Calculate previous day in ABAP CDS? - date

Question

I am starting with ABAP, I use the following instruction to obtain the date in the system but I can't get the date of the previous day, does anyone have any suggestions? THANKS.
I tried with:
{
$session.system_date as today,
$session.system_date - 1 as yesterday
}
but I can't do arithmetic operations with dates and it marks an error.

Answer 1

You can use DATS_ADD_DAYS function for this task.
It does not allow putting session vars directly as an argument, but we can do the following trick:
define view Z_TODAY
as select from
zsomething
{
key field1 as type1,
key field2 as type2,
...
$session.system_date as today,
DATS_ADD_DAYS( cast( $session.system_date as abap.dats ),-1,'NULL') as yesterday
}
Wrapping the system date into CAST does the thing.
Another, less intuitive way (which can be more flexible sometimes) is putting optional parameter with predefined value:
define view Z_TODAY
with parameters
#Environment.systemField : #SYSTEM_DATE
p_datum : abap.dats
as select from zsomething
{
key field1 as type1,
key field2 as type2,
...
$session.system_date as today,
DATS_ADD_DAYS( :p_datum,-1,'NULL') as yesterday
}