RE: CHAIN Versus SETLL and READ When Data Needed

[Arjen Drieënhuizen <Arjen.Drieenhuizen@xxxxxxxxx>]

I agree, I did run into some strange situations with non-unique keys and
CHAIN, is it the oldest or the newest record that gets read first, and does
it leave the other records with the same key untouched?? While by
SETLL/SETGT this isn't an issue.


Just a thought

Arjen

-----Oorspronkelijk bericht-----
Van: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
Namens Forbes, Vincent
Verzonden: woensdag 28 februari 2007 20:51
Aan: RPG programming on the AS400 / iSeries
Onderwerp: RE: CHAIN Versus SETLL and READ When Data Needed

My vote is "it depends".  I would use the chain if key1 was a unique key.  

I would use the setll/reade with a do loop if it was a partial key or if I
was going to use key2.  Or Fld3 could have either *hival or *loval.


\Vincent


I posed this question on MCPressOnline the other day but I would like to
get more opinions on it so I'll post it here too.   A shop-standard
hangs in the balance.

 

   Assume that you have an RPG program that has logic such that you need to
first see if some data is in a file, based on a key, and then if so, you do
something with that data.

 

   Further assume that this file has a complex key with three fields.   

 

    The program logic is such that you check the maximum number of keys for
a match down to the minimum number of keys

 

     Like this:

 

              Key1    Klist

                          Kfld              Fld1

                          Kfld              Fld2

                          Kfld              Fld3

 

              Key2     Klist

                          Kfld              Fld1

                          Kfld              Fld2

 

              Key3     Klist

                           Kfld             Fld1

 

 

   Which one of these logic blocks is most efficient?

 

   Key1   Setll   file

       If    %FOUND(file)

               Key1   READE file

                       Use Fields

       Else

          Key2    Setll  File

            If   %FOUND(file)

                     Key2 Use Fields

           Else

             Key3  Setll File

                  If   %FOUND(file)

                     Key3 READE file

               Endif

            Endif

          Endif

                  

 

 

OR....

 

               KEY1  Chain file

                          If       %FOUND(file)

                              Use fields

                         Else

              KEY2   Chain  file

                          If      %FOUND(file)

                              Use Fields

                          Else

              KEY3   Chain file

                          If   %FOUND(file)

                             Use Fields

                         Endif

                         Endif

                         Endif

 

 

My opinion is that the CHAIN is more efficient from both a
coding/maintenance standpoint and from an I/O standpoint, but I'm open to
opinions.

 

 

 

 

 

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