Serialization

Store JSON text

Use @Serialize for a property that should be stored as JSON text, such as a settings object or a list. The JSON library encodes the property into one string, and Kronos writes that string as a JDBC parameter; query results restore the property's Kotlin type. Choose the model tab that matches the JSON library and configure it when the application starts.

import com.kotlinorm.annotations.Serialize
import com.kotlinorm.annotations.Table
import com.kotlinorm.interfaces.KPojo

enum class Status { READY, CLOSED }

data class ProfileSetting(
    val theme: String,
    val shortcuts: List<String>
)

@Table("tb_user_profile")
data class UserProfile(
    var id: Int? = null,
    @Serialize
    var setting: ProfileSetting? = null,
    @Serialize
    var statuses: List<Status>? = null
) : KPojo

import com.kotlinorm.annotations.Serialize
import com.kotlinorm.annotations.Table
import com.kotlinorm.interfaces.KPojo
import kotlinx.serialization.Serializable

@Serializable
enum class Status { READY, CLOSED }

@Serializable
data class ProfileSetting(
    val theme: String,
    val shortcuts: List<String>
)

@Table("tb_user_profile")
data class UserProfile(
    var id: Int? = null,
    @Serialize
    var setting: ProfileSetting? = null,
    @Serialize
    var statuses: List<Status>? = null
) : KPojo

The setting and statuses properties above use VARCHAR columns by default. See 📚Column Types when an existing schema or table creation needs a specific column type.

Configure Gson

Add Gson and Kotlin reflection to the application, then register JSON text conversion once during startup. The same setup handles objects, lists, and nested values marked with @Serialize.

dependencies {
    implementation(kotlin("reflect"))
    implementation("com.google.code.gson:gson:2.14.0")
}

import com.google.gson.Gson
import com.kotlinorm.Kronos
import com.kotlinorm.interfaces.serializedValueCodec
import kotlin.reflect.jvm.javaType

val gson = Gson()

Kronos.registerValueCodec(
    serializedValueCodec(
        encode = { value, type -> gson.toJson(value, type.javaType) },
        decode = { text, type -> gson.fromJson(text, type.javaType) }
    )
)

Place this registration in the application's startup path, such as an Android Application or server bootstrap.

Configure Kotlinx Serialization

Enable the Kotlinx Serialization compiler plugin, add the JSON and reflection dependencies, and choose the Kotlinx Serialization model tab above.

plugins {
    id("org.jetbrains.kotlin.plugin.serialization") version "<your Kotlin version>"
}

dependencies {
    implementation(kotlin("reflect"))
    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.11.0")
}

import com.kotlinorm.Kronos
import com.kotlinorm.interfaces.serializedValueCodec
import kotlinx.serialization.KSerializer
import kotlinx.serialization.json.Json
import kotlinx.serialization.serializer

val json = Json {
    encodeDefaults = true
    ignoreUnknownKeys = true
}

Kronos.registerValueCodec(
    serializedValueCodec(
        encode = { value, type ->
            @Suppress("UNCHECKED_CAST")
            val valueSerializer = serializer(type) as KSerializer<Any>
            json.encodeToString(valueSerializer, value)
        },
        decode = { text, type -> json.decodeFromString(serializer(type), text) }
    )
)

Use the property normally

After configuration, construct, save, and query UserProfile with its regular Kotlin properties.

val profile = UserProfile(
    setting = ProfileSetting("dark", listOf("search", "save")),
    statuses = listOf(Status.READY, Status.CLOSED)
)
profile.insert().execute()

val loaded = UserProfile()
    .select()
    .where { it.id == 1 }
    .first()

println(loaded.setting?.theme)
println(loaded.statuses)

See 📚Enum Fields for scalar enum columns. See 📚Custom Value Mapping for domain values such as Money that use a scalar database column.