DynamoDB-enhanced: Add support for polymorphic subtypes to mapper #2861
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| { | ||
| "category": "DynamoDB Enhanced Client", | ||
| "contributor": "bmaizels", | ||
| "type": "feature", | ||
| "description": "Added support for polymorphic mapping of subtypes to better support single-table design." | ||
| } |
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| ## Overview | ||
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| A library that enhances DynamoDB operations by directly mapping your Java data objects to and from records in your | ||
| DynamoDB tables. | ||
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| ## Getting Started | ||
| All the examples below use a fictional Customer class. This class is | ||
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@@ -253,6 +254,85 @@ how Lombok's 'onMethod' feature is leveraged to copy the attribute based DynamoD | |
| } | ||
| ``` | ||
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| ### Using subtypes to assist with single-table design | ||
| It's considered a best practice in some situations to combine entities of various types into a single table in DynamoDb | ||
| to enable the querying of multiple related entities without the need to actually join data across multiple tables. The | ||
| enhanced client assists with this by supporting polymorphic mapping into distinct subtypes. | ||
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| Let's say you have a customer: | ||
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| ```java | ||
| public class Customer { | ||
| String getCustomerId(); | ||
| void setId(String id); | ||
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| String getName(); | ||
| void setName(String name); | ||
| } | ||
| ``` | ||
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| And an order that's associated with a customer: | ||
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| ```java | ||
| public class Order { | ||
| String getOrderId(); | ||
| void setOrderId(); | ||
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| String getCustomerId(); | ||
| void setCustomerId(); | ||
| } | ||
| ``` | ||
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| You could choose to store both of these in a single table that is indexed by customer ID, and create a TableSchema that | ||
| is capable of mapping both types of entities into a common supertype: | ||
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| ```java | ||
| import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbBean; | ||
| import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbPartitionKey; | ||
| import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbSubtypeName; | ||
| import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbSubtypes; | ||
| import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbSubtypes.Subtype; | ||
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| @DynamoDbBean | ||
| @DynamoDbSubtypes({ | ||
| @Subtype(name = "CUSTOMER", subtypeClass = Customer.class), | ||
| @Subtype(name = "ORDER", subtypeClass = Order.class)}) | ||
| public class CustomerRelatedEntity { | ||
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There was a problem hiding this comment. This can be abstract and/or the annotation enforce that ( I see its abstract in code below) There was a problem hiding this comment. Java code would be way neater if this could be an interface and classes implementing it. Is that a feasible option? There was a problem hiding this comment. @dvlato could you elaborate on exactly what you are proposing? Maybe with an example? |
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| @DynamoDbSubtypeName | ||
| String getEntityType(); | ||
| void setEntityType(); | ||
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| @DynamoDbPartitionKey | ||
| String getCustomerId(); | ||
| void setCustomerId(); | ||
| } | ||
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| @DynamoDbBean | ||
| public class Customer extends CustomerRelatedEntity { | ||
| String getName(); | ||
| void setName(String name); | ||
| } | ||
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| @DynamoDbBean | ||
| public class Order extends CustomerRelatedEntity { | ||
| String getOrderId(); | ||
| void setOrderId(); | ||
| } | ||
| ``` | ||
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| Now all you have to do is create a TableSchema that maps the supertype class: | ||
| ```java | ||
| TableSchema<CustomerRelatedEntity> tableSchema = TableSchema.fromClass(CustomerRelatedEntity.class); | ||
| ``` | ||
| Now you have a `TableSchema` that can map any objects of both `Customer` and `Order` and write them to the table, | ||
| and can also read any record from the table and correctly instantiate it using the subtype class. So it's now possible | ||
| to write a single query that will return both the customer record and all order records associated with a specific | ||
| customer ID. | ||
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| As with all the other `TableSchema` implementations, a static version is provided that allows reflective introspection | ||
| to be skipped entirely and is recommended for applications where cold-start latency is critical. See the javadocs for | ||
| `StaticPolymorphicTableSchema` for an example of how to use this. | ||
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| ### Non-blocking asynchronous operations | ||
| If your application requires non-blocking asynchronous calls to | ||
| DynamoDb, then you can use the asynchronous implementation of the | ||
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| /* | ||
| * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"). | ||
| * You may not use this file except in compliance with the License. | ||
| * A copy of the License is located at | ||
| * | ||
| * http://aws.amazon.com/apache2.0 | ||
| * | ||
| * or in the "license" file accompanying this file. This file is distributed | ||
| * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either | ||
| * express or implied. See the License for the specific language governing | ||
| * permissions and limitations under the License. | ||
| */ | ||
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| package software.amazon.awssdk.enhanced.dynamodb.internal.mapper; | ||
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| import java.util.Optional; | ||
| import java.util.function.Consumer; | ||
| import software.amazon.awssdk.annotations.SdkInternalApi; | ||
| import software.amazon.awssdk.enhanced.dynamodb.AttributeValueType; | ||
| import software.amazon.awssdk.enhanced.dynamodb.TableMetadata; | ||
| import software.amazon.awssdk.enhanced.dynamodb.mapper.StaticAttributeTag; | ||
| import software.amazon.awssdk.enhanced.dynamodb.mapper.StaticTableMetadata; | ||
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| @SdkInternalApi | ||
| public class SubtypeNameTag implements StaticAttributeTag { | ||
| private static final SubtypeNameTag INSTANCE = new SubtypeNameTag(); | ||
| private static final String CUSTOM_METADATA_KEY = "SubtypeName"; | ||
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| private SubtypeNameTag() { | ||
| } | ||
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| public static Optional<String> resolve(TableMetadata tableMetadata) { | ||
| return tableMetadata.customMetadataObject(CUSTOM_METADATA_KEY, String.class); | ||
| } | ||
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| @Override | ||
| public Consumer<StaticTableMetadata.Builder> modifyMetadata(String attributeName, | ||
| AttributeValueType attributeValueType) { | ||
| if (!AttributeValueType.S.equals(attributeValueType)) { | ||
| throw new IllegalArgumentException( | ||
| String.format("Attribute '%s' of type %s is not a suitable type to be used as a subtype name. Only string is " | ||
| + "supported for this purpose.", attributeName, attributeValueType.name())); | ||
| } | ||
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| return metadata -> | ||
| metadata.addCustomMetadataObject(CUSTOM_METADATA_KEY, attributeName); | ||
| } | ||
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| public static SubtypeNameTag create() { | ||
| return INSTANCE; | ||
| } | ||
| } |
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I think it would be useful to highlight here a sample multi-schema table for matching the proposed annotations