dataframe-jdbc/org.jetbrains.kotlinx.dataframe.io.db/Sqlite/Companion/withCustomConverters

withCustomConverters

fun withCustomConverters(block: SqliteCustomConvertersBuilder.() -> Unit): Sqlite

Builds a Sqlite with custom type converters registered via a SqliteCustomConvertersBuilder DSL block.

use forType to register a converter keyed by the declared SQL type name (as written in CREATE TABLE);
use forColumn to register a converter keyed by column name (takes precedence over forType for the named column).

Both DSL functions accept two generic type parameters:

T — the storage class of the raw stored value String, Int, Long, Double, or ByteArray or their nullable variants).
R — the target Kotlin type of the resulting DataFrame column; must be reified.

The converting lambda receives the raw value and returns the converted result;

Example

val format = LocalDateTime.Format {
    year(); char('-'); monthNumber(); char('-'); day()
    char(' ')
    hour(); char(':'); minute(); char(':'); second()
    chars(" UTC")
}

val sqlite = Sqlite.withCustomConverters {
    // Parse a custom text representation into Instant.
    forType("MY_DATETIME") { raw: String? ->
        raw?.let { LocalDateTime.parse(it, format).toInstant(TimeZone.UTC) }
    }

    // Explicitly treat values columns with of `LONGVARCHAR` type as nullable strings.
    // This is necessary because SQLite type affinity assigns those columns the `NUMERIC`
    // base type, causing DataFrame to expect integer values.
    // No conversion is performed; only the expected value type is specified.
    forType<String?>("LONGVARCHAR")

    // Override conversion for a specific "time" column.
    // Column-specific converters take precedence over type-specific converters.
    forColumn("time") { raw: String -> raw.toDouble() }
}

val df = DataFrame.readSqlTable(connection, "events", dbType = sqlite)