in druid 26, is it possible to convert array to multi value dimension in an expression ? Something like this, but array_to_mv was introduced in a later version of druid.

{
  "type": "expression",
  "name": "details",
  "expression": "array_to_mv(details_array)"
}

any specific reason to do so? Arrays are far more consistent in their handling and a lot easier to reason about. If you wanna do it for how the group by is handled, it would be far easier to switch to a version supporting UNNEST and using that

It is a dimension from a datasource created several years ago(druid 0.12). And i need to add a transformation now. I dont want to change the type of the dimension now.

with ingest time transforms you should be able to input arrays from a transform to a string dimension