tupconvert.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * tupconvert.c
 *    Tuple conversion support.
 *
 * These functions provide conversion between rowtypes that are logically
 * equivalent but might have columns in a different order or different sets of
 * dropped columns.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/common/tupconvert.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/tupconvert.h"
#include "executor/tuptable.h"


/*
 * The conversion setup routines have the following common API:
 *
 * The setup routine checks using attmap.c whether the given source and
 * destination tuple descriptors are logically compatible.  If not, it throws
 * an error.  If so, it returns NULL if they are physically compatible (ie, no
 * conversion is needed), else a TupleConversionMap that can be used by
 * execute_attr_map_tuple or execute_attr_map_slot to perform the conversion.
 *
 * The TupleConversionMap, if needed, is palloc'd in the caller's memory
 * context.  Also, the given tuple descriptors are referenced by the map,
 * so they must survive as long as the map is needed.
 *
 * The caller must supply a suitable primary error message to be used if
 * a compatibility error is thrown.  Recommended coding practice is to use
 * gettext_noop() on this string, so that it is translatable but won't
 * actually be translated unless the error gets thrown.
 *
 *
 * Implementation notes:
 *
 * The key component of a TupleConversionMap is an attrMap[] array with
 * one entry per output column.  This entry contains the 1-based index of
 * the corresponding input column, or zero to force a NULL value (for
 * a dropped output column).  The TupleConversionMap also contains workspace
 * arrays.
 */


/*
 * Set up for tuple conversion, matching input and output columns by
 * position.  (Dropped columns are ignored in both input and output.)
 */
TupleConversionMap *
convert_tuples_by_position(TupleDesc indesc,
                           TupleDesc outdesc,
                           const char *msg)
{
    TupleConversionMap *map;
    int         n;
    AttrMap    *attrMap;

    /* Verify compatibility and prepare attribute-number map */
    attrMap = build_attrmap_by_position(indesc, outdesc, msg);

    if (attrMap == NULL)
    {
        /* runtime conversion is not needed */
        return NULL;
    }

    /* Prepare the map structure */
    map = (TupleConversionMap *) palloc(sizeof(TupleConversionMap));
    map->indesc = indesc;
    map->outdesc = outdesc;
    map->attrMap = attrMap;
    /* preallocate workspace for Datum arrays */
    n = outdesc->natts + 1;     /* +1 for NULL */
    map->outvalues = (Datum *) palloc(n * sizeof(Datum));
    map->outisnull = (bool *) palloc(n * sizeof(bool));
    n = indesc->natts + 1;      /* +1 for NULL */
    map->invalues = (Datum *) palloc(n * sizeof(Datum));
    map->inisnull = (bool *) palloc(n * sizeof(bool));
    map->invalues[0] = (Datum) 0;   /* set up the NULL entry */
    map->inisnull[0] = true;

    return map;
}

/*
 * Set up for tuple conversion, matching input and output columns by name.
 * (Dropped columns are ignored in both input and output.)  This is intended
 * for use when the rowtypes are related by inheritance, so we expect an exact
 * match of both type and typmod.  The error messages will be a bit unhelpful
 * unless both rowtypes are named composite types.
 */
TupleConversionMap *
convert_tuples_by_name(TupleDesc indesc,
                       TupleDesc outdesc)
{
    TupleConversionMap *map;
    AttrMap    *attrMap;
    int         n = outdesc->natts;

    /* Verify compatibility and prepare attribute-number map */
    attrMap = build_attrmap_by_name_if_req(indesc, outdesc);

    if (attrMap == NULL)
    {
        /* runtime conversion is not needed */
        return NULL;
    }

    /* Prepare the map structure */
    map = (TupleConversionMap *) palloc(sizeof(TupleConversionMap));
    map->indesc = indesc;
    map->outdesc = outdesc;
    map->attrMap = attrMap;
    /* preallocate workspace for Datum arrays */
    map->outvalues = (Datum *) palloc(n * sizeof(Datum));
    map->outisnull = (bool *) palloc(n * sizeof(bool));
    n = indesc->natts + 1;      /* +1 for NULL */
    map->invalues = (Datum *) palloc(n * sizeof(Datum));
    map->inisnull = (bool *) palloc(n * sizeof(bool));
    map->invalues[0] = (Datum) 0;   /* set up the NULL entry */
    map->inisnull[0] = true;

    return map;
}

/*
 * Perform conversion of a tuple according to the map.
 */
HeapTuple
execute_attr_map_tuple(HeapTuple tuple, TupleConversionMap *map)
{
    AttrMap    *attrMap = map->attrMap;
    Datum      *invalues = map->invalues;
    bool       *inisnull = map->inisnull;
    Datum      *outvalues = map->outvalues;
    bool       *outisnull = map->outisnull;
    int         i;

    /*
     * Extract all the values of the old tuple, offsetting the arrays so that
     * invalues[0] is left NULL and invalues[1] is the first source attribute;
     * this exactly matches the numbering convention in attrMap.
     */
    heap_deform_tuple(tuple, map->indesc, invalues + 1, inisnull + 1);

    /*
     * Transpose into proper fields of the new tuple.
     */
    Assert(attrMap->maplen == map->outdesc->natts);
    for (i = 0; i < attrMap->maplen; i++)
    {
        int         j = attrMap->attnums[i];

        outvalues[i] = invalues[j];
        outisnull[i] = inisnull[j];
    }

    /*
     * Now form the new tuple.
     */
    return heap_form_tuple(map->outdesc, outvalues, outisnull);
}

/*
 * Perform conversion of a tuple slot according to the map.
 */
TupleTableSlot *
execute_attr_map_slot(AttrMap *attrMap,
                      TupleTableSlot *in_slot,
                      TupleTableSlot *out_slot)
{
    Datum      *invalues;
    bool       *inisnull;
    Datum      *outvalues;
    bool       *outisnull;
    int         outnatts;
    int         i;

    /* Sanity checks */
    Assert(in_slot->tts_tupleDescriptor != NULL &&
           out_slot->tts_tupleDescriptor != NULL);
    Assert(in_slot->tts_values != NULL && out_slot->tts_values != NULL);

    outnatts = out_slot->tts_tupleDescriptor->natts;

    /* Extract all the values of the in slot. */
    slot_getallattrs(in_slot);

    /* Before doing the mapping, clear any old contents from the out slot */
    ExecClearTuple(out_slot);

    invalues = in_slot->tts_values;
    inisnull = in_slot->tts_isnull;
    outvalues = out_slot->tts_values;
    outisnull = out_slot->tts_isnull;

    /* Transpose into proper fields of the out slot. */
    for (i = 0; i < outnatts; i++)
    {
        int         j = attrMap->attnums[i] - 1;

        /* attrMap->attnums[i] == 0 means it's a NULL datum. */
        if (j == -1)
        {
            outvalues[i] = (Datum) 0;
            outisnull[i] = true;
        }
        else
        {
            outvalues[i] = invalues[j];
            outisnull[i] = inisnull[j];
        }
    }

    ExecStoreVirtualTuple(out_slot);

    return out_slot;
}

/*
 * Free a TupleConversionMap structure.
 */
void
free_conversion_map(TupleConversionMap *map)
{
    /* indesc and outdesc are not ours to free */
    free_attrmap(map->attrMap);
    pfree(map->invalues);
    pfree(map->inisnull);
    pfree(map->outvalues);
    pfree(map->outisnull);
    pfree(map);
}