Classic Master Detail form problem

[sbasak]

This is a classic problem. I have two tables (master detail). When in detail table I insert the product quantity a trigger is there in database which populates Price columns. I have generated the form using Data Form Wizard.

Transaction
-----------
TNo
Customer
Date
Total

Details
-------
TNo
DtlNo
ProductCode
Quantity
Price




**********************************************
--------------------------------------------
[Load] [Cancel All] [Update]
---------------------------------------------
TNo 500
Customer J. Smith
Date 2003-09-25
Total
----------------------------------------------
DtlNo ProductCode Quantity Price
----------------------------------------------
100 1256879 1 100
101 1356897 2 50
102 1356878 2 200

----------------------------------------------
**********************************************


Now here are the problems

[1] The master records has to be saved first before inserting detail records. If I don't save the master record first, child record can't be inserted. So, I have to insert a master record, click on Update, and then start inserting detail records.

How can I overcome double saving concept?

[2] There is a stored procedure in database, which returns the total sales amount if a particular "TNo" is passed as input. I want that when I click the update button all the following actions should happen -
* Both master and detail records are saved
* The total amount value is populated and saved. I know how to call a stored procedure in VB.NET, however, I am confused where I should call the procedure so that it populates the date just before saving the data.

Thanks for any help. I think some you must have solved this. So, I shall be glad to know your approach.