I have 3 tables that make up a class registration system. I have classes,
sections, and enrollments. One class has many sections. One section has
many enrollments. Actually, there's a 4th table: customers. An enrollment
is linked to both a section and a customer.

Classes table has a single primary key: classid. Sections has a 2-part
primary key: classid and sectionid. Classid is also a foreign key, which
references the classes table's primary key. Enrollments has a 3-part
primary key: classid, sectionid, and enrollid. Classid and sectionid also
make up a foreign key which references the sections table's primary
key. Enrollments also has another foreign key: customerid, which
references the customer table's primary key.

Ok. In my app, I have a classes screen and a sections screen. On the
classes screen, I have a TIBOTable for the Classes table. On the screen, I
show the classes fields, and I have a TDBGrid which shows the sections for
that class. I also have a button to add a new section for the current
class. On the sections screen, I have a TIBOTable for the Sections table,
and I also have a TDBGrid showing all the enrollments. (Both grids are
attached to separate TIBOTable objects, set up with the proper
master-detail properties.

When the user is on the classes screen and clicks the "add new section"
button, I switch to the sections screen, and do an Append() on the sections
table. The table's OnNewRecord event fills in the section's classid field
with the classid of the current class. It grabs the next available
sectionid for that class, and fills that in as well. It then leaves the
record open for the user to fill in the rest of the Section fields. There
is a TDBNavigator on the screen, so when the user is done filling in the
fields, they click the check mark to save the record.

All this works beautifully almost all the time. But, I've recently had two
different customers complain that once in a while on certain classes, when
they click the "add new section" button, the new section comes up with
customers already enrolled in it! This did not seem possible to me, given
the key structure that I have set up, so I had one of them go through it
with me on the phone. Here's what we observed:

Go to the class and click on Add New Section.
Section #16 is added, but it's enrollment grid is already populated with 5
customers.
Click on the checkmark to save the section. The record (section #16) is
posted successfully.
Go back to the Classes tab (same class), and click Add New Section again.
Section #17 is added, and it's enrollment grid is already populated with
the same 5 customers.
Click on the checkmark to save the section. The record (section #17) is
posted successfully.
Repeat two more times for sections 18 and 19.
Go back and check all 4 sections. They ALL have the SAME 5 students in
them!?!?!?

This does not seem possible, given my key structure. The enrollment grid's
table's master-detail relationship is based on the section's classid and
sectionid. If these are all the same enrollment records on each section,
they should only be able to link to ONE section, yet each section has a
different sectionid. But there they are.

I had the user exit my app and go back it. We found that all 4 sections
were still there, but the "phantom" enrollments were all gone from the
grid, as they should be.

The customer was happy with that, but I promised that I would get to the
bottom of why it happened. I can't figure it out. As I said, it has
happened to another customer of mine as well, so I need to get it fixed.

Any ideas?

-Joe