Dynamo Mapper

A simple mapper for converting to and from DynamoDB AttributeValues and POJOs using Jackson.

In development

Dynamo Mapper is still in development. Currently, only single gets, puts, updates, and deletes are supported. More is planned in the future and submissions are welcome.

Installation

Dynamo Mapper is available from Maven Central.

Gradle

implementation 'com.autonomouslogic.dynamomapper:dynamo-mapper:version'

Maven

<dependency>
    <groupId>com.autonomouslogic.dynamomapper</groupId>
    <artifactId>dynamo-mapper</artifactId>
    <version>version</version>
</dependency>

Usage

Dynamo Mapper functions as a wrapper around the existing AWS DynamoDB v2 SDK. First, you need to construct a DynamoDB client object and a Jackson ObjectMapper, and then pass those to the Dynamo Mapper builder. If you do not provide a DynamoDB client or Jackson ObjectMapper, defaults will be used.

var dynamoMapper = DynamoMapper.builder()
    .client(DynamoDbClient.create())
    .objectMapper(new ObjectMapper())
    .tableNameDecorator(decorator) // optional
    .build();

Or, for the asynchronous API:

var asyncDynamoMapper = DynamoAsyncMapper.builder()
    .client(DynamoDbAsyncClient.create())
    .objectMapper(new ObjectMapper())
	.tableNameDecorator(decorator) // optional
    .build();

Defining schemas

Dynamo Mapper relies on Jackson for its serialization. Generally, anything that works in Jackson will work in Dynamo Mapper. Only a few extra annotations are required.

@DynamoTableName("table-name")
public class ModelObject {
	@JsonProperty
	@DynamoPrimaryKey
	private String primaryKey;
	
	@JsonProperty
	private String otherValue;
	
	/* etc. */
}

Getting items

Using the synchronous API:

var item = dynamoMapper.getItemFromPrimaryKey("key-value", ModelObject.class).item();

Using the asynchronous API:

dynamoMapper.getItemFromPrimaryKey("key-value", ModelObject.class).thenAccept(response -> {
	var item = response.item();
});

Putting items

Using the synchronous API:

var item = new ModelObject().setPrimaryKey("key-value");
var response = dynamoMapper.putItemFromKeyObject(item);

Using the asynchronous API:

var item = new ModelObject().setPrimaryKey("key-value");
dynamoMapper.putItemFromKeyObject(item).thenAccept(response -> {
	// etc.
});

Best practices

• Jackson will include all null values, to prevent this taking up space in DynamoDB, use @JsonInclude(JsonInclude.Include.NON_NULL)
• To properly serialize BigDecimals, use objectMapper.enable(JsonGenerator.Feature.WRITE_BIGDECIMAL_AS_PLAIN)
• To encode java.time objects properly, use jackson-datatype-jsr310

Comparison with DynamoDBMapper and DynamoDB Enhanced

The DynamoDBMapper in the v1 AWS SDK and the DynamoDB Enhanced Client in the v2 AWS SDK both provide similar mapping functionality.

This idea for this library was originally created to provide the same mapping as the v1 mapper, but for the v2 SDK, before the enhanced client was released. The v2 SDK now provides this mapping functionality officially, but has a few short-comings. For instance, the annotations must be added to methods and not properties. This makes Lombok models useless. Jackson is a widely used and mature library. with advanced features that will never, and shouldn't, be implemented in the enhanced client.

There are some cons to doing it this way. For instance, it's not possible to have a different schema in the DynamoDB and JSON versions of an object.

Feature	Dynamo Mapper	DynamoDBMapper (v1)	DynamoDb Enhanced Client (v2)
Synchronous API	Yes	Yes	Yes
Asynchronous API	Yes	No	Yes
Lombok compatible	Yes	Partial?	No?

Resources

• https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_AttributeValue.html
• https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.NamingRulesDataTypes.html
• https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBMapper.html
• https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/dynamodb-enhanced-client.html
• https://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/dynamodbv2/package-summary.html
• https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/dynamodb/package-summary.html

Versioning

Dynamo Mapper follows semantic versioning.

Code Style

Dynamo Mapper follows Palantir with tabs. Automatic code formatting can be done by running ./gradlew spotlessApply.

License

Dynamo Mapper is licensed under the MIT-0 license.

Status

Type	Status
LGTM
CodeClimate
SonarCloud
Libraries.io
Snyk
Codecov
Synatype Lift	link