Supported Types

The table below shows every Kotlin type Kiln can persist, the SQLite column type used, and the bind/read method the generated code uses internally.

Primitive types

Kotlin type	SQLite type	Notes
String	TEXT	Stored as-is
Int	INTEGER	Upcast to Long for SQLite bind; read back and downcast
Long	INTEGER	Native SQLite integer type
Short	INTEGER	Upcast to Long for bind; downcast on read
Double	REAL	Native SQLite real type
Float	REAL	Upcast to Double for bind; downcast on read
Boolean	INTEGER	true → 1, false → 0; read back via getLong() == 1L
ByteArray	BLOB	Stored as raw bytes

Date / time types

Kotlin type	SQLite type	Format stored	Notes
kotlinx.datetime.LocalDate	TEXT	ISO-8601 (YYYY-MM-DD)	Serialized via .toString(), parsed via LocalDate.parse()
kotlinx.datetime.LocalDateTime	TEXT	ISO-8601 (YYYY-MM-DDTHH:MM:SS)	Serialized via .toString(), parsed via LocalDateTime.parse()
kotlinx.datetime.Instant	TEXT	ISO-8601 with UTC offset	Serialized via .toString(), parsed via Instant.parse()

Sorting by date works naturally

ISO-8601 strings sort lexicographically in the same order as their chronological order, so ORDER BY and range predicates on date columns work correctly without any special handling.

Enum classes

Kotlin type	SQLite type	Stored as	Read back via
Any enum class	TEXT	enumValue.name	MyEnum.valueOf(getString())

enum class Status { TODO, IN_PROGRESS, DONE, CANCELLED }

@DbEntity(tableName = "tasks")
data class Task(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    val status: Status = Status.TODO   // stored as "TODO", "IN_PROGRESS", etc.
)

Renaming enum values is a breaking change

If you rename a Status.IN_PROGRESS to Status.ACTIVE, rows with "IN_PROGRESS" stored will throw IllegalArgumentException when read. Migrate existing rows (update the text value in the database) before renaming.

Nullable types

Any of the types above can be made nullable by appending ?:

Kotlin type	SQLite type	Behaviour
String?	TEXT	Column allows NULL; null Kotlin value stored as SQL NULL
Long?	INTEGER	Column allows NULL
Boolean?	INTEGER	null stored as SQL NULL; true → 1, false → 0
(any type)?	same base type	NULL allowed, null written and read correctly

Unsupported types

If a property type is not in the tables above and is not annotated with @Ignore, the KSP processor emits a build error:

e: Kiln: type 'List<String>' is not supported.
   Annotate the property with @Ignore or use a supported type.
   File: com/example/MyEntity.kt:12

Common workarounds:

Unsupported type	Workaround
List<T>, Set<T>	Serialize to JSON string; store as String with @Ignore on the typed property
Map<K,V>	Serialize to JSON string
Custom class	Store each field as a separate @Column, or serialize to String
java.util.Date	Migrate to kotlinx.datetime.Instant (natively supported)
java.time.LocalDate	Use kotlinx.datetime.LocalDate instead