Using reflection-based serialization for Kotlin data classes in MongoDB and the official Kotlin driver

The official MongoDB Kotlin driver includes a reflection-based serializer for Kotlin data classes.

• Simpler for basic usage. No configuration, no annotations, no compiler plugin.
• Slower. Reflection can be more than 10× slower than KotlinX.Serialization.
• Rigid. Inheritance and polymorphism use the Java driver's codec system.

Configuration

plugins {
    kotlin("jvm") version "2.3.21"
}

dependencies {
    implementation("org.mongodb:bson-kotlin:VERSION") //(1)!

    // Choose one of:
    implementation("dev.opensavvy.ktmongo:driver-coroutines:VERSION") //(2)!
    implementation("dev.opensavvy.ktmongo:driver-sync:VERSION") //(3)!
    implementation("dev.opensavvy.ktmongo:bson-official:VERSION") //(4)!
}

1. The official reflection support module. View versions.
2. KtMongo's coroutine-aware MongoDB driver. Recommended for new projects. View versions
3. KtMongo's blocking MongoDB driver. Recommended if you have an existing blocking codebase. View versions
4. KtMongo's BSON types, without MongoDB DSL. Useful for creating libraries or reusable utilities. View versions

Writing serializable classes

Kotlin data classes are supported.

data class User(
    val _id: ObjectId,
    val name: String,
    val age: Int? = null,
)

Here is a non-exhaustive list of unsupported situations:

• private classes.
• Local classes.
• Non-data classes.