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Add create custom column on FAQ (#21)

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Add create custom column on FAQ
This commit is contained in:
Guilherme Salustiano
2021-12-29 06:57:36 -03:00
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commit 01cf93e635
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@@ -92,5 +92,41 @@ A: You need to define your own! See examples:
[#855](https://github.com/JetBrains/Exposed/issues/855)
https://stackoverflow.com/a/61940820/1155026
### Q: How create custom collumn type
A: Just implements [IColumnType](https://github.com/JetBrains/Exposed/blob/76a671e57a0105d6aed79e256c088690bd4a56b6/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/ColumnType.kt#L25)
and use [registerColumn](https://github.com/JetBrains/Exposed/blob/76a671e57a0105d6aed79e256c088690bd4a56b6/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Table.kt#L387)
to [extends](https://kotlinlang.org/docs/extensions.html) a [Table](https://github.com/JetBrains/Exposed/blob/76a671e57a0105d6aed79e256c088690bd4a56b6/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Table.kt#L326)
eg: **Create custom UUID types (inpired by [@pjagielski article](https://medium.com/@pjagielski/how-we-use-kotlin-with-exposed-at-touk-eacaae4565b5#e4e4))**
```kotlin
abstract class TypedId(open val id: UUID): Serializable, Comparable<TypedId> {
override fun compareTo(other: TypedId) = this.id.compareTo(other.id)
}
class TypedUUIDColumnType<T: TypedId>(val constructor: (UUID) -> T, private val uuidColType: UUIDColumnType = UUIDColumnType()): IColumnType by uuidColType {
override fun valueFromDB(value: Any) = constructor(uuidColType.valueFromDB(value))
override fun notNullValueToDB(value: Any): Any = uuidColType.notNullValueToDB(valueUnwrap(value))
override fun nonNullValueToString(value: Any): String = uuidColType.nonNullValueToString(valueUnwrap(value))
private fun valueUnwrap(value: Any) = (value as? TypedId)?.id ?: value
}
fun <T: TypedId> Table.typedUuid(name: String, constructor: (UUID) -> T) = registerColumn<T>(name, TypedUUIDColumnType<T>(constructor))
fun <T: TypedId> Column<T>.autoGenerate(constructor: (UUID) -> T): Column<T> = clientDefault { constructor(UUID.randomUUID()) }
class StarWarsFilmId(id: UUID): TypedId(id)
object StarWarsFilms : Table() {
val id = typedUuid("id") { StarWarsFilmId(it) }.autoGenerate{ StarWarsFilmId(it) }
val name: Column<String> = varchar("name", 50)
val director: Column<String> = varchar("director", 50)
final override val primaryKey = PrimaryKey(id)
}
```
Reference: [#149](https://github.com/JetBrains/Exposed/issues/149)
### More questions on Stack Overflow:
https://stackoverflow.com/questions/tagged/kotlin-exposed
https://stackoverflow.com/questions/tagged/kotlin-exposed