DynamoDB Enhanced to support immutable Kotlin data classes

In Kotlin your goal is to use data classes as immutable. With the current mapper this is not possible. You have to add an parameter less constructor to the class (noargs plugin) and all fields has to be changeable (var’s instead val’s)

Example: data class Example(val name:String) and not data class Example(var name:String)

Describe the Feature

The DynamoDB Enhanced mapper should call the constructor with all attributes read from the dynamodb.

Is your Feature Request related to a problem?

You can’t use immutable data classes and you have to use the norags plugin.

Describe alternatives you’ve considered

Use var’s instead of val’s and use norags plugin:

plugins{
   id("org.jetbrains.kotlin.plugin.noarg") version "1.4.10"
}
noArg {
  annotation("software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbBean")
}

Your Environment

• AWS Java SDK version used: 2.15.7
• JDK version used: 11
• Operating System and version: Mac 10.15.7

[cmaus-cs]

The builder’s set methods are supposed to return a builder instance. kotlin generated setters that return void.

The following works for me, but is quite tedious to write:

@DynamoDbImmutable(builder = TweetDocument.Builder::class)
class TweetDocument(
    @get:DynamoDbPartitionKey val partitionKey: String,
    @get:DynamoDbSortKey val sortKey: String,
    val tweetId: Long,
    val searchTerm: String,
    val text: String,
    val lang: String,
    val createdAt: String
) {

    companion object {
        @JvmStatic
        fun builder() = Builder()
    }

    class Builder {
        private var partitionKey: String? = null
        fun partitionKey(value: String) = apply { partitionKey = value }

        private var sortKey: String? = null
        fun sortKey(value: String) = apply { sortKey = value }

        private var tweetId: Long? = null
        fun tweetId(value: Long) = apply { tweetId = value }

        private var searchTerm: String? = null
        fun searchTerm(value: String) = apply { searchTerm = value }

        private var text: String? = null
        fun text(value: String) = apply { text = value }

        private var lang: String? = null
        fun lang(value: String) = apply { lang = value }

        private var createdAt: String? = null
        fun createdAt(value: String) = apply { createdAt = value }

        fun build() = TweetDocument(
            partitionKey!!,
            sortKey!!,
            tweetId!!,
            searchTerm!!,
            text!!,
            lang!!,
            createdAt!!
        )
    }
}

[oharaandrew314]

I made a plugin that allows you to use a data class directly with the DataClassTableSchema; might be worth checking out. https://github.com/oharaandrew314/dynamodb-kotlin-module