IIF Expression in RDLC report of ASP.NET project acting weird

Question

I'm working on a ASP.NET project where I'm using RDLC report to generate reports. In a report in some field I'm using an expression like below:

=IIf(Fields!Day.Value >= 1 And Fields!Day.Value <= 7, WeekdayName(Fields!Day.Value), "invalid")

The problem is, If the value is between 1 to 7, it's working fine, but if the value is 0 it's printing #Error, which is unexpected. But If my expression is like below:

=IIf(Fields!Day.Value >= 1 And Fields!Day.Value <= 7, "True", "invalid")

Then, it works as expected, it printing invalid for value=0. Can someome point me out the issue?

Answer 1

The problem is the WEEKDAYNAME() function is being evaluated even if the weekday is out of range, hence the error.

You can fix it by passing a valid value to 'WEEKDAYNAME()' when it's an invalid value, this will never be returned but satisfies the function.

Change the exression to this and it will work

=IIF(
    Fields!Day.Value >= 1 And Fields!Day.Value <= 7, 
    WEEKDAYNAME(
        IIF(Fields!Day.Value >=1 AND Fields!Day.Value <=7, Fields!Day.Value, 1)
        )
    , "invalid"
    )