pg_attrdef.c

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/*-------------------------------------------------------------------------
 *
 * pg_attrdef.c
 *    routines to support manipulation of the pg_attrdef relation
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/catalog/pg_attrdef.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/relation.h"
#include "access/table.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_attrdef.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/rel.h"
#include "utils/syscache.h"
 
 
/*
 * Store a default expression for column attnum of relation rel.
 *
 * Returns the OID of the new pg_attrdef tuple.
 */
Oid
StoreAttrDefault(Relation rel, AttrNumber attnum,
                 Node *expr, bool is_internal)
{
    char       *adbin;
    Relation    adrel;
    HeapTuple   tuple;
    Datum       values[Natts_pg_attrdef];
    static bool nulls[Natts_pg_attrdef] = {false, false, false, false};
    Relation    attrrel;
    HeapTuple   atttup;
    Form_pg_attribute attStruct;
    Datum       valuesAtt[Natts_pg_attribute] = {0};
    bool        nullsAtt[Natts_pg_attribute] = {0};
    bool        replacesAtt[Natts_pg_attribute] = {0};
    char        attgenerated;
    Oid         attrdefOid;
    ObjectAddress colobject,
                defobject;
 
    adrel = table_open(AttrDefaultRelationId, RowExclusiveLock);
 
    /*
     * Flatten expression to string form for storage.
     */
    adbin = nodeToString(expr);
 
    /*
     * Make the pg_attrdef entry.
     */
    attrdefOid = GetNewOidWithIndex(adrel, AttrDefaultOidIndexId,
                                    Anum_pg_attrdef_oid);
    values[Anum_pg_attrdef_oid - 1] = ObjectIdGetDatum(attrdefOid);
    values[Anum_pg_attrdef_adrelid - 1] = ObjectIdGetDatum(RelationGetRelid(rel));
    values[Anum_pg_attrdef_adnum - 1] = Int16GetDatum(attnum);
    values[Anum_pg_attrdef_adbin - 1] = CStringGetTextDatum(adbin);
 
    tuple = heap_form_tuple(adrel->rd_att, values, nulls);
    CatalogTupleInsert(adrel, tuple);
 
    defobject.classId = AttrDefaultRelationId;
    defobject.objectId = attrdefOid;
    defobject.objectSubId = 0;
 
    table_close(adrel, RowExclusiveLock);
 
    /* now can free some of the stuff allocated above */
    pfree(DatumGetPointer(values[Anum_pg_attrdef_adbin - 1]));
    heap_freetuple(tuple);
    pfree(adbin);
 
    /*
     * Update the pg_attribute entry for the column to show that a default
     * exists.
     */
    attrrel = table_open(AttributeRelationId, RowExclusiveLock);
    atttup = SearchSysCacheCopy2(ATTNUM,
                                 ObjectIdGetDatum(RelationGetRelid(rel)),
                                 Int16GetDatum(attnum));
    if (!HeapTupleIsValid(atttup))
        elog(ERROR, "cache lookup failed for attribute %d of relation %u",
             attnum, RelationGetRelid(rel));
    attStruct = (Form_pg_attribute) GETSTRUCT(atttup);
    attgenerated = attStruct->attgenerated;
 
    valuesAtt[Anum_pg_attribute_atthasdef - 1] = BoolGetDatum(true);
    replacesAtt[Anum_pg_attribute_atthasdef - 1] = true;
 
    atttup = heap_modify_tuple(atttup, RelationGetDescr(attrrel),
                               valuesAtt, nullsAtt, replacesAtt);
 
    CatalogTupleUpdate(attrrel, &atttup->t_self, atttup);
 
    table_close(attrrel, RowExclusiveLock);
    heap_freetuple(atttup);
 
    /*
     * Make a dependency so that the pg_attrdef entry goes away if the column
     * (or whole table) is deleted.  In the case of a generated column, make
     * it an internal dependency to prevent the default expression from being
     * deleted separately.
     */
    colobject.classId = RelationRelationId;
    colobject.objectId = RelationGetRelid(rel);
    colobject.objectSubId = attnum;
 
    recordDependencyOn(&defobject, &colobject,
                       attgenerated ? DEPENDENCY_INTERNAL : DEPENDENCY_AUTO);
 
    /*
     * Record dependencies on objects used in the expression, too.
     */
    recordDependencyOnSingleRelExpr(&defobject, expr, RelationGetRelid(rel),
                                    DEPENDENCY_NORMAL,
                                    DEPENDENCY_NORMAL, false);
 
    /*
     * Post creation hook for attribute defaults.
     *
     * XXX. ALTER TABLE ALTER COLUMN SET/DROP DEFAULT is implemented with a
     * couple of deletion/creation of the attribute's default entry, so the
     * callee should check existence of an older version of this entry if it
     * needs to distinguish.
     */
    InvokeObjectPostCreateHookArg(AttrDefaultRelationId,
                                  RelationGetRelid(rel), attnum, is_internal);
 
    return attrdefOid;
}
 
 
/*
 *      RemoveAttrDefault
 *
 * If the specified relation/attribute has a default, remove it.
 * (If no default, raise error if complain is true, else return quietly.)
 */
void
RemoveAttrDefault(Oid relid, AttrNumber attnum,
                  DropBehavior behavior, bool complain, bool internal)
{
    Relation    attrdef_rel;
    ScanKeyData scankeys[2];
    SysScanDesc scan;
    HeapTuple   tuple;
    bool        found = false;
 
    attrdef_rel = table_open(AttrDefaultRelationId, RowExclusiveLock);
 
    ScanKeyInit(&scankeys[0],
                Anum_pg_attrdef_adrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(relid));
    ScanKeyInit(&scankeys[1],
                Anum_pg_attrdef_adnum,
                BTEqualStrategyNumber, F_INT2EQ,
                Int16GetDatum(attnum));
 
    scan = systable_beginscan(attrdef_rel, AttrDefaultIndexId, true,
                              NULL, 2, scankeys);
 
    /* There should be at most one matching tuple, but we loop anyway */
    while (HeapTupleIsValid(tuple = systable_getnext(scan)))
    {
        ObjectAddress object;
        Form_pg_attrdef attrtuple = (Form_pg_attrdef) GETSTRUCT(tuple);
 
        object.classId = AttrDefaultRelationId;
        object.objectId = attrtuple->oid;
        object.objectSubId = 0;
 
        performDeletion(&object, behavior,
                        internal ? PERFORM_DELETION_INTERNAL : 0);
 
        found = true;
    }
 
    systable_endscan(scan);
    table_close(attrdef_rel, RowExclusiveLock);
 
    if (complain && !found)
        elog(ERROR, "could not find attrdef tuple for relation %u attnum %d",
             relid, attnum);
}
 
/*
 *      RemoveAttrDefaultById
 *
 * Remove a pg_attrdef entry specified by OID.  This is the guts of
 * attribute-default removal.  Note it should be called via performDeletion,
 * not directly.
 */
void
RemoveAttrDefaultById(Oid attrdefId)
{
    Relation    attrdef_rel;
    Relation    attr_rel;
    Relation    myrel;
    ScanKeyData scankeys[1];
    SysScanDesc scan;
    HeapTuple   tuple;
    Oid         myrelid;
    AttrNumber  myattnum;
 
    /* Grab an appropriate lock on the pg_attrdef relation */
    attrdef_rel = table_open(AttrDefaultRelationId, RowExclusiveLock);
 
    /* Find the pg_attrdef tuple */
    ScanKeyInit(&scankeys[0],
                Anum_pg_attrdef_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(attrdefId));
 
    scan = systable_beginscan(attrdef_rel, AttrDefaultOidIndexId, true,
                              NULL, 1, scankeys);
 
    tuple = systable_getnext(scan);
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "could not find tuple for attrdef %u", attrdefId);
 
    myrelid = ((Form_pg_attrdef) GETSTRUCT(tuple))->adrelid;
    myattnum = ((Form_pg_attrdef) GETSTRUCT(tuple))->adnum;
 
    /* Get an exclusive lock on the relation owning the attribute */
    myrel = relation_open(myrelid, AccessExclusiveLock);
 
    /* Now we can delete the pg_attrdef row */
    CatalogTupleDelete(attrdef_rel, &tuple->t_self);
 
    systable_endscan(scan);
    table_close(attrdef_rel, RowExclusiveLock);
 
    /* Fix the pg_attribute row */
    attr_rel = table_open(AttributeRelationId, RowExclusiveLock);
 
    tuple = SearchSysCacheCopy2(ATTNUM,
                                ObjectIdGetDatum(myrelid),
                                Int16GetDatum(myattnum));
    if (!HeapTupleIsValid(tuple))   /* shouldn't happen */
        elog(ERROR, "cache lookup failed for attribute %d of relation %u",
             myattnum, myrelid);
 
    ((Form_pg_attribute) GETSTRUCT(tuple))->atthasdef = false;
 
    CatalogTupleUpdate(attr_rel, &tuple->t_self, tuple);
 
    /*
     * Our update of the pg_attribute row will force a relcache rebuild, so
     * there's nothing else to do here.
     */
    table_close(attr_rel, RowExclusiveLock);
 
    /* Keep lock on attribute's rel until end of xact */
    relation_close(myrel, NoLock);
}
 
 
/*
 * Get the pg_attrdef OID of the default expression for a column
 * identified by relation OID and column number.
 *
 * Returns InvalidOid if there is no such pg_attrdef entry.
 */
Oid
GetAttrDefaultOid(Oid relid, AttrNumber attnum)
{
    Oid         result = InvalidOid;
    Relation    attrdef;
    ScanKeyData keys[2];
    SysScanDesc scan;
    HeapTuple   tup;
 
    attrdef = table_open(AttrDefaultRelationId, AccessShareLock);
    ScanKeyInit(&keys[0],
                Anum_pg_attrdef_adrelid,
                BTEqualStrategyNumber,
                F_OIDEQ,
                ObjectIdGetDatum(relid));
    ScanKeyInit(&keys[1],
                Anum_pg_attrdef_adnum,
                BTEqualStrategyNumber,
                F_INT2EQ,
                Int16GetDatum(attnum));
    scan = systable_beginscan(attrdef, AttrDefaultIndexId, true,
                              NULL, 2, keys);
 
    if (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_attrdef atdform = (Form_pg_attrdef) GETSTRUCT(tup);
 
        result = atdform->oid;
    }
 
    systable_endscan(scan);
    table_close(attrdef, AccessShareLock);
 
    return result;
}
 
/*
 * Given a pg_attrdef OID, return the relation OID and column number of
 * the owning column (represented as an ObjectAddress for convenience).
 *
 * Returns InvalidObjectAddress if there is no such pg_attrdef entry.
 */
ObjectAddress
GetAttrDefaultColumnAddress(Oid attrdefoid)
{
    ObjectAddress result = InvalidObjectAddress;
    Relation    attrdef;
    ScanKeyData skey[1];
    SysScanDesc scan;
    HeapTuple   tup;
 
    attrdef = table_open(AttrDefaultRelationId, AccessShareLock);
    ScanKeyInit(&skey[0],
                Anum_pg_attrdef_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(attrdefoid));
    scan = systable_beginscan(attrdef, AttrDefaultOidIndexId, true,
                              NULL, 1, skey);
 
    if (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_attrdef atdform = (Form_pg_attrdef) GETSTRUCT(tup);
 
        result.classId = RelationRelationId;
        result.objectId = atdform->adrelid;
        result.objectSubId = atdform->adnum;
    }
 
    systable_endscan(scan);
    table_close(attrdef, AccessShareLock);
 
    return result;
}