I've got a task, to calculate end date of validity period for an object.
Let's say start date of validity is: 18 Sept. 2014
Validity period (for example) is: 3 months
End date (last date when object is still valid, + 3 months and -1 day): 17 Dec 2014
Looks correct, and to calcuate end date I used the following @-formula:
@Adjust(start; 0; 3; -1; 0; 0; 0);
where I add 3 months and decrease 1 day from the start date.
But when I set start date as 01 Oct. 2014 I get end date 30 Dec 2014 instead of 31 Dec 2014.
Looks strange and looks like a bug in the Lotus Notes engine.
The solution was a bit unexpected and simple.
@Adjust function evaluates it's parameters from right to left.
In other words it decreases 1 day and then adds 3 months to the start date.
And if start date is 01 Oct 2014, then @Adjust formula gets 30 Sept. 2014 by adding -1 day and then adds 3 months and get 30 Dec 2014.
And to solve this issue I needed to change the initial formula:
to
temp_ := @Adjust(start; 0; 3; 0; 0; 0; 0);
@Adjust(temp_; 0; 0; -1; 0; 0; 0);
temp_ variable gets start date increased to 3 months, and only after that we decrease 1 day from the calculation result.