Amazon DynamoDB
开发人员指南 (API Version 2012-08-10)
AWS 服务或AWS文档中描述的功能,可能因地区/位置而异。点 击 Getting Started with Amazon AWS to see specific differences applicable to the China (Beijing) Region.

映射任意数据

除支持的 Java 类型 (请参阅受支持数据类型) 外,您还可以在应用程序中使用不能直接映射到 DynamoDB 的类型。要映射这些类型,您必须提供一种实现来将复杂类型转换为 DynamoDB 支持的类型 (反之亦然),并且使用 @DynamoDBTypeConverted 注释来注释这一复杂类型访问器方法。转换器代码会在保存或加载数据元时转换数据。另外,所有使用复杂类型的操作都可以使用转换器代码。请注意,当您在查询和扫描操作期间比较数据时,比较所针对的是 DynamoDB 中存储的数据。

例如,看看以下 CatalogItem 类,它定义了 Dimension 属性 (属于 DimensionType)。此属性将以高度、宽度和厚度的形式存储项目尺寸。假定您决定将这些项目尺寸存储为 DynamoDB 中的字符串 (例如 8.5x11x.05)。以下示例提供可将 DimensionType 数据元转换为字符串并将字符串转换为 DimensionType 的转换器代码。

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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package com.amazonaws.codesamples.datamodeling; import java.io.IOException; import java.util.Arrays; import java.util.HashSet; import java.util.Set; import com.amazonaws.regions.Regions; 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.DynamoDBTypeConverted; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTypeConverter; import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable; public class DynamoDBMapperExample { static AmazonDynamoDB client; public static void main(String[] args) throws IOException { // Set the AWS region you want to access. Regions usWest2 = Regions.US_WEST_2; client = AmazonDynamoDBClientBuilder.standard().withRegion(usWest2).build(); DimensionType dimType = new DimensionType(); dimType.setHeight("8.00"); dimType.setLength("11.0"); dimType.setThickness("1.0"); Book book = new Book(); book.setId(502); book.setTitle("Book 502"); book.setISBN("555-5555555555"); book.setBookAuthors(new HashSet<String>(Arrays.asList("Author1", "Author2"))); book.setDimensions(dimType); DynamoDBMapper mapper = new DynamoDBMapper(client); mapper.save(book); Book bookRetrieved = mapper.load(Book.class, 502); System.out.println("Book info: " + "\n" + bookRetrieved); bookRetrieved.getDimensions().setHeight("9.0"); bookRetrieved.getDimensions().setLength("12.0"); bookRetrieved.getDimensions().setThickness("2.0"); mapper.save(bookRetrieved); bookRetrieved = mapper.load(Book.class, 502); System.out.println("Updated book info: " + "\n" + bookRetrieved); } @DynamoDBTable(tableName = "ProductCatalog") public static class Book { private int id; private String title; private String ISBN; private Set<String> bookAuthors; private DimensionType dimensionType; // Partition key @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 = "Authors") public Set<String> getBookAuthors() { return bookAuthors; } public void setBookAuthors(Set<String> bookAuthors) { this.bookAuthors = bookAuthors; } @DynamoDBTypeConverted(converter = DimensionTypeConverter.class) @DynamoDBAttribute(attributeName = "Dimensions") public DimensionType getDimensions() { return dimensionType; } @DynamoDBAttribute(attributeName = "Dimensions") public void setDimensions(DimensionType dimensionType) { this.dimensionType = dimensionType; } @Override public String toString() { return "Book [ISBN=" + ISBN + ", bookAuthors=" + bookAuthors + ", dimensionType= " + dimensionType.getHeight() + " X " + dimensionType.getLength() + " X " + dimensionType.getThickness() + ", Id=" + id + ", Title=" + title + "]"; } } static public class DimensionType { private String length; private String height; private String thickness; public String getLength() { return length; } public void setLength(String length) { this.length = length; } public String getHeight() { return height; } public void setHeight(String height) { this.height = height; } public String getThickness() { return thickness; } public void setThickness(String thickness) { this.thickness = thickness; } } // Converts the complex type DimensionType to a string and vice-versa. static public class DimensionTypeConverter implements DynamoDBTypeConverter<String, DimensionType> { @Override public String convert(DimensionType object) { DimensionType itemDimensions = (DimensionType) object; String dimension = null; try { if (itemDimensions != null) { dimension = String.format("%s x %s x %s", itemDimensions.getLength(), itemDimensions.getHeight(), itemDimensions.getThickness()); } } catch (Exception e) { e.printStackTrace(); } return dimension; } @Override public DimensionType unconvert(String s) { DimensionType itemDimension = new DimensionType(); try { if (s != null && s.length() != 0) { String[] data = s.split("x"); itemDimension.setLength(data[0].trim()); itemDimension.setHeight(data[1].trim()); itemDimension.setThickness(data[2].trim()); } } catch (Exception e) { e.printStackTrace(); } return itemDimension; } } }