Validating submission to avoid schedule conflicts

Chong-ho (Alex) Yu, Ph.D., MCSE, CNE


I created a webpage for users to register for a conference. In the form the users can select different seminars in the conference as the following:

Section A
Section B
Section C
Seminar 1: 9 am - 12 pm Seminar 2: 9 am - 12 pm Seminar 3: 9 am - 12 pm
Seminar 3: 1 pm - 5 pm Seminar 4: 1 pm - 5 pm Seminar 5: 1 pm - 5 pm
Seminar 6: 6 pm - 9 pm Seminar 7: 6 pm - 9 pm Seminar 8: 6 pm - 9 pm

Several seminars will be held at the same time. The server should reject the input if the selection leads to a schedule conflict.


I have experimented with several ways for this type of erroring checking. Before I tell you what can work, let me tell you what cannot work. Using IsEmpty function may not work properly. For example, you can set up a validation rule for the field Seminar 1 as "IsEmpty(Seminar 2) and IsEmpty(Seminar 3)" It works fine as long as the user does not go back to edit his record. If the user wants to cancel Seminar 2 and choose Seminar 1, he will not be allowed to do so because even if Seminar 2 is deselected, the field value is "blank" rather than "empty." ("Blank" is datum of nothing but "empty" is no datum at all) Also, in a web form even if the field is empty, it will be submitted as "blank."

The following is a better way:

	<input type=hidden name="Check morning"	value=1>
	<input type=hidden name="Check afternoon" value=1>
	<input type=hidden name="Check evening" value=1>

The same approach can be applied to more complicated scheduling.


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