lo.c

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/*
 *  PostgreSQL definitions for managed Large Objects.
 *
 *  contrib/lo/lo.c
 *
 */
 
#include "postgres.h"
 
#include "commands/trigger.h"
#include "executor/spi.h"
#include "utils/fmgrprotos.h"
#include "utils/rel.h"
 
PG_MODULE_MAGIC_EXT(
                    .name = "lo",
                    .version = PG_VERSION
);
 
 
/*
 * This is the trigger that protects us from orphaned large objects
 */
PG_FUNCTION_INFO_V1(lo_manage);
 
Datum
lo_manage(PG_FUNCTION_ARGS)
{
    TriggerData *trigdata = (TriggerData *) fcinfo->context;
    int         attnum;         /* attribute number to monitor  */
    char      **args;           /* Args containing attr name    */
    TupleDesc   tupdesc;        /* Tuple Descriptor             */
    HeapTuple   rettuple;       /* Tuple to be returned         */
    bool        isdelete;       /* are we deleting?             */
    HeapTuple   newtuple;       /* The new value for tuple      */
    HeapTuple   trigtuple;      /* The original value of tuple  */
 
    if (!CALLED_AS_TRIGGER(fcinfo)) /* internal error */
        elog(ERROR, "lo_manage: not fired by trigger manager");
 
    if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event)) /* internal error */
        elog(ERROR, "%s: must be fired for row",
             trigdata->tg_trigger->tgname);
 
    /*
     * Fetch some values from trigdata
     */
    newtuple = trigdata->tg_newtuple;
    trigtuple = trigdata->tg_trigtuple;
    tupdesc = trigdata->tg_relation->rd_att;
    args = trigdata->tg_trigger->tgargs;
 
    if (args == NULL)           /* internal error */
        elog(ERROR, "%s: no column name provided in the trigger definition",
             trigdata->tg_trigger->tgname);
 
    /* tuple to return to Executor */
    if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
        rettuple = newtuple;
    else
        rettuple = trigtuple;
 
    /* Are we deleting the row? */
    isdelete = TRIGGER_FIRED_BY_DELETE(trigdata->tg_event);
 
    /* Get the column we're interested in */
    attnum = SPI_fnumber(tupdesc, args[0]);
 
    if (attnum <= 0)
        elog(ERROR, "%s: column \"%s\" does not exist",
             trigdata->tg_trigger->tgname, args[0]);
 
    /*
     * Handle updates
     *
     * Here, if the value of the monitored attribute changes, then the large
     * object associated with the original value is unlinked.
     */
    if (newtuple != NULL &&
        bms_is_member(attnum - FirstLowInvalidHeapAttributeNumber, trigdata->tg_updatedcols))
    {
        char       *orig = SPI_getvalue(trigtuple, tupdesc, attnum);
        char       *newv = SPI_getvalue(newtuple, tupdesc, attnum);
 
        if (orig != NULL && (newv == NULL || strcmp(orig, newv) != 0))
            DirectFunctionCall1(be_lo_unlink,
                                ObjectIdGetDatum(atooid(orig)));
 
        if (newv)
            pfree(newv);
        if (orig)
            pfree(orig);
    }
 
    /*
     * Handle deleting of rows
     *
     * Here, we unlink the large object associated with the managed attribute
     */
    if (isdelete)
    {
        char       *orig = SPI_getvalue(trigtuple, tupdesc, attnum);
 
        if (orig != NULL)
        {
            DirectFunctionCall1(be_lo_unlink,
                                ObjectIdGetDatum(atooid(orig)));
 
            pfree(orig);
        }
    }
 
    return PointerGetDatum(rettuple);
}