PostgreSQL/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.  There is some overlap of functionality with the
 * executor's "junkfilter" routines, but these functions work on bare
 * HeapTuples rather than TupleTableSlots.
 *
 * Portions Copyright (c) 1996-2018, 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/htup_details.h"
#include "access/tupconvert.h"
#include "utils/builtins.h"


/*
 * The conversion setup routines have the following common API:
 *
 * The setup routine checks 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 do_convert_tuple
 * 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.)
 *
 * Note: the errdetail messages speak of indesc as the "returned" rowtype,
 * outdesc as the "expected" rowtype.  This is okay for current uses but
 * might need generalization in future.
 */
TupleConversionMap *
convert_tuples_by_position(TupleDesc indesc,
						   TupleDesc outdesc,
						   const char *msg)
{
	TupleConversionMap *map;
	AttrNumber *attrMap;
	int			nincols;
	int			noutcols;
	int			n;
	int			i;
	int			j;
	bool		same;

	/* Verify compatibility and prepare attribute-number map */
	n = outdesc->natts;
	attrMap = (AttrNumber *) palloc0(n * sizeof(AttrNumber));
	j = 0;						/* j is next physical input attribute */
	nincols = noutcols = 0;		/* these count non-dropped attributes */
	same = true;
	for (i = 0; i < n; i++)
	{
		Form_pg_attribute att = TupleDescAttr(outdesc, i);
		Oid			atttypid;
		int32		atttypmod;

		if (att->attisdropped)
			continue;			/* attrMap[i] is already 0 */
		noutcols++;
		atttypid = att->atttypid;
		atttypmod = att->atttypmod;
		for (; j < indesc->natts; j++)
		{
			att = TupleDescAttr(indesc, j);
			if (att->attisdropped)
				continue;
			nincols++;
			/* Found matching column, check type */
			if (atttypid != att->atttypid ||
				(atttypmod != att->atttypmod && atttypmod >= 0))
				ereport(ERROR,
						(errcode(ERRCODE_DATATYPE_MISMATCH),
						 errmsg_internal("%s", _(msg)),
						 errdetail("Returned type %s does not match expected type %s in column %d.",
								   format_type_with_typemod(att->atttypid,
															att->atttypmod),
								   format_type_with_typemod(atttypid,
															atttypmod),
								   noutcols)));
			attrMap[i] = (AttrNumber) (j + 1);
			j++;
			break;
		}
		if (attrMap[i] == 0)
			same = false;		/* we'll complain below */
	}

	/* Check for unused input columns */
	for (; j < indesc->natts; j++)
	{
		if (TupleDescAttr(indesc, j)->attisdropped)
			continue;
		nincols++;
		same = false;			/* we'll complain below */
	}

	/* Report column count mismatch using the non-dropped-column counts */
	if (!same)
		ereport(ERROR,
				(errcode(ERRCODE_DATATYPE_MISMATCH),
				 errmsg_internal("%s", _(msg)),
				 errdetail("Number of returned columns (%d) does not match "
						   "expected column count (%d).",
						   nincols, noutcols)));

	/*
	 * Check to see if the map is one-to-one, in which case we need not do a
	 * tuple conversion.  We must also insist that both tupdescs either
	 * specify or don't specify an OID column, else we need a conversion to
	 * add/remove space for that.  (For some callers, presence or absence of
	 * an OID column perhaps would not really matter, but let's be safe.)
	 */
	if (indesc->natts == outdesc->natts &&
		indesc->tdhasoid == outdesc->tdhasoid)
	{
		for (i = 0; i < n; i++)
		{
			Form_pg_attribute inatt;
			Form_pg_attribute outatt;

			if (attrMap[i] == (i + 1))
				continue;

			/*
			 * If it's a dropped column and the corresponding input column is
			 * also dropped, we needn't convert.  However, attlen and attalign
			 * must agree.
			 */
			inatt = TupleDescAttr(indesc, i);
			outatt = TupleDescAttr(outdesc, i);
			if (attrMap[i] == 0 &&
				inatt->attisdropped &&
				inatt->attlen == outatt->attlen &&
				inatt->attalign == outatt->attalign)
				continue;

			same = false;
			break;
		}
	}
	else
		same = false;

	if (same)
	{
		/* Runtime conversion is not needed */
		pfree(attrMap);
		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;
}

/*
 * 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,
					   const char *msg)
{
	TupleConversionMap *map;
	AttrNumber *attrMap;
	int			n = outdesc->natts;
	int			i;
	bool		same;

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

	/*
	 * Check to see if the map is one-to-one, in which case we need not do a
	 * tuple conversion.  We must also insist that both tupdescs either
	 * specify or don't specify an OID column, else we need a conversion to
	 * add/remove space for that.  (For some callers, presence or absence of
	 * an OID column perhaps would not really matter, but let's be safe.)
	 */
	if (indesc->natts == outdesc->natts &&
		indesc->tdhasoid == outdesc->tdhasoid)
	{
		same = true;
		for (i = 0; i < n; i++)
		{
			Form_pg_attribute inatt;
			Form_pg_attribute outatt;

			if (attrMap[i] == (i + 1))
				continue;

			/*
			 * If it's a dropped column and the corresponding input column is
			 * also dropped, we needn't convert.  However, attlen and attalign
			 * must agree.
			 */
			inatt = TupleDescAttr(indesc, i);
			outatt = TupleDescAttr(outdesc, i);
			if (attrMap[i] == 0 &&
				inatt->attisdropped &&
				inatt->attlen == outatt->attlen &&
				inatt->attalign == outatt->attalign)
				continue;

			same = false;
			break;
		}
	}
	else
		same = false;

	if (same)
	{
		/* Runtime conversion is not needed */
		pfree(attrMap);
		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;
}

/*
 * Return a palloc'd bare attribute map for tuple conversion, matching input
 * and output columns by name.  (Dropped columns are ignored in both input and
 * output.)  This is normally a subroutine for convert_tuples_by_name, but can
 * be used standalone.
 */
AttrNumber *
convert_tuples_by_name_map(TupleDesc indesc,
						   TupleDesc outdesc,
						   const char *msg)
{
	AttrNumber *attrMap;
	int			outnatts;
	int			innatts;
	int			i;
	int			nextindesc = -1;

	outnatts = outdesc->natts;
	innatts = indesc->natts;

	attrMap = (AttrNumber *) palloc0(outnatts * sizeof(AttrNumber));
	for (i = 0; i < outnatts; i++)
	{
		Form_pg_attribute outatt = TupleDescAttr(outdesc, i);
		char	   *attname;
		Oid			atttypid;
		int32		atttypmod;
		int			j;

		if (outatt->attisdropped)
			continue;			/* attrMap[i] is already 0 */
		attname = NameStr(outatt->attname);
		atttypid = outatt->atttypid;
		atttypmod = outatt->atttypmod;

		/*
		 * Now search for an attribute with the same name in the indesc. It
		 * seems likely that a partitioned table will have the attributes in
		 * the same order as the partition, so the search below is optimized
		 * for that case.  It is possible that columns are dropped in one of
		 * the relations, but not the other, so we use the 'nextindesc'
		 * counter to track the starting point of the search.  If the inner
		 * loop encounters dropped columns then it will have to skip over
		 * them, but it should leave 'nextindesc' at the correct position for
		 * the next outer loop.
		 */
		for (j = 0; j < innatts; j++)
		{
			Form_pg_attribute inatt;

			nextindesc++;
			if (nextindesc >= innatts)
				nextindesc = 0;

			inatt = TupleDescAttr(indesc, nextindesc);
			if (inatt->attisdropped)
				continue;
			if (strcmp(attname, NameStr(inatt->attname)) == 0)
			{
				/* Found it, check type */
				if (atttypid != inatt->atttypid || atttypmod != inatt->atttypmod)
					ereport(ERROR,
							(errcode(ERRCODE_DATATYPE_MISMATCH),
							 errmsg_internal("%s", _(msg)),
							 errdetail("Attribute \"%s\" of type %s does not match corresponding attribute of type %s.",
									   attname,
									   format_type_be(outdesc->tdtypeid),
									   format_type_be(indesc->tdtypeid))));
				attrMap[i] = inatt->attnum;
				break;
			}
		}
		if (attrMap[i] == 0)
			ereport(ERROR,
					(errcode(ERRCODE_DATATYPE_MISMATCH),
					 errmsg_internal("%s", _(msg)),
					 errdetail("Attribute \"%s\" of type %s does not exist in type %s.",
							   attname,
							   format_type_be(outdesc->tdtypeid),
							   format_type_be(indesc->tdtypeid))));
	}
	return attrMap;
}

/*
 * Perform conversion of a tuple according to the map.
 */
HeapTuple
do_convert_tuple(HeapTuple tuple, TupleConversionMap *map)
{
	AttrNumber *attrMap = map->attrMap;
	Datum	   *invalues = map->invalues;
	bool	   *inisnull = map->inisnull;
	Datum	   *outvalues = map->outvalues;
	bool	   *outisnull = map->outisnull;
	int			outnatts = map->outdesc->natts;
	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.
	 */
	for (i = 0; i < outnatts; i++)
	{
		int			j = attrMap[i];

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

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

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