示例：使用 AWS SDK for .NET 文档模型的 CRUD 操作

下面的 C# 代码示例执行以下操作：

• 在 ProductCatalog 表中创建图书项目。

• 检索图书项目。

• 更新图书项目。该代码示例显示添加新属性和更新现有属性的普通更新。同时还显示仅当现有价格值与代码中指定的值一致时才更新图书价格的有条件更新。

• 删除图书项目。

有关测试以下示例的 step-by-step 说明，请参阅.NET 代码示例。

例

using System;
using System.Collections.Generic;
using System.Linq;
using Amazon.DynamoDBv2;
using Amazon.DynamoDBv2.DocumentModel;
using Amazon.Runtime;

namespace com.amazonaws.codesamples
{
    class MidlevelItemCRUD
    {
        private static AmazonDynamoDBClient client = new AmazonDynamoDBClient();
        private static string tableName = "ProductCatalog";
        // The sample uses the following id PK value to add book item.
        private static int sampleBookId = 555;

        static void Main(string[] args)
        {
            try
            {
                Table productCatalog = Table.LoadTable(client, tableName);
                CreateBookItem(productCatalog);
                RetrieveBook(productCatalog);
                // Couple of sample updates.
                UpdateMultipleAttributes(productCatalog);
                UpdateBookPriceConditionally(productCatalog);

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

        // Creates a sample book item.
        private static void CreateBookItem(Table productCatalog)
        {
            Console.WriteLine("\n*** Executing CreateBookItem() ***");
            var book = new Document();
            book["Id"] = sampleBookId;
            book["Title"] = "Book " + sampleBookId;
            book["Price"] = 19.99;
            book["ISBN"] = "111-1111111111";
            book["Authors"] = new List<string> { "Author 1", "Author 2", "Author 3" };
            book["PageCount"] = 500;
            book["Dimensions"] = "8.5x11x.5";
            book["InPublication"] = new DynamoDBBool(true);
            book["InStock"] = new DynamoDBBool(false);
            book["QuantityOnHand"] = 0;

            productCatalog.PutItem(book);
        }

        private static void RetrieveBook(Table productCatalog)
        {
            Console.WriteLine("\n*** Executing RetrieveBook() ***");
            // Optional configuration.
            GetItemOperationConfig config = new GetItemOperationConfig
            {
                AttributesToGet = new List<string> { "Id", "ISBN", "Title", "Authors", "Price" },
                ConsistentRead = true
            };
            Document document = productCatalog.GetItem(sampleBookId, config);
            Console.WriteLine("RetrieveBook: Printing book retrieved...");
            PrintDocument(document);
        }

        private static void UpdateMultipleAttributes(Table productCatalog)
        {
            Console.WriteLine("\n*** Executing UpdateMultipleAttributes() ***");
            Console.WriteLine("\nUpdating multiple attributes....");
            int partitionKey = sampleBookId;

            var book = new Document();
            book["Id"] = partitionKey;
            // List of attribute updates.
            // The following replaces the existing authors list.
            book["Authors"] = new List<string> { "Author x", "Author y" };
            book["newAttribute"] = "New Value";
            book["ISBN"] = null; // Remove it.

            // Optional parameters.
            UpdateItemOperationConfig config = new UpdateItemOperationConfig
            {
                // Get updated item in response.
                ReturnValues = ReturnValues.AllNewAttributes
            };
            Document updatedBook = productCatalog.UpdateItem(book, config);
            Console.WriteLine("UpdateMultipleAttributes: Printing item after updates ...");
            PrintDocument(updatedBook);
        }

        private static void UpdateBookPriceConditionally(Table productCatalog)
        {
            Console.WriteLine("\n*** Executing UpdateBookPriceConditionally() ***");

            int partitionKey = sampleBookId;

            var book = new Document();
            book["Id"] = partitionKey;
            book["Price"] = 29.99;

            // For conditional price update, creating a condition expression.
            Expression expr = new Expression();
            expr.ExpressionStatement = "Price = :val";
            expr.ExpressionAttributeValues[":val"] = 19.00;

            // Optional parameters.
            UpdateItemOperationConfig config = new UpdateItemOperationConfig
            {
                ConditionalExpression = expr,
                ReturnValues = ReturnValues.AllNewAttributes
            };
            Document updatedBook = productCatalog.UpdateItem(book, config);
            Console.WriteLine("UpdateBookPriceConditionally: Printing item whose price was conditionally updated");
            PrintDocument(updatedBook);
        }

        private static void DeleteBook(Table productCatalog)
        {
            Console.WriteLine("\n*** Executing DeleteBook() ***");
            // Optional configuration.
            DeleteItemOperationConfig config = new DeleteItemOperationConfig
            {
                // Return the deleted item.
                ReturnValues = ReturnValues.AllOldAttributes
            };
            Document document = productCatalog.DeleteItem(sampleBookId, config);
            Console.WriteLine("DeleteBook: Printing deleted just deleted...");
            PrintDocument(document);
        }

        private static void PrintDocument(Document updatedDocument)
        {
            foreach (var attribute in updatedDocument.GetAttributeNames())
            {
                string stringValue = null;
                var value = updatedDocument[attribute];
                if (value is Primitive)
                    stringValue = value.AsPrimitive().Value.ToString();
                else if (value is PrimitiveList)
                    stringValue = string.Join(",", (from primitive
                                    in value.AsPrimitiveList().Entries
                                                    select primitive.Value).ToArray());
                Console.WriteLine("{0} - {1}", attribute, stringValue);
            }
        }
    }
}