Comments on: override database and logical file

By: tomliotta

tomliotta — Fri, 02 Dec 2011 08:07:36 +0000

both operation retrieve record using Physical file access path, or different access path????

Neither. Those don’t retrieve records. They determine where records will be retrieved from.

OVRDBF determines that the records will be retrieved through an access path for the file named in the TOFILE() parameter. The file that is overridden to can be a different PF or it can be a LF over the original file or over a different PF. The file that is overridden from can be a PF or a LF.

The access path for an LF will be used to retrieve records when a LF is opened.

In both cases, the access path might be the same as a PF or different. Access paths can be ‘shared’ between files. It’s often best to arrange files so that access paths are shared. Any access path that is shared will necessarily always be over records from the same PF (or PFs, in the case of joins or unions such as a multi-format LF).

Tom

By: pdsathishkumar

pdsathishkumar — Fri, 02 Dec 2011 06:41:03 +0000

OVRDBF and LF, the both operation retrieve record using Physical file access path, or different access path????

By: tomliotta

tomliotta — Thu, 01 Dec 2011 20:48:39 +0000

why we can use both operation OVRDBF and LF….

Why not?

The two are different. They don’t do the same things; they don’t directly conflict with each other.

Tom

By: philpl1jb

philpl1jb — Thu, 01 Dec 2011 12:40:01 +0000

Yes both can be used. But you seem confused.

The OVRDBF is used to present a different file (or member) to the RPG program.

A logical file delivers the records in a different sequence and or by different selection rules.

The rpg program will generally fail if
- the file presented to it has a different structure (Recocd Format)
- the file presented has a different key structure and is used by the RPG program.
Phil

By: philpl1jb

philpl1jb — Tue, 29 Nov 2011 13:14:04 +0000

So many questions, so little time.
Have you done any research before you ask?
Phil

Add embedded SQL, embedded dynamic SQL, SQL views to the mix.
And consider OVRDBF with OPNQRYF

Organizational standards and simplicity and flexibility of code all go into the mix
Phil

By: deepu9321

deepu9321 — Tue, 29 Nov 2011 09:30:24 +0000

As Tom mentioned, Both OVRDBF & LF are having their own advantages,
If you would like to create a view in runtime, you can use OPNQRYF command.

Pradeep.

By: tomliotta

tomliotta — Tue, 29 Nov 2011 07:35:29 +0000

Neither has an advantage. They are two very different types of things used for different kinds of reasons.

OVRDBF allows you to substitute one file in place of another file at run-time.

Different LFs allow you to use different views or indexes over the same physical file usually at compile-time.

Tom