Partition and Functions

Hi Everyone,
I have a partitioned by period table scenario here where I need to
execute a query with a function in where clause.

I'm not sure if this is the best approach to do that, but when I use the
functions, it scans all the tables instead only the desired one. If I put
the parameter hardcoded, it works fine.

Any idea how could I solve this? Follow my query example:

SELECT customer_id,
date_id,
kpi AS kpi_value
FROM schema1.table1
WHERE date_id >= *To_char*(( current_date - interval '30' day ) :: DATE,
'YYYYMMDD')::INTEGER

Thanks!
Leandro Guimarães