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postgresql/src/backend/commands/comment.c

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/*-------------------------------------------------------------------------
*
* comment.c
*
* PostgreSQL object comments utility code.
*
* Copyright (c) 1996-2001, PostgreSQL Global Development Group
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/commands/comment.c,v 1.56 2002/08/09 16:45:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/genam.h"
#include "access/heapam.h"
#include "catalog/catname.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_description.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_rewrite.h"
#include "catalog/pg_trigger.h"
#include "commands/comment.h"
#include "commands/dbcommands.h"
#include "miscadmin.h"
#include "parser/parse_func.h"
#include "parser/parse_oper.h"
#include "parser/parse_type.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
/*
* Static Function Prototypes --
*
* The following protoypes are declared static so as not to conflict
* with any other routines outside this module. These routines are
* called by the public function CommentObject() routine to create
* the appropriate comment for the specific object type.
*/
static void CommentRelation(int objtype, List *relname, char *comment);
static void CommentAttribute(List *qualname, char *comment);
static void CommentDatabase(List *qualname, char *comment);
static void CommentNamespace(List *qualname, char *comment);
static void CommentRule(List *qualname, char *comment);
static void CommentType(List *typename, char *comment);
static void CommentAggregate(List *aggregate, List *arguments, char *comment);
static void CommentProc(List *function, List *arguments, char *comment);
static void CommentOperator(List *opername, List *arguments, char *comment);
static void CommentTrigger(List *qualname, char *comment);
static void CommentConstraint(List *qualname, char *comment);
/*
* CommentObject --
*
* This routine is used to add the associated comment into
* pg_description for the object specified by the given SQL command.
*/
void
CommentObject(CommentStmt *stmt)
{
switch (stmt->objtype)
{
case COMMENT_ON_INDEX:
case COMMENT_ON_SEQUENCE:
case COMMENT_ON_TABLE:
case COMMENT_ON_VIEW:
CommentRelation(stmt->objtype, stmt->objname, stmt->comment);
break;
case COMMENT_ON_COLUMN:
CommentAttribute(stmt->objname, stmt->comment);
break;
case COMMENT_ON_DATABASE:
CommentDatabase(stmt->objname, stmt->comment);
break;
case COMMENT_ON_RULE:
CommentRule(stmt->objname, stmt->comment);
break;
case COMMENT_ON_TYPE:
CommentType(stmt->objname, stmt->comment);
break;
case COMMENT_ON_AGGREGATE:
CommentAggregate(stmt->objname, stmt->objargs, stmt->comment);
break;
case COMMENT_ON_FUNCTION:
CommentProc(stmt->objname, stmt->objargs, stmt->comment);
break;
case COMMENT_ON_OPERATOR:
CommentOperator(stmt->objname, stmt->objargs, stmt->comment);
break;
case COMMENT_ON_TRIGGER:
CommentTrigger(stmt->objname, stmt->comment);
break;
case COMMENT_ON_SCHEMA:
CommentNamespace(stmt->objname, stmt->comment);
break;
case COMMENT_ON_CONSTRAINT:
CommentConstraint(stmt->objname, stmt->comment);
break;
default:
elog(ERROR, "An attempt was made to comment on a unknown type: %d",
stmt->objtype);
}
}
/*
* CreateComments --
*
* Create a comment for the specified object descriptor. Inserts a new
* pg_description tuple, or replaces an existing one with the same key.
*
* If the comment given is null or an empty string, instead delete any
* existing comment for the specified key.
*/
void
CreateComments(Oid oid, Oid classoid, int32 subid, char *comment)
{
Relation description;
ScanKeyData skey[3];
SysScanDesc sd;
HeapTuple oldtuple;
HeapTuple newtuple = NULL;
Datum values[Natts_pg_description];
char nulls[Natts_pg_description];
char replaces[Natts_pg_description];
int i;
/* Reduce empty-string to NULL case */
if (comment != NULL && strlen(comment) == 0)
comment = NULL;
/* Prepare to form or update a tuple, if necessary */
if (comment != NULL)
{
for (i = 0; i < Natts_pg_description; i++)
{
nulls[i] = ' ';
replaces[i] = 'r';
}
i = 0;
values[i++] = ObjectIdGetDatum(oid);
values[i++] = ObjectIdGetDatum(classoid);
values[i++] = Int32GetDatum(subid);
values[i++] = DirectFunctionCall1(textin, CStringGetDatum(comment));
}
/* Use the index to search for a matching old tuple */
ScanKeyEntryInitialize(&skey[0],
(bits16) 0x0,
(AttrNumber) 1,
(RegProcedure) F_OIDEQ,
ObjectIdGetDatum(oid));
ScanKeyEntryInitialize(&skey[1],
(bits16) 0x0,
(AttrNumber) 2,
(RegProcedure) F_OIDEQ,
ObjectIdGetDatum(classoid));
ScanKeyEntryInitialize(&skey[2],
(bits16) 0x0,
(AttrNumber) 3,
(RegProcedure) F_INT4EQ,
Int32GetDatum(subid));
description = heap_openr(DescriptionRelationName, RowExclusiveLock);
sd = systable_beginscan(description, DescriptionObjIndex, true,
SnapshotNow, 3, skey);
while ((oldtuple = systable_getnext(sd)) != NULL)
{
/* Found the old tuple, so delete or update it */
if (comment == NULL)
simple_heap_delete(description, &oldtuple->t_self);
else
{
newtuple = heap_modifytuple(oldtuple, description, values,
nulls, replaces);
simple_heap_update(description, &oldtuple->t_self, newtuple);
}
break; /* Assume there can be only one match */
}
systable_endscan(sd);
/* If we didn't find an old tuple, insert a new one */
if (newtuple == NULL && comment != NULL)
{
newtuple = heap_formtuple(RelationGetDescr(description),
values, nulls);
simple_heap_insert(description, newtuple);
}
/* Update indexes, if necessary */
if (newtuple != NULL)
{
CatalogUpdateIndexes(description, newtuple);
heap_freetuple(newtuple);
}
/* Done */
heap_close(description, NoLock);
}
/*
* DeleteComments -- remove comments for an object
*
* If subid is nonzero then only comments matching it will be removed.
* If subid is zero, all comments matching the oid/classoid will be removed
* (this corresponds to deleting a whole object).
*/
void
DeleteComments(Oid oid, Oid classoid, int32 subid)
{
Relation description;
ScanKeyData skey[3];
int nkeys;
SysScanDesc sd;
HeapTuple oldtuple;
/* Use the index to search for all matching old tuples */
ScanKeyEntryInitialize(&skey[0], 0x0,
Anum_pg_description_objoid, F_OIDEQ,
ObjectIdGetDatum(oid));
ScanKeyEntryInitialize(&skey[1], 0x0,
Anum_pg_description_classoid, F_OIDEQ,
ObjectIdGetDatum(classoid));
if (subid != 0)
{
ScanKeyEntryInitialize(&skey[2], 0x0,
Anum_pg_description_objsubid, F_INT4EQ,
Int32GetDatum(subid));
nkeys = 3;
}
else
nkeys = 2;
description = heap_openr(DescriptionRelationName, RowExclusiveLock);
sd = systable_beginscan(description, DescriptionObjIndex, true,
SnapshotNow, nkeys, skey);
while ((oldtuple = systable_getnext(sd)) != NULL)
{
simple_heap_delete(description, &oldtuple->t_self);
}
/* Done */
systable_endscan(sd);
heap_close(description, RowExclusiveLock);
}
/*
* CommentRelation --
*
* This routine is used to add/drop a comment from a relation, where
* a relation is a TABLE, SEQUENCE, VIEW or INDEX. The routine simply
* finds the relation name by searching the system cache, locating
* the appropriate tuple, and inserting a comment using that
* tuple's oid. Its parameters are the relation name and comments.
*/
static void
CommentRelation(int objtype, List *relname, char *comment)
{
Relation relation;
RangeVar *tgtrel;
tgtrel = makeRangeVarFromNameList(relname);
/*
* Open the relation. We do this mainly to acquire a lock that
* ensures no one else drops the relation before we commit. (If they
* did, they'd fail to remove the entry we are about to make in
* pg_description.)
*/
relation = relation_openrv(tgtrel, AccessShareLock);
/* Check object security */
if (!pg_class_ownercheck(RelationGetRelid(relation), GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(relation));
/* Next, verify that the relation type matches the intent */
switch (objtype)
{
case COMMENT_ON_INDEX:
if (relation->rd_rel->relkind != RELKIND_INDEX)
elog(ERROR, "relation \"%s\" is not an index",
RelationGetRelationName(relation));
break;
case COMMENT_ON_SEQUENCE:
if (relation->rd_rel->relkind != RELKIND_SEQUENCE)
elog(ERROR, "relation \"%s\" is not a sequence",
RelationGetRelationName(relation));
break;
case COMMENT_ON_TABLE:
if (relation->rd_rel->relkind != RELKIND_RELATION)
elog(ERROR, "relation \"%s\" is not a table",
RelationGetRelationName(relation));
break;
case COMMENT_ON_VIEW:
if (relation->rd_rel->relkind != RELKIND_VIEW)
elog(ERROR, "relation \"%s\" is not a view",
RelationGetRelationName(relation));
break;
}
/* Create the comment using the relation's oid */
CreateComments(RelationGetRelid(relation), RelOid_pg_class, 0, comment);
/* Done, but hold lock until commit */
relation_close(relation, NoLock);
}
/*
* CommentAttribute --
*
* This routine is used to add/drop a comment from an attribute
* such as a table's column. The routine will check security
* restrictions and then attempt to look up the specified
* attribute. If successful, a comment is added/dropped, else an
* elog() exception is thrown. The parameters are the relation
* and attribute names, and the comments
*/
static void
CommentAttribute(List *qualname, char *comment)
{
int nnames;
List *relname;
char *attrname;
RangeVar *rel;
Relation relation;
AttrNumber attnum;
/* Separate relname and attr name */
nnames = length(qualname);
if (nnames < 2)
elog(ERROR, "CommentAttribute: must specify relation.attribute");
relname = ltruncate(nnames-1, listCopy(qualname));
attrname = strVal(nth(nnames-1, qualname));
/* Open the containing relation to ensure it won't go away meanwhile */
rel = makeRangeVarFromNameList(relname);
relation = heap_openrv(rel, AccessShareLock);
/* Check object security */
if (!pg_class_ownercheck(RelationGetRelid(relation), GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(relation));
/* Now, fetch the attribute number from the system cache */
attnum = get_attnum(RelationGetRelid(relation), attrname);
if (attnum == InvalidAttrNumber)
elog(ERROR, "Relation \"%s\" has no column \"%s\"",
RelationGetRelationName(relation), attrname);
/* Create the comment using the relation's oid */
CreateComments(RelationGetRelid(relation), RelOid_pg_class,
(int32) attnum, comment);
/* Done, but hold lock until commit */
heap_close(relation, NoLock);
}
/*
* CommentDatabase --
*
* This routine is used to add/drop any user-comments a user might
* have regarding the specified database. The routine will check
* security for owner permissions, and, if succesful, will then
* attempt to find the oid of the database specified. Once found,
* a comment is added/dropped using the CreateComments() routine.
*/
static void
CommentDatabase(List *qualname, char *comment)
{
char *database;
Oid oid;
if (length(qualname) != 1)
elog(ERROR, "CommentDatabase: database name may not be qualified");
database = strVal(lfirst(qualname));
/* First get the database OID */
oid = get_database_oid(database);
if (!OidIsValid(oid))
elog(ERROR, "database \"%s\" does not exist", database);
/* Allow if the user matches the database dba or is a superuser */
if (!(superuser() || is_dbadmin(oid)))
elog(ERROR, "you are not permitted to comment on database \"%s\"",
database);
/* Only allow comments on the current database */
if (oid != MyDatabaseId)
elog(ERROR, "Database comments may only be applied to the current database");
/* Create the comment with the pg_database oid */
CreateComments(oid, RelOid_pg_database, 0, comment);
}
/*
* CommentNamespace --
*
* This routine is used to add/drop any user-comments a user might
* have regarding the specified namespace. The routine will check
* security for owner permissions, and, if succesful, will then
* attempt to find the oid of the namespace specified. Once found,
* a comment is added/dropped using the CreateComments() routine.
*/
static void
CommentNamespace(List *qualname, char *comment)
{
Oid oid;
Oid classoid;
char *namespace;
if (length(qualname) != 1)
elog(ERROR, "CommentSchema: schema name may not be qualified");
namespace = strVal(lfirst(qualname));
oid = GetSysCacheOid(NAMESPACENAME,
CStringGetDatum(namespace),
0, 0, 0);
if (!OidIsValid(oid))
elog(ERROR, "CommentSchema: Schema \"%s\" could not be found",
namespace);
/* Check object security */
if (!pg_namespace_ownercheck(oid, GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, namespace);
/* pg_namespace doesn't have a hard-coded OID, so must look it up */
classoid = get_system_catalog_relid(NamespaceRelationName);
/* Call CreateComments() to create/drop the comments */
CreateComments(oid, classoid, 0, comment);
}
/*
* CommentRule --
*
* This routine is used to add/drop any user-comments a user might
* have regarding a specified RULE. The rule for commenting is determined by
* both its name and the relation to which it refers. The arguments to this
* function are the rule name and relation name (merged into a qualified
* name), and the comment to add/drop.
*
* Before PG 7.3, rules had unique names across the whole database, and so
* the syntax was just COMMENT ON RULE rulename, with no relation name.
* For purposes of backwards compatibility, we support that as long as there
* is only one rule by the specified name in the database.
*/
static void
CommentRule(List *qualname, char *comment)
{
int nnames;
List *relname;
char *rulename;
RangeVar *rel;
Relation relation;
HeapTuple tuple;
Oid reloid;
Oid ruleoid;
Oid classoid;
AclResult aclcheck;
/* Separate relname and trig name */
nnames = length(qualname);
if (nnames == 1)
{
/* Old-style: only a rule name is given */
Relation RewriteRelation;
HeapScanDesc scanDesc;
ScanKeyData scanKeyData;
rulename = strVal(lfirst(qualname));
/* Search pg_rewrite for such a rule */
ScanKeyEntryInitialize(&scanKeyData,
0,
Anum_pg_rewrite_rulename,
F_NAMEEQ,
PointerGetDatum(rulename));
RewriteRelation = heap_openr(RewriteRelationName, AccessShareLock);
scanDesc = heap_beginscan(RewriteRelation, SnapshotNow,
1, &scanKeyData);
tuple = heap_getnext(scanDesc, ForwardScanDirection);
if (HeapTupleIsValid(tuple))
{
reloid = ((Form_pg_rewrite) GETSTRUCT(tuple))->ev_class;
AssertTupleDescHasOid(RewriteRelation->rd_att);
ruleoid = HeapTupleGetOid(tuple);
}
else
{
elog(ERROR, "rule \"%s\" does not exist", rulename);
reloid = ruleoid = 0; /* keep compiler quiet */
}
if (HeapTupleIsValid(tuple = heap_getnext(scanDesc,
ForwardScanDirection)))
elog(ERROR, "There are multiple rules \"%s\""
"\n\tPlease specify a relation name as well as a rule name",
rulename);
heap_endscan(scanDesc);
heap_close(RewriteRelation, AccessShareLock);
/* Open the owning relation to ensure it won't go away meanwhile */
relation = heap_open(reloid, AccessShareLock);
}
else
{
/* New-style: rule and relname both provided */
Assert(nnames >= 2);
relname = ltruncate(nnames-1, listCopy(qualname));
rulename = strVal(nth(nnames-1, qualname));
/* Open the owning relation to ensure it won't go away meanwhile */
rel = makeRangeVarFromNameList(relname);
relation = heap_openrv(rel, AccessShareLock);
reloid = RelationGetRelid(relation);
/* Find the rule's pg_rewrite tuple, get its OID */
tuple = SearchSysCache(RULERELNAME,
ObjectIdGetDatum(reloid),
PointerGetDatum(rulename),
0, 0);
if (!HeapTupleIsValid(tuple))
elog(ERROR, "rule \"%s\" does not exist", rulename);
Assert(reloid == ((Form_pg_rewrite) GETSTRUCT(tuple))->ev_class);
AssertTupleDescHasOid(relation->rd_att);
ruleoid = HeapTupleGetOid(tuple);
ReleaseSysCache(tuple);
}
/* Check object security */
aclcheck = pg_class_aclcheck(reloid, GetUserId(), ACL_RULE);
if (aclcheck != ACLCHECK_OK)
aclcheck_error(aclcheck, rulename);
/* pg_rewrite doesn't have a hard-coded OID, so must look it up */
classoid = get_system_catalog_relid(RewriteRelationName);
/* Call CreateComments() to create/drop the comments */
CreateComments(ruleoid, classoid, 0, comment);
}
/*
* CommentType --
*
* This routine is used to add/drop any user-comments a user might
* have regarding a TYPE. The type is specified by name
* and, if found, and the user has appropriate permissions, a
* comment will be added/dropped using the CreateComments() routine.
* The type's name and the comments are the paramters to this routine.
*/
static void
CommentType(List *typename, char *comment)
{
TypeName *tname;
Oid oid;
/* XXX a bit of a crock; should accept TypeName in COMMENT syntax */
tname = makeNode(TypeName);
tname->names = typename;
tname->typmod = -1;
/* Find the type's oid */
oid = typenameTypeId(tname);
/* Check object security */
if (!pg_type_ownercheck(oid, GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, TypeNameToString(tname));
/* Call CreateComments() to create/drop the comments */
CreateComments(oid, RelOid_pg_type, 0, comment);
}
/*
* CommentAggregate --
*
* This routine is used to allow a user to provide comments on an
* aggregate function. The aggregate function is determined by both
* its name and its argument type, which, with the comments are
* the three parameters handed to this routine.
*/
static void
CommentAggregate(List *aggregate, List *arguments, char *comment)
{
TypeName *aggtype = (TypeName *) lfirst(arguments);
Oid baseoid,
oid;
/* First, attempt to determine the base aggregate oid */
if (aggtype)
baseoid = typenameTypeId(aggtype);
else
baseoid = InvalidOid;
/* Now, attempt to find the actual tuple in pg_proc */
oid = find_aggregate_func("CommentAggregate", aggregate, baseoid);
/* Next, validate the user's attempt to comment */
if (!pg_proc_ownercheck(oid, GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, NameListToString(aggregate));
/* Call CreateComments() to create/drop the comments */
CreateComments(oid, RelOid_pg_proc, 0, comment);
}
/*
* CommentProc --
*
* This routine is used to allow a user to provide comments on an
* procedure (function). The procedure is determined by both
* its name and its argument list. The argument list is expected to
* be a series of parsed nodes pointed to by a List object. If the
* comments string is empty, the associated comment is dropped.
*/
static void
CommentProc(List *function, List *arguments, char *comment)
{
Oid oid;
/* Look up the procedure */
oid = LookupFuncNameTypeNames(function, arguments,
true, "CommentProc");
/* Now, validate the user's ability to comment on this function */
if (!pg_proc_ownercheck(oid, GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, NameListToString(function));
/* Call CreateComments() to create/drop the comments */
CreateComments(oid, RelOid_pg_proc, 0, comment);
}
/*
* CommentOperator --
*
* This routine is used to allow a user to provide comments on an
* operator. The operator for commenting is determined by both
* its name and its argument list which defines the left and right
* hand types the operator will operate on. The argument list is
* expected to be a couple of parse nodes pointed to be a List
* object.
*/
static void
CommentOperator(List *opername, List *arguments, char *comment)
{
TypeName *typenode1 = (TypeName *) lfirst(arguments);
TypeName *typenode2 = (TypeName *) lsecond(arguments);
Oid oid;
Oid classoid;
/* Look up the operator */
oid = LookupOperNameTypeNames(opername, typenode1, typenode2,
"CommentOperator");
/* Valid user's ability to comment on this operator */
if (!pg_oper_ownercheck(oid, GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, NameListToString(opername));
/* pg_operator doesn't have a hard-coded OID, so must look it up */
classoid = get_system_catalog_relid(OperatorRelationName);
/* Call CreateComments() to create/drop the comments */
CreateComments(oid, classoid, 0, comment);
}
/*
* CommentTrigger --
*
* This routine is used to allow a user to provide comments on a
* trigger event. The trigger for commenting is determined by both
* its name and the relation to which it refers. The arguments to this
* function are the trigger name and relation name (merged into a qualified
* name), and the comment to add/drop.
*/
static void
CommentTrigger(List *qualname, char *comment)
{
int nnames;
List *relname;
char *trigname;
RangeVar *rel;
Relation pg_trigger,
relation;
HeapTuple triggertuple;
SysScanDesc scan;
ScanKeyData entry[2];
Oid oid;
/* Separate relname and trig name */
nnames = length(qualname);
if (nnames < 2)
elog(ERROR, "CommentTrigger: must specify relation and trigger");
relname = ltruncate(nnames-1, listCopy(qualname));
trigname = strVal(nth(nnames-1, qualname));
/* Open the owning relation to ensure it won't go away meanwhile */
rel = makeRangeVarFromNameList(relname);
relation = heap_openrv(rel, AccessShareLock);
/* Check object security */
if (!pg_class_ownercheck(RelationGetRelid(relation), GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(relation));
/*
* Fetch the trigger tuple from pg_trigger. There can be only one
* because of the unique index.
*/
pg_trigger = heap_openr(TriggerRelationName, AccessShareLock);
ScanKeyEntryInitialize(&entry[0], 0x0,
Anum_pg_trigger_tgrelid,
F_OIDEQ,
ObjectIdGetDatum(RelationGetRelid(relation)));
ScanKeyEntryInitialize(&entry[1], 0x0,
Anum_pg_trigger_tgname,
F_NAMEEQ,
CStringGetDatum(trigname));
scan = systable_beginscan(pg_trigger, TriggerRelidNameIndex, true,
SnapshotNow, 2, entry);
triggertuple = systable_getnext(scan);
/* If no trigger exists for the relation specified, notify user */
if (!HeapTupleIsValid(triggertuple))
elog(ERROR, "trigger \"%s\" for relation \"%s\" does not exist",
trigname, RelationGetRelationName(relation));
AssertTupleDescHasOid(pg_trigger->rd_att);
oid = HeapTupleGetOid(triggertuple);
systable_endscan(scan);
/* Create the comment with the pg_trigger oid */
CreateComments(oid, RelationGetRelid(pg_trigger), 0, comment);
/* Done, but hold lock on relation */
heap_close(pg_trigger, AccessShareLock);
heap_close(relation, NoLock);
}
/*
* CommentConstraint --
*
* Enable commenting on constraints held within the pg_constraint
* table. A qualified name is required as constraint names are
* unique per relation.
*/
static void
CommentConstraint(List *qualname, char *comment)
{
int nnames;
List *relName;
char *conName;
RangeVar *rel;
Relation pg_constraint,
relation;
HeapTuple tuple;
SysScanDesc scan;
ScanKeyData skey[1];
Oid conOid = InvalidOid;
/* Separate relname and constraint name */
nnames = length(qualname);
if (nnames < 2)
elog(ERROR, "CommentConstraint: must specify relation and constraint");
relName = ltruncate(nnames-1, listCopy(qualname));
conName = strVal(nth(nnames-1, qualname));
/* Open the owning relation to ensure it won't go away meanwhile */
rel = makeRangeVarFromNameList(relName);
relation = heap_openrv(rel, AccessShareLock);
/* Check object security */
if (!pg_class_ownercheck(RelationGetRelid(relation), GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(relation));
/*
* Fetch the constraint tuple from pg_constraint. There may be more than
* one match, because constraints are not required to have unique names;
* if so, error out.
*/
pg_constraint = heap_openr(ConstraintRelationName, AccessShareLock);
ScanKeyEntryInitialize(&skey[0], 0x0,
Anum_pg_constraint_conrelid, F_OIDEQ,
ObjectIdGetDatum(RelationGetRelid(relation)));
scan = systable_beginscan(pg_constraint, ConstraintRelidIndex, true,
SnapshotNow, 1, skey);
while (HeapTupleIsValid(tuple = systable_getnext(scan)))
{
Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
if (strcmp(NameStr(con->conname), conName) == 0)
{
if (OidIsValid(conOid))
elog(ERROR, "Relation \"%s\" has multiple constraints named \"%s\"",
RelationGetRelationName(relation), conName);
conOid = HeapTupleGetOid(tuple);
}
}
systable_endscan(scan);
/* If no constraint exists for the relation specified, notify user */
if (!OidIsValid(conOid))
elog(ERROR, "constraint \"%s\" for relation \"%s\" does not exist",
conName, RelationGetRelationName(relation));
/* Create the comment with the pg_constraint oid */
CreateComments(conOid, RelationGetRelid(pg_constraint), 0, comment);
/* Done, but hold lock on relation */
heap_close(pg_constraint, AccessShareLock);
heap_close(relation, NoLock);
}
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