Re: Using PF constraints

["Carel Teijgeler" <coteijgeler@xxxxxxxxx>]

Martin,

I have done some deleting old records using constraints. I use the cascading 
method to get a "waterfall" delete: delete one master record and all depending 
children are "automatically" removed as well.

Some considerations, any way:
1) Journalling is required.
2) Duplicate keys are not allowed.
3) Orphaned records (details without master record) are not allowed (solved 
this using SQL to remove those records)
4) You can only link master to detail (parent to child), not the other way 
around (although that may be handy sometimes).
5) If the main PF is keyed, you may accidently remove the access path when 
removing the constraint.

An example to illustrate this.

An example that works:
File A (master) primary key: OrdernumberA  
          File B(child) primary key: OrdernumberA-OrderLineA
          File C (master) foreign key: OrdernumberA 
                                primary key: OrdernumberB
                    File D (child) primary key: OrdernumberB-OrderlineB

Constraint File A - File B: OrdernumberA
                File A - File C: OrdernumberA
                File C - File D: OrdernumberB

When deleting a record from File A, all child records with the same ordernumber 
in File  B were deleted. Because a constraint was made from File A to File C, 
all records in File C with the same ordernumberA from File A were also removed 
and a consequence of that records from File D were removed.

Regards,
Carel Teijgeler



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On 29-4-03 at 15:37 Saunders, Martin P wrote:

>I am canvassing for opinions on using ADDPFCST to effect data purges instead 
>of writing (comparatively) more complex RPG >programs to perform this 
>function.  The way I see it, if we add the appropriate constraint to a detail 
>file which has an associated >header file with a primary key and specify 
>'cascading delete', deleting records from the header file willautomatically 
>zap the >associated detail records right?
>
>Is there a good reason why I've never seen this being used?  Or is it just the 
>shops that I've worked with that do not think this is a >useful feature?