funcs_new.c

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/* src/tutorial/funcs_new.c */

/******************************************************************************
  These are user-defined functions that can be bound to a Postgres backend
  and called by Postgres to execute SQL functions of the same name.

  The calling format for these functions is defined by the CREATE FUNCTION
  SQL statement that binds them to the backend.

  NOTE: this file shows examples of "new style" function call conventions.
  See funcs.c for examples of "old style".
*****************************************************************************/

#include "postgres.h"           /* general Postgres declarations */

#include "executor/executor.h"  /* for GetAttributeByName() */
#include "utils/geo_decls.h"    /* for point type */


PG_MODULE_MAGIC;

/* These prototypes just prevent possible warnings from gcc. */

Datum       add_one(PG_FUNCTION_ARGS);
Datum       add_one_float8(PG_FUNCTION_ARGS);
Datum       makepoint(PG_FUNCTION_ARGS);
Datum       copytext(PG_FUNCTION_ARGS);
Datum       concat_text(PG_FUNCTION_ARGS);
Datum       c_overpaid(PG_FUNCTION_ARGS);


/* By Value */

PG_FUNCTION_INFO_V1(add_one);

Datum
add_one(PG_FUNCTION_ARGS)
{
    int32       arg = PG_GETARG_INT32(0);

    PG_RETURN_INT32(arg + 1);
}

/* By Reference, Fixed Length */

PG_FUNCTION_INFO_V1(add_one_float8);

Datum
add_one_float8(PG_FUNCTION_ARGS)
{
    /* The macros for FLOAT8 hide its pass-by-reference nature */
    float8      arg = PG_GETARG_FLOAT8(0);

    PG_RETURN_FLOAT8(arg + 1.0);
}

PG_FUNCTION_INFO_V1(makepoint);

Datum
makepoint(PG_FUNCTION_ARGS)
{
    Point      *pointx = PG_GETARG_POINT_P(0);
    Point      *pointy = PG_GETARG_POINT_P(1);
    Point      *new_point = (Point *) palloc(sizeof(Point));

    new_point->x = pointx->x;
    new_point->y = pointy->y;

    PG_RETURN_POINT_P(new_point);
}

/* By Reference, Variable Length */

PG_FUNCTION_INFO_V1(copytext);

Datum
copytext(PG_FUNCTION_ARGS)
{
    text       *t = PG_GETARG_TEXT_P(0);

    /*
     * VARSIZE is the total size of the struct in bytes.
     */
    text       *new_t = (text *) palloc(VARSIZE(t));

    SET_VARSIZE(new_t, VARSIZE(t));

    /*
     * VARDATA is a pointer to the data region of the struct.
     */
    memcpy((void *) VARDATA(new_t),     /* destination */
           (void *) VARDATA(t), /* source */
           VARSIZE(t) - VARHDRSZ);      /* how many bytes */
    PG_RETURN_TEXT_P(new_t);
}

PG_FUNCTION_INFO_V1(concat_text);

Datum
concat_text(PG_FUNCTION_ARGS)
{
    text       *arg1 = PG_GETARG_TEXT_P(0);
    text       *arg2 = PG_GETARG_TEXT_P(1);
    int32       arg1_size = VARSIZE(arg1) - VARHDRSZ;
    int32       arg2_size = VARSIZE(arg2) - VARHDRSZ;
    int32       new_text_size = arg1_size + arg2_size + VARHDRSZ;
    text       *new_text = (text *) palloc(new_text_size);

    SET_VARSIZE(new_text, new_text_size);
    memcpy(VARDATA(new_text), VARDATA(arg1), arg1_size);
    memcpy(VARDATA(new_text) + arg1_size, VARDATA(arg2), arg2_size);
    PG_RETURN_TEXT_P(new_text);
}

/* Composite types */

PG_FUNCTION_INFO_V1(c_overpaid);

Datum
c_overpaid(PG_FUNCTION_ARGS)
{
    HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER(0);
    int32       limit = PG_GETARG_INT32(1);
    bool        isnull;
    int32       salary;

    salary = DatumGetInt32(GetAttributeByName(t, "salary", &isnull));
    if (isnull)
        PG_RETURN_BOOL(false);

    /*
     * Alternatively, we might prefer to do PG_RETURN_NULL() for null salary
     */

    PG_RETURN_BOOL(salary > limit);
}