Ubuntu Manpage: PQspecPrepare - Prepares a libpqtypes specifier format string.

Provided by: libpqtypes-dev_1.5.1-2_amd64

NAME

       PQspecPrepare - Prepares a libpqtypes specifier format string.

SYNOPSIS

       #include <libpqtypes.h>

       int PQspecPrepare(PGconn *conn, const char *name,
                             const char *format, int is_stmt);
       void PQclearSpecs(PGconn *conn);

DESCRIPTION

PQspecPrepare allows an application to prepare specifier format strings that will be used frequently. By
preparing a specifier format string, one avoids the parsing and type handler lookup costs. This becomes
a significant win when managing large result sets or arrays, where the specifier format, like "%int4
%text %bytea", must be prepared for each tuple/element.

As with PQregisterXXX, only specifier format strings prepared prior to the creation of a PGresult or
PGparam, will be available for use. This is because the prepared type spec is cached within a PGconn
object and copied to all subsequent PGparam and PGresult objects.

Every prepared type spec is given a name, which is used as its unique identifier. To use a prepared type
spec, the name is provided where ever a regular specifier format string is allowed, like PQputf or
PQgetf. The name must be proceeded by a ´@´ AT sign. For more information about the syntax, see the
pqt-specs(3) man page.

The format argument is the specifier format string being prepared. When this is NULL, the name prepared
type spec is removed from the PGconn´s internal array.

The is_stmt argument indicates if a parementerized statement version of format should be cached along
with the prepared type spec. This means all type specifiers in format, like "%int4", will be converted
to "$1" syntax. When is_stmt is non-zero, a statement will created and cached. For more information on
specifer format string to paremterized statements, see the PQputf(3) man page. NOTE: to use a prepared
type spec with execution functions like PQexecf, is_stmt must be set to non-zero.

PQclearSpecs removes all prepared specifiers from the given PGconn, as opposed to removing them one by
one by setting PQspecPrepare's format argument to NULL. A good use for this is after a PQresetXXX call
when it might be desired to re-prepare all type specifiers.

Functions that support the use of a prepared type spec are: PQputf, PQputvf, PQgetf, PQgetvf, PQexecf,
PQexecvf, PQsendf, PQsendvf, PQparamExec, PQparamSendQuery.

HINT: A good rule of thumb for using prepared type specs, is when there are a large number of
PQputf/PQgetf calls per statement execution. This commonly occurs when dealing with large result sets
and arrays.

RETURN VALUE

       PQspecPrepare  and PQclearSpecs return a nonzero value on success and zero if it fails.  Use PQgeterror()
       to get an error message.

EXAMPLES

       This example prepares a type spec and issues some PQputf calls.

              int i;
              PQparam *param;

              if(!PQspecPrepare(conn, "prepared_spec", "%int4 %text", 0))
              {
                   fprintf(stderr, "PQspecPrepare: %s0, PQgeterror());
                   exit(1);
              }

              /* create after preparing spec */
              param = PQparamCreate(conn);

              for(i=0; i < 100000; i++)
              {
                   /* NOTE: nothing else can be in format string */
                   PQputf(param, "@prepared_spec", 4, "text");
              }

              /* This elects to prepare a statement as well.  After this returns,
               * "SELECT myfunc($1, $2)" will be cached along with the prepared spec.
               */
              PQspecPrepare(conn, "myfunc", "SELECT myfunc(%int4, %text)", 1);

              /* "myfunc" tells execf to execute "SELECT myfunc($1, $2)".  If is_stmt
               * was set to zero during the PQspecPrepare, the below would be invalid
               * because execf doesn't know what to execute.
               */
              PQexecf(conn, "@myfunc", 123, "text");

              /* clear'm all */
              PQclearSpecs(conn);

RATIONALE

       None.

AUTHOR

       A contribution of eSilo, LLC. for the PostgreSQL Database Management System.  Written by Andrew Chernow.

REPORTING BUGS

       Report bugs to <libpqtypes@esilo.com>.

COPYRIGHT

       Copyright (c) 2011 eSilo, LLC. All rights reserved.
       This is free software; see the source for copying  conditions.   There  is  NO  warranty;  not  even  for
       MERCHANTABILITY or  FITNESS FOR A PARTICULAR PURPOSE.