Convert Dynamic JSON Keys to Kotlin Map Types

Dynamic JSON Keys with Kotlin Maps

When a JSON object has keys that are not known at compile time, you cannot define a data class with fixed properties. Instead, use Kotlin's Map<String, T> type.

Example JSON

{
  "metrics": {
    "cpu_usage": 72.5,
    "memory_usage": 85.3,
    "disk_io": 45.1
  },
  "labels": {
    "env": "production",
    "region": "us-east-1"
  }
}

Generated Kotlin

data class Dashboard(
    val metrics: Map<String, Double>,
    val labels: Map<String, String>
)

Mixed Value Types

When values have different types, use Map<String, Any> or Map<String, JsonElement> with kotlinx.serialization:

{
  "settings": {
    "theme": "dark",
    "fontSize": 14,
    "autoSave": true
  }
}

data class Config(
    val settings: Map<String, JsonElement>
)

Accessing Map Values

val cpuUsage = dashboard.metrics["cpu_usage"] // Double?
val env = dashboard.labels["env"] ?: "unknown"

// Iterate over all entries
dashboard.metrics.forEach { (key, value) ->
    println("$key: $value")
}

Map vs Data Class Decision

Use a data class when:

• Keys are known and fixed
• You want compile-time property access

Use a Map when:

• Keys are dynamic, user-defined, or vary between responses
• The object acts as a key-value store

Nested Maps

data class Config(
    val sections: Map<String, Map<String, String>>
)

This handles JSON structures like { "database": { "host": "...", "port": "..." }, "cache": { ... } } where both levels have dynamic keys.