NanoSecond Timestamp values aren't converted into Generic mode

[ayushtkn]

Apache Iceberg version

main (development)

Query engine

None

Please describe the bug 🐞

While fetching the initial default values for columns of type nanosecond timestamp, Long is returned instead of the generic types.

The reason being:

iceberg/core/src/main/java/org/apache/iceberg/data/GenericDataUtil.java

Lines 38 to 58 in 15485f5

	public static Object internalToGeneric(Type type, Object value) {
	if (null == value) {
	return null;
	}
	switch (type.typeId()) {
	case DATE:
	return DateTimeUtil.dateFromDays((Integer) value);
	case TIME:
	return DateTimeUtil.timeFromMicros((Long) value);
	case TIMESTAMP:
	if (((Types.TimestampType) type).shouldAdjustToUTC()) {
	return DateTimeUtil.timestamptzFromMicros((Long) value);
	} else {
	return DateTimeUtil.timestampFromMicros((Long) value);
	}
	case FIXED:
	return ByteBuffers.toByteArray((ByteBuffer) value);
	}
	return value;

The internalToGeneric method only handles TIMESTAMP not the TIMESTAMP_NANO

Willingness to contribute

• I can contribute a fix for this bug independently
• I would be willing to contribute a fix for this bug with guidance from the Iceberg community
• I cannot contribute a fix for this bug at this time