Re: Howto use fields "by name"

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hello Antonio,

> If, in a RPG pgm, I manage to have in a field (let's call it FieldName)
> the name of a real field from an externally described file, and in
> another field, call it "FieldValue", a value (either alfa or numeric),
> is there a way to write something as:
> Eval FieldName(??) = FieldValue

It's relatively easy to get a list of fields in an externally defined
file, and their positions in a record.

It's possible to use the ILE C record i/o functions to read/write/update a
database without knowing any of the details of the database at compile
time.  And thanks to the design of the ILE environment, it's possible to
use these ILE C routines from an ILE RPG program.

But you've still got the task of taking generic data and reformatting it
to fit exactly the right way into the record buffer.

For example, if you've got a field called "FieldValue" what's in it?
Most likely, it's going to be an alphanumeric field with data formatted in
a human-readable format, because that allows it to be used for any
possible scenario.  Then, you've got to write routines that convert from
that human-readable format to the specific format, binary, packed, date,
time, timestamp, etc. that the database field is in.  And you have to be
able to do that based on the ability to look the fieldname up in the
external definition at run-time.

If FieldName is "Amount" and "FieldValue" contains "123.45", what do you
need to do?  You need to call an API to get the list of fields for the
database, scan through it for a field called "Amount".  Now you can find
out that "Amount" is an "11P 2" field in the database, so you have to
convert "123.45" to x'00000012345F' and store it into the record buffer at
the right position, and then save the record back to disk.

Is that possible?  Sure.  Is it easy?  No.  Remember, you know nothing
about the data at compile time -- so it's not easy at all.

There are some MI functions that can assist with this -- most notably
_LBCPYNV which will convert a numeric value from one format to another
based on pointers in memory.  That way, you can use a routine like %DEC()
to convert the character string to a very large (maybe 30P 9) numeric
field, and use _LBCPYNV to convert it to the correct field, copy that into
the record buffer, and then save the data.

Carsten Flensburg did a sample of parsing external record buffers in one
of his "APIs by Example" columns in my newsletter.  You can read it at the
following link (requires a free membership to the iSeries Network):

http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=17380