範例：在 DynamoDB 支援中查詢和掃描 AWS SDK for .NET 對象持久性模型

本節中的 C# 範例定義下列類別，並將它們映射至 DynamoDB 中的資料表。如需建立在此範例中所使用的資料表之詳細資訊，請參閱 在 DynamoDB 中建立資料表，以及載入程式碼範例的資料。

• Book 類別會映射至 ProductCatalog 資料表。

• Forum、Thread 與 Reply 類別映射至同名的資料表。

範例接著會使用 DynamoDBContext 來執行下列查詢和掃描操作。

• 依 Id 取得書籍。

  ProductCatalog 資料表有 Id 作為其主索引鍵。它沒有排序索引鍵做為其主索引鍵的一部分。因此，您無法查詢資料表。您可以使用項目的 Id 值來取得項目。

• 針對 Reply 資料表執行下列查詢。(Reply 資料表的主索引鍵由 Id 和 ReplyDateTime 屬性組成。ReplyDateTime 是排序索引鍵。因此，您可以查詢此資料表。)

  • 尋找過去 15 天所張貼的論壇主題回覆。

  • 尋找特定日期範圍內所張貼的論壇主題回覆。

• 掃描 ProductCatalog 資料表，尋找價格低於零的書籍。

  基於效能考量，您應該使用查詢操作，而不是掃描操作。不過，您有時可能需要掃描資料表。假設發生資料輸入錯誤，而其中一個書籍價格設定為低於 0。此範例會掃描 ProductCategory 資料表，尋找價格低於 0 的書籍項目 (ProductCategory 為 book)。

如需建立可行範例的說明，請參閱 。 NET程式碼範例。

注意

下列範例不適用於。 NET核心，因為它不支持同步方法。如需詳細資訊，請參閱 AWS 非同步APIs的. NET。

範例

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 an 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
    {
        // Partition key 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
        // 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;
        }
    }
}