src/include/access/tupdesc.h

/*-------------------------------------------------------------------------
 *
 * tupdesc.h
 *	  POSTGRES tuple descriptor definitions.
 *
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/access/tupdesc.h,v 1.51 2006/10/04 00:30:07 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef TUPDESC_H
#define TUPDESC_H

#include "access/attnum.h"
#include "catalog/pg_attribute.h"
#include "nodes/pg_list.h"


typedef struct attrDefault
{
	AttrNumber	adnum;
	char	   *adbin;			/* nodeToString representation of expr */
} AttrDefault;

typedef struct constrCheck
{
	char	   *ccname;
	char	   *ccbin;			/* nodeToString representation of expr */
} ConstrCheck;

/* This structure contains constraints of a tuple */
typedef struct tupleConstr
{
	AttrDefault *defval;		/* array */
	ConstrCheck *check;			/* array */
	uint16		num_defval;
	uint16		num_check;
	bool		has_not_null;
} TupleConstr;

/*
 * This struct is passed around within the backend to describe the structure
 * of tuples.  For tuples coming from on-disk relations, the information is
 * collected from the pg_attribute, pg_attrdef, and pg_constraint catalogs.
 * Transient row types (such as the result of a join query) have anonymous
 * TupleDesc structs that generally omit any constraint info; therefore the
 * structure is designed to let the constraints be omitted efficiently.
 *
 * Note that only user attributes, not system attributes, are mentioned in
 * TupleDesc; with the exception that tdhasoid indicates if OID is present.
 *
 * If the tupdesc is known to correspond to a named rowtype (such as a table's
 * rowtype) then tdtypeid identifies that type and tdtypmod is -1.	Otherwise
 * tdtypeid is RECORDOID, and tdtypmod can be either -1 for a fully anonymous
 * row type, or a value >= 0 to allow the rowtype to be looked up in the
 * typcache.c type cache.
 *
 * Tuple descriptors that live in caches (relcache or typcache, at present)
 * are reference-counted: they can be deleted when their reference count goes
 * to zero.  Tuple descriptors created by the executor need no reference
 * counting, however: they are simply created in the appropriate memory
 * context and go away when the context is freed.  We set the tdrefcount
 * field of such a descriptor to -1, while reference-counted descriptors
 * always have tdrefcount >= 0.
 */
typedef struct tupleDesc
{
	int			natts;			/* number of attributes in the tuple */
	Form_pg_attribute *attrs;
	/* attrs[N] is a pointer to the description of Attribute Number N+1 */
	TupleConstr *constr;		/* constraints, or NULL if none */
	Oid			tdtypeid;		/* composite type ID for tuple type */
	int32		tdtypmod;		/* typmod for tuple type */
	bool		tdhasoid;		/* tuple has oid attribute in its header */
	int			tdrefcount;		/* reference count, or -1 if not counting */
}	*TupleDesc;


extern TupleDesc CreateTemplateTupleDesc(int natts, bool hasoid);

extern TupleDesc CreateTupleDesc(int natts, bool hasoid,
				Form_pg_attribute *attrs);

extern TupleDesc CreateTupleDescCopy(TupleDesc tupdesc);

extern TupleDesc CreateTupleDescCopyConstr(TupleDesc tupdesc);

extern void FreeTupleDesc(TupleDesc tupdesc);

extern void IncrTupleDescRefCount(TupleDesc tupdesc);
extern void DecrTupleDescRefCount(TupleDesc tupdesc);

#define PinTupleDesc(tupdesc) \
	do { \
		if ((tupdesc)->tdrefcount >= 0) \
			IncrTupleDescRefCount(tupdesc); \
	} while (0)

#define ReleaseTupleDesc(tupdesc) \
	do { \
		if ((tupdesc)->tdrefcount > 0) \
			DecrTupleDescRefCount(tupdesc); \
	} while (0)

extern bool equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2, bool strict);

extern void TupleDescInitEntry(TupleDesc desc,
				   AttrNumber attributeNumber,
				   const char *attributeName,
				   Oid oidtypeid,
				   int32 typmod,
				   int attdim);

extern TupleDesc BuildDescForRelation(List *schema);

extern TupleDesc BuildDescFromLists(List *names, List *types, List *typmods);

#endif   /* TUPDESC_H */