Addressing set's child table

[whanigsberg]

Hi everybody,

I am trying and failing at something simple.

I have a very simple set (it is a demo, really) consisting of a teacher table linked 1:1 to a courses table. The set is called "workload.set".

I open it:

tbl = table.open("workload.set")

and I want to read the value of a field ("no_stud" that is, number of students) which is contained in the child table. In fact, the only reason for this set is to allow me to query on teacher ID in the parent and read the values of the courses he teaches.

The query works fine and gives me my small number of records and I want to fetch through them and add up the number of students. (I'll also have to do a few more things but this one shows the problem.)

The line
vNStuds_total = vNStuds_total+tbl.no_std
gets me a subelement not found error for tbl.no_std.

So the question is how do I address a field in the child table of a one to one set?

Thanks,
Bill

[Peter.Wayne]

RE: Addressing set's child table

this should work:


courses=table.get("courses.dbf")

vNStuds_total = vNStuds_total+courses.no_std

[crimmelcp]

RE: Addressing set's child table

William:
sometimes when I need to get record info from a set I use.

instead of tbl = table.open("workload.set")
I use t1 and t2 to reference the info
t1=table.current(1)

t2=table.current(2)
t2.fetch_first()
while .not. t2.fetch_eof()
if t2.service_Repair_ID=var->serviceid
t2.change_begin()
t2.service_Repair_ID=var->serviceid
t2.invoice_date=var->invdate
t2.vehicle_id=var->vehicleid
t2.last_name=var->lastname
t2.First_Name=var->firstname
t2.change_end()
end if
t2.fetch_next()
end while
Charlie Crimmel

[whanigsberg]

RE: Addressing set's child table

Thank you both for the quick reply.

The minute I let myself think about the problem it seemed likely that I needed a pointer to the child table. Somehow I had allowed myself to assume that in a 1:1 set a pointer to the set would give access to fields in both tables but no go on that.

I had started with the table_get method and in fact that works. So tbl2 became my pointer to the child. Now here is something convenient. I had run a query on the set which yielded 10 records. As I fetched through the parent table
tbl.fetch_next()
I did *not* have to move the record pointer to the child. I needed only
tbl2.no_stud
to get my value.

I hope this is the correct way to go about this.

Charlie, if I understand your code correctly you have a one to many relationship and are fetching through multiple child records for the same parent which is not exactly my situation. Also, table current doesn't work right (in my experience, anyway) from a script so I think your code is designed to run from a form object. Hence, I stuck with table_get.

The calculation I am trying to set up is really very nasty, even on a spreadsheet. It requires knowledge of properties of a group of records (e.g. total students, total class preparations) before you can calculate a value for any single record. So I must run 2 queries to get the group properties and then loop through the output of the second query to calculate the individual records.

The reason for enduring this nightmare is to dynamically show department chairs what happens to teachers' workloads as they add and remove courses from them.

Thanks again to you both.

Bill