映射任意数据 - Amazon DynamoDB
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映射任意数据

除支持的 Java 类型（请参阅 DynamoDB Mapper for Java 支持的数据类型）外，您还可以使用应用程序中不能直接映射到 Amazon DynamoDB 类型的类型。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对象时转换数据。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 对象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 为 DynamoDB 中的代码示例创建表和加载数据 部分的说明，将数据加载到您的帐户的 DynamoDB。

有关运行以下示例的分步说明，请参阅 Java 代码示例。

例 
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;
        }
    }
}