Kotlin Data Class DynamoDB Mapper

AWS has finally released a kotlin sdk, but it does not include a 'nice' way to map things

This project intends to make mapping between dynamo db types and domain types easy.

Usage

Build file

In your build.gradle.kts file dependencies section

    implementation("com.kncept.ddb.mapper:mapper:1.0.4")

Note you will also need to define dependencies, something like:

    implementation("aws.sdk.kotlin:aws-core:$awsKotlinSdkVersion")
    implementation("aws.sdk.kotlin:dynamodb:$awsKotlinSdkVersion")

You may need implementation(kotlin("reflect")), I'm not sure. This will be tested and docs updated.

Using the type mapper

Create an instance. It comes pre-configured with a reasonable set of defaults.

    val mapper = DynamoDbTypeMapper()

In order to use the results, code similar to the following should be used.

        
        val attributes: Map<String, AttributeValue> = mapper.toAttributes(item)
        val items: List<Item> = results.items.map { mapper.toItem(Item::class, it)}

Configuration

There is a limited amount of configuration available, and the defaults should be sufficient for most use cases. That said, there is always the need to do more at times, and

Module Config

Some modules have configuration. For example, in order to disable epoch second resolution on an Instant, set the truncateTypesToEpochSecond variable to true and re-register the module.

Custom Type Mappers

first create your custom type mapper:

    class MyTypeMapper: TypeMapper<Boolean> { ... }

then register it by calling

    mapper.register(MyTypeMapper())

Or you can use the annotation, at the field or class level

    @MappedBy(MyTypeMapper::class)

Collections and arrays are supported, but may not work for all cases, due to generics.
If auto detection fails, you can speficy the type with the following annotation

    @MappedCollection(MyType::class) val things: List<*>

Mapper config

There are some configuration options available for the Mapper. Just update the option and it will take effect.

    mapper.emitNulls = true

Acknowledgements

Inspired by https://github.com/oharaandrew314/dynamodb-kotlin-module