Function partition_key_columns 

pub fn partition_key_columns(
    rel: &Relation,
    session: &dyn Session,
) -> Result<String>

pg_get_partkeydef_columns(oid, true): the columns and the expressions of the partition key of a partitioned table, with no strategy, collations or operator classes, as the detail of an error of tuple routing shows them.

Errors

The error of the deparse of an expression of the key.