DynamoDb Kotlin Module

Kotlin Module for the v2 dynamodb-enhanced SDK.

Adapting an idiomatic kotlin data model for use with the v2 dynamodb mapper is a pain, and full of compromises; data classes emulate a bean, which nullifies much of the advantages of data classes. This module provides a new TableSchema implementation that adds support for kotlin data classes.

• properties can be immutable; i.e. val is allowed
• properties don't need default values
• new annotations work directly on kotlin properties, rather than their getters

Install

Follow the instructions on Jitpack.

Requirements

Minimum Java 8. However, only 11 and 17 are officially supported.

Quickstart

// create a data class model, making sure to give it a partition key
data class Cat(
    @DynamoKtPartitionKey val name: String,
    val lives: Int = 9,
)

// use the new table schema provided by this module to init the table mapper
val tableSchema = DataClassTableSchema(Cat::class)
val cats = DynamoDbEnhancedClient.create().table("cats", tableScema)

// use the table mapper however you want!!
cats.createTable()
cats.putItem(Cat("Toggles"))

Annotations

The schema uses a new set of property-friendly annotations.

data class Appointment(
    @DynamoKtPartitionKey  // partition key for main index
    @DynamoKtAttribute(name = "owner_id")  // optionally rename the attribute
    val ownerId: UUID,
    
    @DynamoKtSortKey  // sort key for main index
    val id: UUID,
    
    @DynamoKtSecondaryPartitionKey(indexNames = ["names"])  // partition key for secondary indices
    val lastName: String,
    
    @DynamoKtSecondarySortKey(indexNames = ["names"])  // sort key for secondary indices
    val firstName: String,
    
    @DynamoKtConverted(InstantAsLongAttributeConverter::class)  // override the attribute converter
    val expires: Instant?,

    @DynamoKtFlatten // flatten properties of annotated class with this document    
    val metadata: Metadata
)

// If an instance of this type is empty, don't coerce it to null
@DynamoKtPreserveEmptyObject
data class Metadata(val created: Instant?, val refereceNumber: Int?)

Support for Extensions

Bean table extensions are supported. Register the extension to the client like normal, and then add the DynamoDbBean extension annotation to the getter of the property.

data class Post(
    @DynamoKtPartitionKey
    val id: UUID,
    
    val title: String,
    
    @get:DynamoDbVersionAttribute  // add extension annotation to the getter  (ie get:<annotation>)
    val version: Int
)

Gotchas

The DynamoDbAsyncClient.createTable method does not create the indices your table definition might have defined. This is unlike the DynamoDbClient, which, in recent versions of the AWS SDK, performs as you would expect.

To work around this, DynamoKt offers a createTableWithIndices extension method to provide the expected behaviour.

Samples

See the Samples