--The code below, in a nutshell, captures cases where the user may change the date inappropriately (if not null out the field)
	and provides some validation error if not gives you the "YYYY-MM-DD" format as intended. Use this in your saveInto for the value--

if(
  or(
    rule!APN_isBlank(ri!date),
    len(year(ri!date)) <> 4,
    and(
      or(
        month(ri!date) = 10,
        month(ri!date) = 11,
        month(ri!date) = 12
      ),
      len(month(ri!date)) <> 2
    ),
    and(
      or(
        month(ri!date) = 1,
        month(ri!date) = 2,
        month(ri!date) = 3,
        month(ri!date) = 4,
        month(ri!date) = 5,
        month(ri!date) = 6,
        month(ri!date) = 7,
        month(ri!date) = 8,
        month(ri!date) = 9
      ),
      len(month(ri!date)) <> 1
    ),
    and(
      len(day(ri!date)) <> 1,
      len(day(ri!date)) <> 2
    )
  ),null,
tostring(
year(ri!date)&"-"&
if(len(month(ri!date))=1,
"0"&month(ri!date),
month(ri!date)
)
&"-"&
if(len(day(ri!date))=1,
"0"&day(ri!date),
day(ri!date)
)
))