，请参阅 [创建示例表并使用 适用于 .NET 的 AWS SDK 上传数据](AppendixSampleDataCodeDotNET.md)。

有关测试以下示例的分步说明，请参阅 [.NET 代码示例](CodeSamples.DotNet.md)。

**Example**  

```
using System;
using System.Collections.Generic;
using Amazon.DynamoDBv2;
using Amazon.DynamoDBv2.Model;
using Amazon.Runtime;

namespace com.amazonaws.codesamples
{
    class LowLevelBatchWrite
    {
        private static string table1Name = "Forum";
        private static string table2Name = "Thread";
        private static AmazonDynamoDBClient client = new AmazonDynamoDBClient();

        static void Main(string[] args)
        {
            try
            {
                TestBatchWrite();
            }
            catch (AmazonServiceException e) { Console.WriteLine(e.Message); }
            catch (Exception e) { Console.WriteLine(e.Message); }

            Console.WriteLine("To continue, press Enter");
            Console.ReadLine();
        }

        private static void TestBatchWrite()
        {
            var request = new BatchWriteItemRequest
            {
                ReturnConsumedCapacity = "TOTAL",
                RequestItems = new Dictionary<string, List<WriteRequest>>
            {
                {
                    table1Name, new List<WriteRequest>
                    {
                        new WriteRequest
                        {
                            PutRequest = new PutRequest
                            {
                                Item = new Dictionary<string, AttributeValue>
                                {
                                    { "Name", new AttributeValue {
                                          S = "S3 forum"
                                      } },
                                    { "Threads", new AttributeValue {
                                          N = "0"
                                      }}
                                }
                            }
                        }
                    }
                },
                {
                    table2Name, new List<WriteRequest>
                    {
                        new WriteRequest
                        {
                            PutRequest = new PutRequest
                            {
                                Item = new Dictionary<string, AttributeValue>
                                {
                                    { "ForumName", new AttributeValue {
                                          S = "S3 forum"
                                      } },
                                    { "Subject", new AttributeValue {
                                          S = "My sample question"
                                      } },
                                    { "Message", new AttributeValue {
                                          S = "Message Text."
                                      } },
                                    { "KeywordTags", new AttributeValue {
                                          SS = new List<string> { "S3", "Bucket" }
                                      } }
                                }
                            }
                        },
                        new WriteRequest
                        {
                            // For the operation to delete an item, if you provide a primary key value
                            // that does not exist in the table, there is no error, it is just a no-op.
                            DeleteRequest = new DeleteRequest
                            {
                                Key = new Dictionary<string, AttributeValue>()
                                {
                                    { "ForumName",  new AttributeValue {
                                          S = "Some partition key value"
                                      } },
                                    { "Subject", new AttributeValue {
                                          S = "Some sort key value"
                                      } }
                                }
                            }
                        }
                    }
                }
            }
            };

            CallBatchWriteTillCompletion(request);
        }

        private static void CallBatchWriteTillCompletion(BatchWriteItemRequest request)
        {
            BatchWriteItemResponse response;

            int callCount = 0;
            do
            {
                Console.WriteLine("Making request");
                response = client.BatchWriteItem(request);
                callCount++;

                // Check the response.

                var tableConsumedCapacities = response.ConsumedCapacity;
                var unprocessed = response.UnprocessedItems;

                Console.WriteLine("Per-table consumed capacity");
                foreach (var tableConsumedCapacity in tableConsumedCapacities)
                {
                    Console.WriteLine("{0} - {1}", tableConsumedCapacity.TableName, tableConsumedCapacity.CapacityUnits);
                }

                Console.WriteLine("Unprocessed");
                foreach (var unp in unprocessed)
                {
                    Console.WriteLine("{0} - {1}", unp.Key, unp.Value.Count);
                }
                Console.WriteLine();

                // For the next iteration, the request will have unprocessed items.
                request.RequestItems = unprocessed;
            } while (response.UnprocessedItems.Count > 0);

            Console.WriteLine("Total # of batch write API calls made: {0}", callCount);
        }
    }
}
```

## 示例：使用 适用于 .NET 的 AWS SDK 低级 API 的批处理获取操作
<a name="LowLevelDotNetBatchGet"></a>

以下 Java 代码示例使用 `BatchGetItem` 方法检索 Amazon DynamoDB 中的 `Forum` 和 `Thread` 表中的多个项目。`BatchGetItemRequest` 指定表名称和每个表的主键列表。示例介绍通过打印检索到的项目来处理响应。

有关测试以下示例的分步说明，请参阅 [.NET 代码示例](CodeSamples.DotNet.md)。

**Example**  

```
using System;
using System.Collections.Generic;
using Amazon.DynamoDBv2;
using Amazon.DynamoDBv2.Model;
using Amazon.Runtime;

namespace com.amazonaws.codesamples
{
    class LowLevelBatchGet
    {
        private static string table1Name = "Forum";
        private static string table2Name = "Thread";
        private static AmazonDynamoDBClient client = new AmazonDynamoDBClient();

        static void Main(string[] args)
        {
            try
            {
                RetrieveMultipleItemsBatchGet();

                Console.WriteLine("To continue, press Enter");
                Console.ReadLine();
            }
            catch (AmazonServiceException e) { Console.WriteLine(e.Message); }
            catch (Exception e) { Console.WriteLine(e.Message); }
        }

        private static void RetrieveMultipleItemsBatchGet()
        {
            var request = new BatchGetItemRequest
            {
                RequestItems = new Dictionary<string, KeysAndAttributes>()
            {
                { table1Name,
                  new KeysAndAttributes
                  {
                      Keys = new List<Dictionary<string, AttributeValue> >()
                      {
                          new Dictionary<string, AttributeValue>()
                          {
                              { "Name", new AttributeValue {
                            S = "Amazon DynamoDB"
                        } }
                          },
                          new Dictionary<string, AttributeValue>()
                          {
                              { "Name", new AttributeValue {
                            S = "Amazon S3"
                        } }
                          }
                      }
                  }},
                {
                    table2Name,
                    new KeysAndAttributes
                    {
                        Keys = new List<Dictionary<string, AttributeValue> >()
                        {
                            new Dictionary<string, AttributeValue>()
                            {
                                { "ForumName", new AttributeValue {
                                      S = "Amazon DynamoDB"
                                  } },
                                { "Subject", new AttributeValue {
                                      S = "DynamoDB Thread 1"
                                  } }
                            },
                            new Dictionary<string, AttributeValue>()
                            {
                                { "ForumName", new AttributeValue {
                                      S = "Amazon DynamoDB"
                                  } },
                                { "Subject", new AttributeValue {
                                      S = "DynamoDB Thread 2"
                                  } }
                            },
                            new Dictionary<string, AttributeValue>()
                            {
                                { "ForumName", new AttributeValue {
                                      S = "Amazon S3"
                                  } },
                                { "Subject", new AttributeValue {
                                      S = "S3 Thread 1"
                                  } }
                            }
                        }
                    }
                }
            }
            };

            BatchGetItemResponse response;
            do
            {
                Console.WriteLine("Making request");
                response = client.BatchGetItem(request);

                // Check the response.
                var responses = response.Responses; // Attribute list in the response.

                foreach (var tableResponse in responses)
                {
                    var tableResults = tableResponse.Value;
                    Console.WriteLine("Items retrieved from table {0}", tableResponse.Key);
                    foreach (var item1 in tableResults)
                    {
                        PrintItem(item1);
                    }
                }

                // Any unprocessed keys? could happen if you exceed ProvisionedThroughput or some other error.
                Dictionary<string, KeysAndAttributes> unprocessedKeys = response.UnprocessedKeys;
                foreach (var unprocessedTableKeys in unprocessedKeys)
                {
                    // Print table name.
                    Console.WriteLine(unprocessedTableKeys.Key);
                    // Print unprocessed primary keys.
                    foreach (var key in unprocessedTableKeys.Value.Keys)
                    {
                        PrintItem(key);
                    }
                }

                request.RequestItems = unprocessedKeys;
            } while (response.UnprocessedKeys.Count > 0);
        }

        private static void PrintItem(Dictionary<string, AttributeValue> attributeList)
        {
            foreach (KeyValuePair<string, AttributeValue> kvp in attributeList)
            {
                string attributeName = kvp.Key;
                AttributeValue value = kvp.Value;

                Console.WriteLine(
                    attributeName + " " +
                    (value.S == null ? "" : "S=[" + value.S + "]") +
                    (value.N == null ? "" : "N=[" + value.N + "]") +
                    (value.SS == null ? "" : "SS=[" + string.Join(",", value.SS.ToArray()) + "]") +
                    (value.NS == null ? "" : "NS=[" + string.Join(",", value.NS.ToArray()) + "]")
                    );
            }
            Console.WriteLine("************************************************");
        }
    }
}
```