Re: PL/PGSQL: Dynamic Record Introspection

good idea. it's what can eliminate not neccessery using plperl. I would to
see it in plpgsql.

regards
Pavel

On Thu, 14 Jul 2005, Titus von Boxberg wrote:

> Hi all,
>
> I needed introspection capabilities for record types to write more generic
> trigger procedures in PL/PGSQL.
>
> With the following patch it's possible to
> - extract all field names of a record into an array
> - extract field count of a record
> - address a single field of a record with a variable
>    containing the field name (additional to the usual record.fieldname
>    notation where the fieldname is hardcoded).
>
> The syntax is
> - record%NFIELDS gives the number of fields in the record
> - record%FIELDNAMES gives the array of the field names
> - record%scalarvariable extracts the field whose name
>    is equal to the contents of scalarvariable
>
> ------------
>
> The patch is nonintrusive in the sense that it only adds things
> with one exception:
> In function exec_eval_datum(), file pl_exec.c, line 3557 (after the patch)
> I chose to convert the record field values to TEXT if the caller does
> not require a certain type (expectedtypeid == InvalidOid).
> Additionally, I cast the value from the record field type if
> the destination Datum is of different type.
>
> As far as I can see, this does no harm because in most cases
> the expectedtypeid is correctly set. I just wanted to avoid that
> if it is not set, the returned datum is of a more restrictive type
> than TEXT.
>
> ------------
>
> The patch is against a HEAD checkout from 07/12/05
> The output comes from difforig.
>
> Test code for the patch can be extracted from an example I put into
> plpgsql.sgml
>
> ------------
>
> Here is a summary of things that get patched by the file:
> - add three new special parsing functions to pl_comp.c
>    (plpgsql_parse_wordpercentword, plpgsql_parse_wordnfields,
>    plpgsql_parse_wordfieldnames).
> - modify PLpgSQL_recfield in plpgsql.h to either hold
>    a conventional field name (record.fieldname) or a dno
>    for the variable (record%variable).
> - add two PLPGSQL_DTYPEs for the two new % notations
> - modify "case PLPGSQL_DTYPE_RECFIELD:"
>    in exec_eval_datum() and exec_assign_value()
>    to deal with index strings from a variable
> - add "case PLPGSQL_DTYPE_RECFIELDNAMES"
>    and "case PLPGSQL_DTYPE_NRECFIELD"
>    to exec_eval_datum() to evaluate  %FIELDNAMES
>    and %NFIELDS expressions.
> - update plpgsql.sgml in the docs directory
>
> ------------
>
> Please notify me if I can be of further assistance.
>
> Regards
> Titus
>