Group by with a JSON field

[antham]

Question

How it is possible to generate a group by statement related to a JSON field?
For an order by we get the sqljson package and we can do something like Order(sqljson.OrderValue(article.FieldMetadata, sqljson.Path("tag"))), considering metadata is a JSON object with a tagkey.
For the GroupBy I don't see how to do that easily, the only thing easy to do is to provide the whole field like that GroupBy(article.FieldMetadata).