Programatically Assigning Column Value Based on Another Column

Question

I have a problem as follows:
My database table has the following setup:
There may be many gift numbers the same, however many different recipient numbers for each gift.
The receipient number should increment from 1-X based on the gift number, for example, if the gift number is the same then the receipient number should increment for that gift.
Gift Number
Recipient Number
1
1
1
2
1
3
2
1
3
1
3
2
The programmatic code for inserting a new row would be:
Check if gift number already exsists in database.
-if it does exsist then find latest and increment current receipient number by one for receipment number
-if it does not exsit set receipient number at 1
How do i do this?
JDEV - 11.1.2.4 (ADF BC)

Answer 1

Your use case has some flaws which you should think about before trying to implement it.
1) think about what happens if multiple users try to insert a record at the same time. What can happen? How do you want to handle this situation?
2) do you really need the number to be gap less? The use case can be implemented easily if you don't have this restriction.
3) The table should have the technical primary key to avoid pk clashes due to multiple inserts at one time.
Now, if you have a technical pk as primary key, you can setup a unique key on both of the other columns which prevents that somehow you get duplicates there.
You let the user insert the gift number and calculate the recipient number as max(recipient number)+1. Then you commit the record. If you don't get an error you are finished, if you get an error you add 1 to the recipient number and try to commit again, until the insert works.
Timo