Greifen Sie als benutzerdefinierte Objekte auf erweiterte Dokumentattribute zu

Die Enhanced Document API bietet nicht nur eine API zum Lesen und Schreiben von Attributen mit schemalosen Strukturen, sondern ermöglicht auch die Konvertierung von Attributen in und aus Instanzen benutzerdefinierter Klassen.

Die Enhanced Document API verwendet AttributeConverterProvider s und AttributeConverter s, die im Abschnitt zur Konvertierung von Steuerattributen als Teil der DynamoDB Enhanced Client API angezeigt wurden.

Im folgenden Beispiel verwenden wir a CustomAttributeConverterProvider mit seiner verschachtelten AddressConverter Klasse, um Objekte zu konvertieren. Address

Dieses Beispiel zeigt, dass Sie Daten aus Klassen und auch Daten aus Strukturen kombinieren können, die nach Bedarf erstellt werden. Dieses Beispiel zeigt auch, dass benutzerdefinierte Klassen auf jeder Ebene einer verschachtelten Struktur verwendet werden können. Die Address Objekte in diesem Beispiel sind Werte, die in einer Map verwendet werden.

    public static void attributeToAddressClassMappingExample(DynamoDbEnhancedClient enhancedClient, DynamoDbClient standardClient) {
        String tableName = "customer";

        // Define the DynamoDbTable for an enhanced document.
        // The schema builder provides methods for attribute converter providers and keys.
        DynamoDbTable<EnhancedDocument> documentDynamoDbTable = enhancedClient.table(tableName,
                DocumentTableSchema.builder()
                        // Add the CustomAttributeConverterProvider along with the default when you build the table schema.
                        .attributeConverterProviders(
                                List.of(
                                        new CustomAttributeConverterProvider(),
                                        AttributeConverterProvider.defaultProvider()))
                        .addIndexPartitionKey(TableMetadata.primaryIndexName(), "id", AttributeValueType.N)
                        .addIndexSortKey(TableMetadata.primaryIndexName(), "lastName", AttributeValueType.S)
                        .build());
        // Create the DynamoDB table if needed.
        documentDynamoDbTable.createTable();
        waitForTableCreation(tableName, standardClient);


        // The getAddressesForCustomMappingExample() helper method that provides 'addresses' shows the use of a custom Address class
        // rather than using a Map<String, Map<String, String> to hold the address data.
        Map<String, Address> addresses = getAddressesForCustomMappingExample();

        // Build an EnhancedDocument instance to save an item with a mix of structures defined as needed and static classes.
        EnhancedDocument personDocument = EnhancedDocument.builder()
                .putNumber("id", 50)
                .putString("firstName", "Shirley")
                .putString("lastName", "Rodriguez")
                .putNumber("age", 53)
                .putNull("nullAttribute")
                .putJson("phoneNumbers", phoneNumbersJSONString())
                // Note the use of 'EnhancedType.of(Address.class)' instead of the more generic
                // 'EnhancedType.mapOf(EnhancedType.of(String.class), EnhancedType.of(String.class))' that was used in a previous example.
                .putMap("addresses", addresses, EnhancedType.of(String.class), EnhancedType.of(Address.class))
                .putList("hobbies", List.of("Hobby 1", "Hobby 2"), EnhancedType.of(String.class))
                .build();
        // Save the item to DynamoDB.
        documentDynamoDbTable.putItem(personDocument);

        // Retrieve the item just saved.
        EnhancedDocument srPerson = documentDynamoDbTable.getItem(Key.builder().partitionValue(50).sortValue("Rodriguez").build());

        // Access the addresses attribute.
        Map<String, Address> srAddresses = srPerson.get("addresses",
                EnhancedType.mapOf(EnhancedType.of(String.class), EnhancedType.of(Address.class)));

        srAddresses.keySet().forEach(k -> logger.info(addresses.get(k).toString()));

        documentDynamoDbTable.deleteTable();

// The content logged to the console shows that the saved maps were converted to Address instances.
Address{street='123 Main Street', city='Any Town', state='NC', zipCode='00000'}
Address{street='100 Any Street', city='Any Town', state='NC', zipCode='00000'}

CustomAttributeConverterProviderCode

public class CustomAttributeConverterProvider implements AttributeConverterProvider {

    private final Map<EnhancedType<?>, AttributeConverter<?>> converterCache = ImmutableMap.of(
            // 1. Add AddressConverter to the internal cache.
            EnhancedType.of(Address.class), new AddressConverter());

    public static CustomAttributeConverterProvider create() {
        return new CustomAttributeConverterProvider();
    }

    // 2. The enhanced client queries the provider for attribute converters if it
    //    encounters a type that it does not know how to convert.
    @SuppressWarnings("unchecked")
    @Override
    public <T> AttributeConverter<T> converterFor(EnhancedType<T> enhancedType) {
        return (AttributeConverter<T>) converterCache.get(enhancedType);
    }

    // 3. Custom attribute converter
    private class AddressConverter implements AttributeConverter<Address> {
        // 4. Transform an Address object into a DynamoDB map.
        @Override
        public AttributeValue transformFrom(Address address) {

            Map<String, AttributeValue> attributeValueMap = Map.of(
                    "street", AttributeValue.fromS(address.getStreet()),
                    "city", AttributeValue.fromS(address.getCity()),
                    "state", AttributeValue.fromS(address.getState()),
                    "zipCode", AttributeValue.fromS(address.getZipCode()));

            return AttributeValue.fromM(attributeValueMap);
        }

        // 5. Transform the DynamoDB map attribute to an Address oject.
        @Override
        public Address transformTo(AttributeValue attributeValue) {
            Map<String, AttributeValue> m = attributeValue.m();
            Address address = new Address();
            address.setStreet(m.get("street").s());
            address.setCity(m.get("city").s());
            address.setState(m.get("state").s());
            address.setZipCode(m.get("zipCode").s());

            return address;
        }

        @Override
        public EnhancedType<Address> type() {
            return EnhancedType.of(Address.class);
        }

        @Override
        public AttributeValueType attributeValueType() {
            return AttributeValueType.M;
        }
    }
}

Address-Klasse

public class Address {
                  private String street;
                  private String city;
                  private String state;
                  private String zipCode;

                  public Address() {
                  }

                  public String getStreet() {
                  return this.street;
                  }

                  public String getCity() {
                  return this.city;
                  }

                  public String getState() {
                  return this.state;
                  }

                  public String getZipCode() {
                  return this.zipCode;
                  }

                  public void setStreet(String street) {
                  this.street = street;
                  }

                  public void setCity(String city) {
                  this.city = city;
                  }

                  public void setState(String state) {
                  this.state = state;
                  }

                  public void setZipCode(String zipCode) {
                  this.zipCode = zipCode;
                  }
                  }

Hilfsmethode, die Adressen bereitstellt

Die folgende Hilfsmethode stellt die Map bereit, die benutzerdefinierte Address Instanzen für Werte anstelle von generischen Map<String, String> Instanzen für Werte verwendet.

    private static Map<String, Address> getAddressesForCustomMappingExample() {
        Address homeAddress = new Address();
        homeAddress.setStreet("100 Any Street");
        homeAddress.setCity("Any Town");
        homeAddress.setState("NC");
        homeAddress.setZipCode("00000");

        Address workAddress = new Address();
        workAddress.setStreet("123 Main Street");
        workAddress.setCity("Any Town");
        workAddress.setState("NC");
        workAddress.setZipCode("00000");

        return Map.of("home", homeAddress,
                "work", workAddress);
    }