Column Types

Kotlin type inference

Kronos chooses a column type from each persisted KPojo property when the property has no 📚Annotations. The selected database dialect renders the final DDL type when the table is created or synchronized.

import com.kotlinorm.annotations.Table
import com.kotlinorm.interfaces.KPojo
import java.time.LocalDateTime

@Table("tb_type_profile")
data class TypeProfile(
    var enabled: Boolean? = null,
    var score: Int? = null,
    var payload: ByteArray? = null,
    var createdAt: LocalDateTime? = null,
) : KPojo

For this model, Kronos selects the following column types:

Property	Inferred `KColumnType`
`enabled`	`BIT`
`score`	`INT`
`payload`	`BLOB`
`createdAt`	`DATETIME`

MySQL renders those columns as:

`enabled` TINYINT(1)
`score` INT(11)
`payload` BLOB
`createdAt` DATETIME

Default mapping

Use this table as a compact reference for automatic mapping. The selected database dialect renders the final DDL type; see 📚Column Type Reference for dialect examples.

Kotlin type	Inferred `KColumnType`
`kotlin.Boolean`	`BIT`
`kotlin.Byte`	`TINYINT`
`kotlin.Short`	`SMALLINT`
`kotlin.Int`	`INT`
`kotlin.Long`	`BIGINT`
`kotlin.Float`	`FLOAT`
`kotlin.Double`	`DOUBLE`
`java.math.BigDecimal`	`DECIMAL`
`kotlin.Char`	`CHAR`
`kotlin.String`	`VARCHAR`
`java.util.Date`, `java.sql.Date`, `java.time.LocalDate`, `kotlinx.datetime.LocalDate`	`DATE`
`java.time.LocalTime`, `kotlinx.datetime.LocalTime`	`TIME`
`java.time.LocalDateTime`, `kotlinx.datetime.LocalDateTime`	`DATETIME`
`java.sql.Timestamp`	`TIMESTAMP`
`kotlin.time.Instant`, `kotlinx.datetime.Instant`	`TIMESTAMP`
`kotlin.ByteArray`	`BLOB`
Scalar enum	`VARCHAR`
`@Serialize` property	`VARCHAR` unless `@ColumnType` overrides it
Other property types	`VARCHAR`

Scalar enums use Enum.name for string-compatible columns. An integer @ColumnType stores the enum position. Use a custom mapping for a business code, and see 📚Enum Fields for examples.

Override with `@ColumnType`

Use @ColumnType to select the column type for one property.

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

@Table("tb_override_type")
data class OverrideType(
    @ColumnType(KColumnType.TEXT)
    var bio: String? = null,
    @ColumnType(KColumnType.UUID)
    var externalId: String? = null,
) : KPojo

For this model, the selected column types are:

Property	`KColumnType`
`bio`	`TEXT`
`externalId`	`UUID`

PostgreSQL renders them as:

"bio" TEXT
"externalId" UUID

Set `length` and `scale`

The @ColumnType annotation also accepts length and scale. String-like types use length; decimal types use length and scale.

import com.kotlinorm.annotations.ColumnType
import com.kotlinorm.annotations.Table
import com.kotlinorm.enums.KColumnType
import com.kotlinorm.interfaces.KPojo
import java.math.BigDecimal

@Table("tb_invoice_line")
data class InvoiceLine(
    @ColumnType(KColumnType.VARCHAR, length = 80)
    var title: String? = null,
    @ColumnType(KColumnType.DECIMAL, length = 12, scale = 2)
    var amount: BigDecimal? = null,
) : KPojo

DDL type fragments:

Dialect	`title`	`amount`
MySQL	`VARCHAR(80)`	`DECIMAL(12,2)`
PostgreSQL	`VARCHAR(80)`	`DECIMAL(12,2)`
SQLite	`TEXT`	`NUMERIC`
H2	`VARCHAR(80)`	`NUMERIC(12,2)`
SQLServer	`VARCHAR(80)`	`DECIMAL(12,2)`
Oracle	`VARCHAR2(80)`	`NUMBER(12,2)`
DM8	`VARCHAR2(80)`	`NUMBER(12,2)`

Use a native JSON column

With the Gson or Kotlinx Serialization setup shown on 📚Serialization, @Serialize properties are encoded as JSON text. Add @ColumnType with KColumnType.JSON when the database table should use a native JSON column.

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

data class AuditPayload(val ip: String, val tags: List<String>)

@Table("tb_audit_event")
data class AuditEvent(
    @ColumnType(KColumnType.JSON)
    @Serialize
    var payload: AuditPayload? = null,
) : KPojo

When the registered JSON configuration saves AuditPayload("127.0.0.1", listOf("login")), the insert parameter is:

payload -> {"ip":"127.0.0.1","tags":["login"]}