postgres/src/backend/access/common/tupconvert.c

/*-------------------------------------------------------------------------
 *
 * 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);
}