Custom Value Mapping

User-facing custom domain value mapping.

Store a domain value in one column

Custom value mapping keeps a domain value in Kotlin while saving one database-friendly value in a column. This example stores Money as whole cents in a BIGINT column.

Define the model

import com.kotlinorm.annotations.ColumnType
import com.kotlinorm.annotations.PrimaryKey
import com.kotlinorm.annotations.Table
import com.kotlinorm.enums.KColumnType
import com.kotlinorm.interfaces.KPojo

data class Money(val cents: Long)

@Table("tb_invoice")
data class Invoice(
    @PrimaryKey(identity = true)
    var id: Long? = null,
    @ColumnType(KColumnType.BIGINT)
    var total: Money? = null,
) : KPojo

Register the conversion

A valueCodec describes how a value travels between a model and its column. Register this Money conversion during application startup. supports selects Money properties, and convert writes cents or rebuilds Money. The direction is ENCODE while saving and DECODE while reading.

import com.kotlinorm.Kronos
import com.kotlinorm.enums.ValueCodecDirection
import com.kotlinorm.interfaces.valueCodec

Kronos.registerValueCodec(
    valueCodec(
        supports = { value, context ->
            context.targetType.classifier == Money::class &&
                when (context.direction) {
                    ValueCodecDirection.ENCODE -> value is Money
                    ValueCodecDirection.DECODE -> value is Number
                }
        },
        convert = { value, context ->
            when (context.direction) {
                ValueCodecDirection.ENCODE -> (value as Money).cents
                ValueCodecDirection.DECODE -> Money((value as Number).toLong())
            }
        }
    )
)

The type check keeps the conversion on properties declared as Money. For example, Money(1_999) is stored as 1999.

Use Money normally

After registration, application code creates and queries Invoice with Money values.

import com.kotlinorm.orm.insert.insert
import com.kotlinorm.orm.select.select

val invoiceId = requireNotNull(
    Invoice(total = Money(1_999))
        .insert()
        .withId()
        .execute()
        .lastInsertId
)

val loaded = Invoice()
    .select()
    .where { it.id == invoiceId }
    .first()

println(loaded.total?.cents)

Choose the mapping