Amazon DynamoDB
开发人员指南 (API Version 2012-08-10)
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示例:在使用适用于 .NET 的 AWS 开发工具包对象持久化模型的 DynamoDB 中执行查询和扫描

本节中的 C# 示例定义以下类,并将这些类映射到 DynamoDB 中的表。有关创建在此示例中使用的表的更多信息,请参阅创建表并加载示例数据

  • Book 类映射到 ProductCatalog 表

  • ForumThreadReply 类映射到同名的表。

然后,该示例使用 DynamoDBContext 执行以下查询和扫描操作。

  • 按 Id 获取图书。

    ProductCatalog 表的 Id 是其主键,其中不包含排序键。因此,您无法查询此表。您可以使用其 Id 值获取项目。

  • 对 Reply 表执行以下查询 (Reply 表的主键由 Id 属性和 ReplyDateTime 属性构成,ReplyDateTime 为排序键。因此您可以查询此表)。

    • 查找过去 15 天内发布的论坛话题的回复。

    • 查找特定日期范围内发布的论坛话题回复。

  • 扫描 ProductCatalog 表,查找价格低于 0 的图书。

    出于性能考虑,您应使用查询操作 (而非扫描操作)。但是,有时您可能需要扫描表。假如存在数据输入错误,其中一个图书的价格低于 0。此示例扫描 ProductCategory 表查找价格低于 0 的图书项目 (ProductCategory 为图书表)。

有关创建使用实例的说明,请参阅.NET 代码示例

注意

以下示例不适用于 .NET Core,因为它不支持同步方法。有关更多信息,请参阅适用于 .NET 的 AWS 异步 API

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using System; using System.Collections.Generic; using System.Configuration; using Amazon.DynamoDBv2; using Amazon.DynamoDBv2.DataModel; using Amazon.DynamoDBv2.DocumentModel; using Amazon.Runtime; namespace com.amazonaws.codesamples { class HighLevelQueryAndScan { private static AmazonDynamoDBClient client = new AmazonDynamoDBClient(); static void Main(string[] args) { try { DynamoDBContext context = new DynamoDBContext(client); // Get item. GetBook(context, 101); // Sample forum and thread to test queries. string forumName = "Amazon DynamoDB"; string threadSubject = "DynamoDB Thread 1"; // Sample queries. FindRepliesInLast15Days(context, forumName, threadSubject); FindRepliesPostedWithinTimePeriod(context, forumName, threadSubject); // Scan table. FindProductsPricedLessThanZero(context); 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); } } private static void GetBook(DynamoDBContext context, int productId) { Book bookItem = context.Load<Book>(productId); Console.WriteLine("\nGetBook: Printing result....."); Console.WriteLine("Title: {0} \n No.Of threads:{1} \n No. of messages: {2}", bookItem.Title, bookItem.ISBN, bookItem.PageCount); } private static void FindRepliesInLast15Days(DynamoDBContext context, string forumName, string threadSubject) { string replyId = forumName + "#" + threadSubject; DateTime twoWeeksAgoDate = DateTime.UtcNow - TimeSpan.FromDays(15); IEnumerable<Reply> latestReplies = context.Query<Reply>(replyId, QueryOperator.GreaterThan, twoWeeksAgoDate); Console.WriteLine("\nFindRepliesInLast15Days: Printing result....."); foreach (Reply r in latestReplies) Console.WriteLine("{0}\t{1}\t{2}\t{3}", r.Id, r.PostedBy, r.Message, r.ReplyDateTime); } private static void FindRepliesPostedWithinTimePeriod(DynamoDBContext context, string forumName, string threadSubject) { string forumId = forumName + "#" + threadSubject; Console.WriteLine("\nFindRepliesPostedWithinTimePeriod: Printing result....."); DateTime startDate = DateTime.UtcNow - TimeSpan.FromDays(30); DateTime endDate = DateTime.UtcNow - TimeSpan.FromDays(1); IEnumerable<Reply> repliesInAPeriod = context.Query<Reply>(forumId, QueryOperator.Between, startDate, endDate); foreach (Reply r in repliesInAPeriod) Console.WriteLine("{0}\t{1}\t{2}\t{3}", r.Id, r.PostedBy, r.Message, r.ReplyDateTime); } private static void FindProductsPricedLessThanZero(DynamoDBContext context) { int price = 0; IEnumerable<Book> itemsWithWrongPrice = context.Scan<Book>( new ScanCondition("Price", ScanOperator.LessThan, price), new ScanCondition("ProductCategory", ScanOperator.Equal, "Book") ); Console.WriteLine("\nFindProductsPricedLessThanZero: Printing result....."); foreach (Book r in itemsWithWrongPrice) Console.WriteLine("{0}\t{1}\t{2}\t{3}", r.Id, r.Title, r.Price, r.ISBN); } } [DynamoDBTable("Reply")] public class Reply { [DynamoDBHashKey] //Partition key public string Id { get; set; } [DynamoDBRangeKey] //Sort key public DateTime ReplyDateTime { get; set; } // Properties included implicitly. public string Message { get; set; } // Explicit property mapping with object persistence model attributes. [DynamoDBProperty("LastPostedBy")] public string PostedBy { get; set; } // Property to store version number for optimistic locking. [DynamoDBVersion] public int? Version { get; set; } } [DynamoDBTable("Thread")] public class Thread { // PK mapping. [DynamoDBHashKey] //Partition key public string ForumName { get; set; } [DynamoDBRangeKey] //Sort key public DateTime Subject { get; set; } // Implicit mapping. public string Message { get; set; } public string LastPostedBy { get; set; } public int Views { get; set; } public int Replies { get; set; } public bool Answered { get; set; } public DateTime LastPostedDateTime { get; set; } // Explicit mapping (property and table attribute names are different. [DynamoDBProperty("Tags")] public List<string> KeywordTags { get; set; } // Property to store version number for optimistic locking. [DynamoDBVersion] public int? Version { get; set; } } [DynamoDBTable("Forum")] public class Forum { [DynamoDBHashKey] public string Name { get; set; } // All the following properties are explicitly mapped, // only to show how to provide mapping. [DynamoDBProperty] public int Threads { get; set; } [DynamoDBProperty] public int Views { get; set; } [DynamoDBProperty] public string LastPostBy { get; set; } [DynamoDBProperty] public DateTime LastPostDateTime { get; set; } [DynamoDBProperty] public int Messages { get; set; } } [DynamoDBTable("ProductCatalog")] public class Book { [DynamoDBHashKey] //Partition key public int Id { get; set; } public string Title { get; set; } public string ISBN { get; set; } public int Price { get; set; } public string PageCount { get; set; } public string ProductCategory { get; set; } public bool InPublication { get; set; } } }