[FEATURE REQUEST] ClickHouseValue return ClickHouseValue data for nested types

[pan3793]

e.g. for array type

interface ClickHouseValue {
  Object[] asArray()
  <T> T[] asArray(Class<T> clazz)

  // wanted
  ClickHouseValue[] asArrayValues()
}

[zhicwu]

Thanks for the suggestion @pan3793. I think you can use ClickHouseArraySequence(sub-interface of ClickHouseValue just for wrapping array values), which was added in PR #1087:

ClickHouseColumn column = ClickHouseColumn.of("", "Array(Int8)");
ClickHouseArraySequence array = ClickHouseValues.newArrayValue(column);
ClickHouseValue nestedValue = ClickHouseValues.newValue(config, column.getNestedColumns().get(0));
for (int i = 0, len = array.length(); i<len; i++) {
  System.out.println(array.getValue(i, nestedValue).asObject());
}

Although the method you suggested is easier to use, I'd suggest to go with above painful approach. The major concern here is memory usage. ClickHouseValue is designed as a container object mainly for ease of type conversion. In most cases, we should reuse one single instance for all values of a column for serialization/deserialization, instead of multiple instances one for each value, or the memory usage will be too high(try compare ClickHouseByteValue and byte), and the overall performance will be decreased.

[pan3793]

Thanks for the quick reply, I think we should provide such API in ClickHouseValue and add warnings about performance and resources in Javadoc.

[zhicwu]

I had a rough idea of moving ClickHouseValues.new*Value methods to ClickHouseColumn for ease of use and slightly improved performance. Maybe it's better to rename ClickHouseArraySequence to ClickHouseIterableValue to cover all nested types, along with new methods ClickHouseValue[] copyValues(ClickHouseColumn) and ClickHouseValue[] getValues(ClickHouseValue[]) for convenience.