Amazon DynamoDB
开发人员指南 (API Version 2012-08-10)
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示例:查询和扫描

本节中的 Java 示例定义以下类,并将这些类映射到 DynamoDB 中的表。有关创建示例表的更多信息,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。

该示例然后使用 DynamoDBMapper 实例来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 属性共同构成。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 表查找价格低于指定值的图书。

    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)。

  • 对 ProductCatalog 表执行并行扫描查找特定类型的自行车。

注意

此代码示例假定您已按照 创建表并加载示例数据 部分的说明,为您的账户将数据加载到了 DynamoDB 中。

有关运行以下示例的分步说明,请参阅 Java 代码示例

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// Copyright 2012-2015 Amazon.com, Inc. or its affiliates. All Rights Reserved. // Licensed under the Apache License, Version 2.0. package com.amazonaws.codesamples.datamodeling; import java.text.SimpleDateFormat; import java.util.Date; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Set; import java.util.TimeZone; import com.amazonaws.services.dynamodbv2.AmazonDynamoDB; import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBQueryExpression; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBRangeKey; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBScanExpression; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable; import com.amazonaws.services.dynamodbv2.model.AttributeValue; public class DynamoDBMapperQueryScanExample { static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build(); public static void main(String[] args) throws Exception { try { DynamoDBMapper mapper = new DynamoDBMapper(client); // Get a book - Id=101 GetBook(mapper, 101); // Sample forum and thread to test queries. String forumName = "Amazon DynamoDB"; String threadSubject = "DynamoDB Thread 1"; // Sample queries. FindRepliesInLast15Days(mapper, forumName, threadSubject); FindRepliesPostedWithinTimePeriod(mapper, forumName, threadSubject); // Scan a table and find book items priced less than specified // value. FindBooksPricedLessThanSpecifiedValue(mapper, "20"); // Scan a table with multiple threads and find bicycle items with a // specified bicycle type int numberOfThreads = 16; FindBicyclesOfSpecificTypeWithMultipleThreads(mapper, numberOfThreads, "Road"); System.out.println("Example complete!"); } catch (Throwable t) { System.err.println("Error running the DynamoDBMapperQueryScanExample: " + t); t.printStackTrace(); } } private static void GetBook(DynamoDBMapper mapper, int id) throws Exception { System.out.println("GetBook: Get book Id='101' "); System.out.println("Book table has no sort key. You can do GetItem, but not Query."); Book book = mapper.load(Book.class, 101); System.out.format("Id = %s Title = %s, ISBN = %s %n", book.getId(), book.getTitle(), book.getISBN()); } private static void FindRepliesInLast15Days(DynamoDBMapper mapper, String forumName, String threadSubject) throws Exception { System.out.println("FindRepliesInLast15Days: Replies within last 15 days."); String partitionKey = forumName + "#" + threadSubject; long twoWeeksAgoMilli = (new Date()).getTime() - (15L * 24L * 60L * 60L * 1000L); Date twoWeeksAgo = new Date(); twoWeeksAgo.setTime(twoWeeksAgoMilli); SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"); dateFormatter.setTimeZone(TimeZone.getTimeZone("UTC")); String twoWeeksAgoStr = dateFormatter.format(twoWeeksAgo); Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>(); eav.put(":val1", new AttributeValue().withS(partitionKey)); eav.put(":val2", new AttributeValue().withS(twoWeeksAgoStr.toString())); DynamoDBQueryExpression<Reply> queryExpression = new DynamoDBQueryExpression<Reply>() .withKeyConditionExpression("Id = :val1 and ReplyDateTime > :val2").withExpressionAttributeValues(eav); List<Reply> latestReplies = mapper.query(Reply.class, queryExpression); for (Reply reply : latestReplies) { System.out.format("Id=%s, Message=%s, PostedBy=%s %n, ReplyDateTime=%s %n", reply.getId(), reply.getMessage(), reply.getPostedBy(), reply.getReplyDateTime()); } } private static void FindRepliesPostedWithinTimePeriod(DynamoDBMapper mapper, String forumName, String threadSubject) throws Exception { String partitionKey = forumName + "#" + threadSubject; System.out.println( "FindRepliesPostedWithinTimePeriod: Find replies for thread Message = 'DynamoDB Thread 2' posted within a period."); long startDateMilli = (new Date()).getTime() - (14L * 24L * 60L * 60L * 1000L); // Two // weeks // ago. long endDateMilli = (new Date()).getTime() - (7L * 24L * 60L * 60L * 1000L); // One // week // ago. SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"); dateFormatter.setTimeZone(TimeZone.getTimeZone("UTC")); String startDate = dateFormatter.format(startDateMilli); String endDate = dateFormatter.format(endDateMilli); Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>(); eav.put(":val1", new AttributeValue().withS(partitionKey)); eav.put(":val2", new AttributeValue().withS(startDate)); eav.put(":val3", new AttributeValue().withS(endDate)); DynamoDBQueryExpression<Reply> queryExpression = new DynamoDBQueryExpression<Reply>() .withKeyConditionExpression("Id = :val1 and ReplyDateTime between :val2 and :val3") .withExpressionAttributeValues(eav); List<Reply> betweenReplies = mapper.query(Reply.class, queryExpression); for (Reply reply : betweenReplies) { System.out.format("Id=%s, Message=%s, PostedBy=%s %n, PostedDateTime=%s %n", reply.getId(), reply.getMessage(), reply.getPostedBy(), reply.getReplyDateTime()); } } private static void FindBooksPricedLessThanSpecifiedValue(DynamoDBMapper mapper, String value) throws Exception { System.out.println("FindBooksPricedLessThanSpecifiedValue: Scan ProductCatalog."); Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>(); eav.put(":val1", new AttributeValue().withN(value)); eav.put(":val2", new AttributeValue().withS("Book")); DynamoDBScanExpression scanExpression = new DynamoDBScanExpression() .withFilterExpression("Price < :val1 and ProductCategory = :val2").withExpressionAttributeValues(eav); List<Book> scanResult = mapper.scan(Book.class, scanExpression); for (Book book : scanResult) { System.out.println(book); } } private static void FindBicyclesOfSpecificTypeWithMultipleThreads(DynamoDBMapper mapper, int numberOfThreads, String bicycleType) throws Exception { System.out.println("FindBicyclesOfSpecificTypeWithMultipleThreads: Scan ProductCatalog With Multiple Threads."); Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>(); eav.put(":val1", new AttributeValue().withS("Bicycle")); eav.put(":val2", new AttributeValue().withS(bicycleType)); DynamoDBScanExpression scanExpression = new DynamoDBScanExpression() .withFilterExpression("ProductCategory = :val1 and BicycleType = :val2").withExpressionAttributeValues(eav); List<Bicycle> scanResult = mapper.parallelScan(Bicycle.class, scanExpression, numberOfThreads); for (Bicycle bicycle : scanResult) { System.out.println(bicycle); } } @DynamoDBTable(tableName = "ProductCatalog") public static class Book { private int id; private String title; private String ISBN; private int price; private int pageCount; private String productCategory; private boolean inPublication; @DynamoDBHashKey(attributeName = "Id") public int getId() { return id; } public void setId(int id) { this.id = id; } @DynamoDBAttribute(attributeName = "Title") public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } @DynamoDBAttribute(attributeName = "ISBN") public String getISBN() { return ISBN; } public void setISBN(String ISBN) { this.ISBN = ISBN; } @DynamoDBAttribute(attributeName = "Price") public int getPrice() { return price; } public void setPrice(int price) { this.price = price; } @DynamoDBAttribute(attributeName = "PageCount") public int getPageCount() { return pageCount; } public void setPageCount(int pageCount) { this.pageCount = pageCount; } @DynamoDBAttribute(attributeName = "ProductCategory") public String getProductCategory() { return productCategory; } public void setProductCategory(String productCategory) { this.productCategory = productCategory; } @DynamoDBAttribute(attributeName = "InPublication") public boolean getInPublication() { return inPublication; } public void setInPublication(boolean inPublication) { this.inPublication = inPublication; } @Override public String toString() { return "Book [ISBN=" + ISBN + ", price=" + price + ", product category=" + productCategory + ", id=" + id + ", title=" + title + "]"; } } @DynamoDBTable(tableName = "ProductCatalog") public static class Bicycle { private int id; private String title; private String description; private String bicycleType; private String brand; private int price; private List<String> color; private String productCategory; @DynamoDBHashKey(attributeName = "Id") public int getId() { return id; } public void setId(int id) { this.id = id; } @DynamoDBAttribute(attributeName = "Title") public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } @DynamoDBAttribute(attributeName = "Description") public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } @DynamoDBAttribute(attributeName = "BicycleType") public String getBicycleType() { return bicycleType; } public void setBicycleType(String bicycleType) { this.bicycleType = bicycleType; } @DynamoDBAttribute(attributeName = "Brand") public String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } @DynamoDBAttribute(attributeName = "Price") public int getPrice() { return price; } public void setPrice(int price) { this.price = price; } @DynamoDBAttribute(attributeName = "Color") public List<String> getColor() { return color; } public void setColor(List<String> color) { this.color = color; } @DynamoDBAttribute(attributeName = "ProductCategory") public String getProductCategory() { return productCategory; } public void setProductCategory(String productCategory) { this.productCategory = productCategory; } @Override public String toString() { return "Bicycle [Type=" + bicycleType + ", color=" + color + ", price=" + price + ", product category=" + productCategory + ", id=" + id + ", title=" + title + "]"; } } @DynamoDBTable(tableName = "Reply") public static class Reply { private String id; private String replyDateTime; private String message; private String postedBy; // Partition key @DynamoDBHashKey(attributeName = "Id") public String getId() { return id; } public void setId(String id) { this.id = id; } // Range key @DynamoDBRangeKey(attributeName = "ReplyDateTime") public String getReplyDateTime() { return replyDateTime; } public void setReplyDateTime(String replyDateTime) { this.replyDateTime = replyDateTime; } @DynamoDBAttribute(attributeName = "Message") public String getMessage() { return message; } public void setMessage(String message) { this.message = message; } @DynamoDBAttribute(attributeName = "PostedBy") public String getPostedBy() { return postedBy; } public void setPostedBy(String postedBy) { this.postedBy = postedBy; } } @DynamoDBTable(tableName = "Thread") public static class Thread { private String forumName; private String subject; private String message; private String lastPostedDateTime; private String lastPostedBy; private Set<String> tags; private int answered; private int views; private int replies; // Partition key @DynamoDBHashKey(attributeName = "ForumName") public String getForumName() { return forumName; } public void setForumName(String forumName) { this.forumName = forumName; } // Range key @DynamoDBRangeKey(attributeName = "Subject") public String getSubject() { return subject; } public void setSubject(String subject) { this.subject = subject; } @DynamoDBAttribute(attributeName = "Message") public String getMessage() { return message; } public void setMessage(String message) { this.message = message; } @DynamoDBAttribute(attributeName = "LastPostedDateTime") public String getLastPostedDateTime() { return lastPostedDateTime; } public void setLastPostedDateTime(String lastPostedDateTime) { this.lastPostedDateTime = lastPostedDateTime; } @DynamoDBAttribute(attributeName = "LastPostedBy") public String getLastPostedBy() { return lastPostedBy; } public void setLastPostedBy(String lastPostedBy) { this.lastPostedBy = lastPostedBy; } @DynamoDBAttribute(attributeName = "Tags") public Set<String> getTags() { return tags; } public void setTags(Set<String> tags) { this.tags = tags; } @DynamoDBAttribute(attributeName = "Answered") public int getAnswered() { return answered; } public void setAnswered(int answered) { this.answered = answered; } @DynamoDBAttribute(attributeName = "Views") public int getViews() { return views; } public void setViews(int views) { this.views = views; } @DynamoDBAttribute(attributeName = "Replies") public int getReplies() { return replies; } public void setReplies(int replies) { this.replies = replies; } } @DynamoDBTable(tableName = "Forum") public static class Forum { private String name; private String category; private int threads; @DynamoDBHashKey(attributeName = "Name") public String getName() { return name; } public void setName(String name) { this.name = name; } @DynamoDBAttribute(attributeName = "Category") public String getCategory() { return category; } public void setCategory(String category) { this.category = category; } @DynamoDBAttribute(attributeName = "Threads") public int getThreads() { return threads; } public void setThreads(int threads) { this.threads = threads; } } }