rewriteDefine.c

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/*-------------------------------------------------------------------------
 *
 * rewriteDefine.c
 *    routines for defining a rewrite rule
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/rewrite/rewriteDefine.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/multixact.h"
#include "access/transam.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/heap.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_rewrite.h"
#include "catalog/storage.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_utilcmd.h"
#include "rewrite/rewriteDefine.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/rewriteSupport.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
#include "utils/tqual.h"


static void checkRuleResultList(List *targetList, TupleDesc resultDesc,
                    bool isSelect);
static bool setRuleCheckAsUser_walker(Node *node, Oid *context);
static void setRuleCheckAsUser_Query(Query *qry, Oid userid);


/*
 * InsertRule -
 *    takes the arguments and inserts them as a row into the system
 *    relation "pg_rewrite"
 */
static Oid
InsertRule(char *rulname,
           int evtype,
           Oid eventrel_oid,
           AttrNumber evslot_index,
           bool evinstead,
           Node *event_qual,
           List *action,
           bool replace)
{
    char       *evqual = nodeToString(event_qual);
    char       *actiontree = nodeToString((Node *) action);
    Datum       values[Natts_pg_rewrite];
    bool        nulls[Natts_pg_rewrite];
    bool        replaces[Natts_pg_rewrite];
    NameData    rname;
    Relation    pg_rewrite_desc;
    HeapTuple   tup,
                oldtup;
    Oid         rewriteObjectId;
    ObjectAddress myself,
                referenced;
    bool        is_update = false;

    /*
     * Set up *nulls and *values arrays
     */
    MemSet(nulls, false, sizeof(nulls));

    namestrcpy(&rname, rulname);
    values[Anum_pg_rewrite_rulename - 1] = NameGetDatum(&rname);
    values[Anum_pg_rewrite_ev_class - 1] = ObjectIdGetDatum(eventrel_oid);
    values[Anum_pg_rewrite_ev_attr - 1] = Int16GetDatum(evslot_index);
    values[Anum_pg_rewrite_ev_type - 1] = CharGetDatum(evtype + '0');
    values[Anum_pg_rewrite_ev_enabled - 1] = CharGetDatum(RULE_FIRES_ON_ORIGIN);
    values[Anum_pg_rewrite_is_instead - 1] = BoolGetDatum(evinstead);
    values[Anum_pg_rewrite_ev_qual - 1] = CStringGetTextDatum(evqual);
    values[Anum_pg_rewrite_ev_action - 1] = CStringGetTextDatum(actiontree);

    /*
     * Ready to store new pg_rewrite tuple
     */
    pg_rewrite_desc = heap_open(RewriteRelationId, RowExclusiveLock);

    /*
     * Check to see if we are replacing an existing tuple
     */
    oldtup = SearchSysCache2(RULERELNAME,
                             ObjectIdGetDatum(eventrel_oid),
                             PointerGetDatum(rulname));

    if (HeapTupleIsValid(oldtup))
    {
        if (!replace)
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_OBJECT),
                     errmsg("rule \"%s\" for relation \"%s\" already exists",
                            rulname, get_rel_name(eventrel_oid))));

        /*
         * When replacing, we don't need to replace every attribute
         */
        MemSet(replaces, false, sizeof(replaces));
        replaces[Anum_pg_rewrite_ev_attr - 1] = true;
        replaces[Anum_pg_rewrite_ev_type - 1] = true;
        replaces[Anum_pg_rewrite_is_instead - 1] = true;
        replaces[Anum_pg_rewrite_ev_qual - 1] = true;
        replaces[Anum_pg_rewrite_ev_action - 1] = true;

        tup = heap_modify_tuple(oldtup, RelationGetDescr(pg_rewrite_desc),
                                values, nulls, replaces);

        simple_heap_update(pg_rewrite_desc, &tup->t_self, tup);

        ReleaseSysCache(oldtup);

        rewriteObjectId = HeapTupleGetOid(tup);
        is_update = true;
    }
    else
    {
        tup = heap_form_tuple(pg_rewrite_desc->rd_att, values, nulls);

        rewriteObjectId = simple_heap_insert(pg_rewrite_desc, tup);
    }

    /* Need to update indexes in either case */
    CatalogUpdateIndexes(pg_rewrite_desc, tup);

    heap_freetuple(tup);

    /* If replacing, get rid of old dependencies and make new ones */
    if (is_update)
        deleteDependencyRecordsFor(RewriteRelationId, rewriteObjectId, false);

    /*
     * Install dependency on rule's relation to ensure it will go away on
     * relation deletion.  If the rule is ON SELECT, make the dependency
     * implicit --- this prevents deleting a view's SELECT rule.  Other kinds
     * of rules can be AUTO.
     */
    myself.classId = RewriteRelationId;
    myself.objectId = rewriteObjectId;
    myself.objectSubId = 0;

    referenced.classId = RelationRelationId;
    referenced.objectId = eventrel_oid;
    referenced.objectSubId = 0;

    recordDependencyOn(&myself, &referenced,
             (evtype == CMD_SELECT) ? DEPENDENCY_INTERNAL : DEPENDENCY_AUTO);

    /*
     * Also install dependencies on objects referenced in action and qual.
     */
    recordDependencyOnExpr(&myself, (Node *) action, NIL,
                           DEPENDENCY_NORMAL);

    if (event_qual != NULL)
    {
        /* Find query containing OLD/NEW rtable entries */
        Query      *qry = (Query *) linitial(action);

        qry = getInsertSelectQuery(qry, NULL);
        recordDependencyOnExpr(&myself, event_qual, qry->rtable,
                               DEPENDENCY_NORMAL);
    }

    /* Post creation hook for new rule */
    InvokeObjectPostCreateHook(RewriteRelationId, rewriteObjectId, 0);

    heap_close(pg_rewrite_desc, RowExclusiveLock);

    return rewriteObjectId;
}

/*
 * DefineRule
 *      Execute a CREATE RULE command.
 */
Oid
DefineRule(RuleStmt *stmt, const char *queryString)
{
    List       *actions;
    Node       *whereClause;
    Oid         relId;

    /* Parse analysis. */
    transformRuleStmt(stmt, queryString, &actions, &whereClause);

    /*
     * Find and lock the relation.  Lock level should match
     * DefineQueryRewrite.
     */
    relId = RangeVarGetRelid(stmt->relation, AccessExclusiveLock, false);

    /* ... and execute */
    return DefineQueryRewrite(stmt->rulename,
                              relId,
                              whereClause,
                              stmt->event,
                              stmt->instead,
                              stmt->replace,
                              actions);
}


/*
 * DefineQueryRewrite
 *      Create a rule
 *
 * This is essentially the same as DefineRule() except that the rule's
 * action and qual have already been passed through parse analysis.
 */
Oid
DefineQueryRewrite(char *rulename,
                   Oid event_relid,
                   Node *event_qual,
                   CmdType event_type,
                   bool is_instead,
                   bool replace,
                   List *action)
{
    Relation    event_relation;
    int         event_attno;
    ListCell   *l;
    Query      *query;
    bool        RelisBecomingView = false;
    Oid         ruleId = InvalidOid;

    /*
     * If we are installing an ON SELECT rule, we had better grab
     * AccessExclusiveLock to ensure no SELECTs are currently running on the
     * event relation. For other types of rules, it would be sufficient to
     * grab ShareRowExclusiveLock to lock out insert/update/delete actions and
     * to ensure that we lock out current CREATE RULE statements; but because
     * of race conditions in access to catalog entries, we can't do that yet.
     *
     * Note that this lock level should match the one used in DefineRule.
     */
    event_relation = heap_open(event_relid, AccessExclusiveLock);

    /*
     * Verify relation is of a type that rules can sensibly be applied to.
     */
    if (event_relation->rd_rel->relkind != RELKIND_RELATION &&
        event_relation->rd_rel->relkind != RELKIND_MATVIEW &&
        event_relation->rd_rel->relkind != RELKIND_VIEW)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table or view",
                        RelationGetRelationName(event_relation))));

    if (!allowSystemTableMods && IsSystemRelation(event_relation))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        RelationGetRelationName(event_relation))));

    /*
     * Check user has permission to apply rules to this relation.
     */
    if (!pg_class_ownercheck(event_relid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                       RelationGetRelationName(event_relation));

    /*
     * No rule actions that modify OLD or NEW
     */
    foreach(l, action)
    {
        query = (Query *) lfirst(l);
        if (query->resultRelation == 0)
            continue;
        /* Don't be fooled by INSERT/SELECT */
        if (query != getInsertSelectQuery(query, NULL))
            continue;
        if (query->resultRelation == PRS2_OLD_VARNO)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rule actions on OLD are not implemented"),
                     errhint("Use views or triggers instead.")));
        if (query->resultRelation == PRS2_NEW_VARNO)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rule actions on NEW are not implemented"),
                     errhint("Use triggers instead.")));
    }

    if (event_type == CMD_SELECT)
    {
        /*
         * Rules ON SELECT are restricted to view definitions
         *
         * So there cannot be INSTEAD NOTHING, ...
         */
        if (list_length(action) == 0)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
               errmsg("INSTEAD NOTHING rules on SELECT are not implemented"),
                     errhint("Use views instead.")));

        /*
         * ... there cannot be multiple actions, ...
         */
        if (list_length(action) > 1)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("multiple actions for rules on SELECT are not implemented")));

        /*
         * ... the one action must be a SELECT, ...
         */
        query = (Query *) linitial(action);
        if (!is_instead ||
            query->commandType != CMD_SELECT ||
            query->utilityStmt != NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("rules on SELECT must have action INSTEAD SELECT")));

        /*
         * ... it cannot contain data-modifying WITH ...
         */
        if (query->hasModifyingCTE)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("rules on SELECT must not contain data-modifying statements in WITH")));

        /*
         * ... there can be no rule qual, ...
         */
        if (event_qual != NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("event qualifications are not implemented for rules on SELECT")));

        /*
         * ... the targetlist of the SELECT action must exactly match the
         * event relation, ...
         */
        checkRuleResultList(query->targetList,
                            RelationGetDescr(event_relation),
                            true);

        /*
         * ... there must not be another ON SELECT rule already ...
         */
        if (!replace && event_relation->rd_rules != NULL)
        {
            int         i;

            for (i = 0; i < event_relation->rd_rules->numLocks; i++)
            {
                RewriteRule *rule;

                rule = event_relation->rd_rules->rules[i];
                if (rule->event == CMD_SELECT)
                    ereport(ERROR,
                          (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                           errmsg("\"%s\" is already a view",
                                  RelationGetRelationName(event_relation))));
            }
        }

        /*
         * ... and finally the rule must be named _RETURN.
         */
        if (strcmp(rulename, ViewSelectRuleName) != 0)
        {
            /*
             * In versions before 7.3, the expected name was _RETviewname. For
             * backwards compatibility with old pg_dump output, accept that
             * and silently change it to _RETURN.  Since this is just a quick
             * backwards-compatibility hack, limit the number of characters
             * checked to a few less than NAMEDATALEN; this saves having to
             * worry about where a multibyte character might have gotten
             * truncated.
             */
            if (strncmp(rulename, "_RET", 4) != 0 ||
                strncmp(rulename + 4, RelationGetRelationName(event_relation),
                        NAMEDATALEN - 4 - 4) != 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                         errmsg("view rule for \"%s\" must be named \"%s\"",
                                RelationGetRelationName(event_relation),
                                ViewSelectRuleName)));
            rulename = pstrdup(ViewSelectRuleName);
        }

        /*
         * Are we converting a relation to a view?
         *
         * If so, check that the relation is empty because the storage for the
         * relation is going to be deleted.  Also insist that the rel not have
         * any triggers, indexes, or child tables.  (Note: these tests are too
         * strict, because they will reject relations that once had such but
         * don't anymore.  But we don't really care, because this whole
         * business of converting relations to views is just a kluge to allow
         * dump/reload of views that participate in circular dependencies.)
         */
        if (event_relation->rd_rel->relkind != RELKIND_VIEW &&
            event_relation->rd_rel->relkind != RELKIND_MATVIEW)
        {
            HeapScanDesc scanDesc;

            scanDesc = heap_beginscan(event_relation, SnapshotNow, 0, NULL);
            if (heap_getnext(scanDesc, ForwardScanDirection) != NULL)
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("could not convert table \"%s\" to a view because it is not empty",
                                RelationGetRelationName(event_relation))));
            heap_endscan(scanDesc);

            if (event_relation->rd_rel->relhastriggers)
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("could not convert table \"%s\" to a view because it has triggers",
                                RelationGetRelationName(event_relation)),
                         errhint("In particular, the table cannot be involved in any foreign key relationships.")));

            if (event_relation->rd_rel->relhasindex)
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("could not convert table \"%s\" to a view because it has indexes",
                                RelationGetRelationName(event_relation))));

            if (event_relation->rd_rel->relhassubclass)
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("could not convert table \"%s\" to a view because it has child tables",
                                RelationGetRelationName(event_relation))));

            RelisBecomingView = true;
        }
    }
    else
    {
        /*
         * For non-SELECT rules, a RETURNING list can appear in at most one of
         * the actions ... and there can't be any RETURNING list at all in a
         * conditional or non-INSTEAD rule.  (Actually, there can be at most
         * one RETURNING list across all rules on the same event, but it seems
         * best to enforce that at rule expansion time.)  If there is a
         * RETURNING list, it must match the event relation.
         */
        bool        haveReturning = false;

        foreach(l, action)
        {
            query = (Query *) lfirst(l);

            if (!query->returningList)
                continue;
            if (haveReturning)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                  errmsg("cannot have multiple RETURNING lists in a rule")));
            haveReturning = true;
            if (event_qual != NULL)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("RETURNING lists are not supported in conditional rules")));
            if (!is_instead)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("RETURNING lists are not supported in non-INSTEAD rules")));
            checkRuleResultList(query->returningList,
                                RelationGetDescr(event_relation),
                                false);
        }
    }

    /*
     * This rule is allowed - prepare to install it.
     */
    event_attno = -1;

    /* discard rule if it's null action and not INSTEAD; it's a no-op */
    if (action != NIL || is_instead)
    {
        ruleId = InsertRule(rulename,
                            event_type,
                            event_relid,
                            event_attno,
                            is_instead,
                            event_qual,
                            action,
                            replace);

        /*
         * Set pg_class 'relhasrules' field TRUE for event relation.
         *
         * Important side effect: an SI notice is broadcast to force all
         * backends (including me!) to update relcache entries with the new
         * rule.
         */
        SetRelationRuleStatus(event_relid, true);
    }

    /* ---------------------------------------------------------------------
     * If the relation is becoming a view:
     * - delete the associated storage files
     * - get rid of any system attributes in pg_attribute; a view shouldn't
     *   have any of those
     * - remove the toast table; there is no need for it anymore, and its
     *   presence would make vacuum slightly more complicated
     * - set relkind to RELKIND_VIEW, and adjust other pg_class fields
     *   to be appropriate for a view
     *
     * NB: we had better have AccessExclusiveLock to do this ...
     * ---------------------------------------------------------------------
     */
    if (RelisBecomingView)
    {
        Relation    relationRelation;
        Oid         toastrelid;
        HeapTuple   classTup;
        Form_pg_class classForm;

        relationRelation = heap_open(RelationRelationId, RowExclusiveLock);
        toastrelid = event_relation->rd_rel->reltoastrelid;

        /* drop storage while table still looks like a table  */
        RelationDropStorage(event_relation);
        DeleteSystemAttributeTuples(event_relid);

        /*
         * Drop the toast table if any.  (This won't take care of updating
         * the toast fields in the relation's own pg_class entry; we handle
         * that below.)
         */
        if (OidIsValid(toastrelid))
        {
            ObjectAddress toastobject;

            /*
             * Delete the dependency of the toast relation on the main
             * relation so we can drop the former without dropping the latter.
             */
            deleteDependencyRecordsFor(RelationRelationId, toastrelid,
                                       false);

            /* Make deletion of dependency record visible */
            CommandCounterIncrement();

            /* Now drop toast table, including its index */
            toastobject.classId = RelationRelationId;
            toastobject.objectId = toastrelid;
            toastobject.objectSubId = 0;
            performDeletion(&toastobject, DROP_RESTRICT,
                            PERFORM_DELETION_INTERNAL);
        }

        /*
         * SetRelationRuleStatus may have updated the pg_class row, so we must
         * advance the command counter before trying to update it again.
         */
        CommandCounterIncrement();

        /*
         * Fix pg_class entry to look like a normal view's, including setting
         * the correct relkind and removal of reltoastrelid/reltoastidxid of
         * the toast table we potentially removed above.
         */
        classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(event_relid));
        if (!HeapTupleIsValid(classTup))
            elog(ERROR, "cache lookup failed for relation %u", event_relid);
        classForm = (Form_pg_class) GETSTRUCT(classTup);

        classForm->reltablespace = InvalidOid;
        classForm->relpages = 0;
        classForm->reltuples = 0;
        classForm->relallvisible = 0;
        classForm->reltoastrelid = InvalidOid;
        classForm->reltoastidxid = InvalidOid;
        classForm->relhasindex = false;
        classForm->relkind = RELKIND_VIEW;
        classForm->relhasoids = false;
        classForm->relhaspkey = false;
        classForm->relfrozenxid = InvalidTransactionId;
        classForm->relminmxid = InvalidMultiXactId;

        simple_heap_update(relationRelation, &classTup->t_self, classTup);
        CatalogUpdateIndexes(relationRelation, classTup);

        heap_freetuple(classTup);
        heap_close(relationRelation, RowExclusiveLock);
    }

    /* Close rel, but keep lock till commit... */
    heap_close(event_relation, NoLock);

    return ruleId;
}

/*
 * checkRuleResultList
 *      Verify that targetList produces output compatible with a tupledesc
 *
 * The targetList might be either a SELECT targetlist, or a RETURNING list;
 * isSelect tells which.  (This is mostly used for choosing error messages,
 * but also we don't enforce column name matching for RETURNING.)
 */
static void
checkRuleResultList(List *targetList, TupleDesc resultDesc, bool isSelect)
{
    ListCell   *tllist;
    int         i;

    i = 0;
    foreach(tllist, targetList)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(tllist);
        int32       tletypmod;
        Form_pg_attribute attr;
        char       *attname;

        /* resjunk entries may be ignored */
        if (tle->resjunk)
            continue;
        i++;
        if (i > resultDesc->natts)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     isSelect ?
                   errmsg("SELECT rule's target list has too many entries") :
                     errmsg("RETURNING list has too many entries")));

        attr = resultDesc->attrs[i - 1];
        attname = NameStr(attr->attname);

        /*
         * Disallow dropped columns in the relation.  This won't happen in the
         * cases we actually care about (namely creating a view via CREATE
         * TABLE then CREATE RULE, or adding a RETURNING rule to a view).
         * Trying to cope with it is much more trouble than it's worth,
         * because we'd have to modify the rule to insert dummy NULLs at the
         * right positions.
         */
        if (attr->attisdropped)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cannot convert relation containing dropped columns to view")));

        if (isSelect && strcmp(tle->resname, attname) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("SELECT rule's target entry %d has different column name from \"%s\"", i, attname)));

        if (attr->atttypid != exprType((Node *) tle->expr))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     isSelect ?
                     errmsg("SELECT rule's target entry %d has different type from column \"%s\"",
                            i, attname) :
                     errmsg("RETURNING list's entry %d has different type from column \"%s\"",
                            i, attname)));

        /*
         * Allow typmods to be different only if one of them is -1, ie,
         * "unspecified".  This is necessary for cases like "numeric", where
         * the table will have a filled-in default length but the select
         * rule's expression will probably have typmod = -1.
         */
        tletypmod = exprTypmod((Node *) tle->expr);
        if (attr->atttypmod != tletypmod &&
            attr->atttypmod != -1 && tletypmod != -1)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     isSelect ?
                     errmsg("SELECT rule's target entry %d has different size from column \"%s\"",
                            i, attname) :
                     errmsg("RETURNING list's entry %d has different size from column \"%s\"",
                            i, attname)));
    }

    if (i != resultDesc->natts)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 isSelect ?
                 errmsg("SELECT rule's target list has too few entries") :
                 errmsg("RETURNING list has too few entries")));
}

/*
 * setRuleCheckAsUser
 *      Recursively scan a query or expression tree and set the checkAsUser
 *      field to the given userid in all rtable entries.
 *
 * Note: for a view (ON SELECT rule), the checkAsUser field of the OLD
 * RTE entry will be overridden when the view rule is expanded, and the
 * checkAsUser field of the NEW entry is irrelevant because that entry's
 * requiredPerms bits will always be zero.  However, for other types of rules
 * it's important to set these fields to match the rule owner.  So we just set
 * them always.
 */
void
setRuleCheckAsUser(Node *node, Oid userid)
{
    (void) setRuleCheckAsUser_walker(node, &userid);
}

static bool
setRuleCheckAsUser_walker(Node *node, Oid *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Query))
    {
        setRuleCheckAsUser_Query((Query *) node, *context);
        return false;
    }
    return expression_tree_walker(node, setRuleCheckAsUser_walker,
                                  (void *) context);
}

static void
setRuleCheckAsUser_Query(Query *qry, Oid userid)
{
    ListCell   *l;

    /* Set all the RTEs in this query node */
    foreach(l, qry->rtable)
    {
        RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

        if (rte->rtekind == RTE_SUBQUERY)
        {
            /* Recurse into subquery in FROM */
            setRuleCheckAsUser_Query(rte->subquery, userid);
        }
        else
            rte->checkAsUser = userid;
    }

    /* Recurse into subquery-in-WITH */
    foreach(l, qry->cteList)
    {
        CommonTableExpr *cte = (CommonTableExpr *) lfirst(l);

        setRuleCheckAsUser_Query((Query *) cte->ctequery, userid);
    }

    /* If there are sublinks, search for them and process their RTEs */
    if (qry->hasSubLinks)
        query_tree_walker(qry, setRuleCheckAsUser_walker, (void *) &userid,
                          QTW_IGNORE_RC_SUBQUERIES);
}


/*
 * Change the firing semantics of an existing rule.
 */
void
EnableDisableRule(Relation rel, const char *rulename,
                  char fires_when)
{
    Relation    pg_rewrite_desc;
    Oid         owningRel = RelationGetRelid(rel);
    Oid         eventRelationOid;
    HeapTuple   ruletup;
    bool        changed = false;

    /*
     * Find the rule tuple to change.
     */
    pg_rewrite_desc = heap_open(RewriteRelationId, RowExclusiveLock);
    ruletup = SearchSysCacheCopy2(RULERELNAME,
                                  ObjectIdGetDatum(owningRel),
                                  PointerGetDatum(rulename));
    if (!HeapTupleIsValid(ruletup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("rule \"%s\" for relation \"%s\" does not exist",
                        rulename, get_rel_name(owningRel))));

    /*
     * Verify that the user has appropriate permissions.
     */
    eventRelationOid = ((Form_pg_rewrite) GETSTRUCT(ruletup))->ev_class;
    Assert(eventRelationOid == owningRel);
    if (!pg_class_ownercheck(eventRelationOid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                       get_rel_name(eventRelationOid));

    /*
     * Change ev_enabled if it is different from the desired new state.
     */
    if (DatumGetChar(((Form_pg_rewrite) GETSTRUCT(ruletup))->ev_enabled) !=
        fires_when)
    {
        ((Form_pg_rewrite) GETSTRUCT(ruletup))->ev_enabled =
            CharGetDatum(fires_when);
        simple_heap_update(pg_rewrite_desc, &ruletup->t_self, ruletup);

        /* keep system catalog indexes current */
        CatalogUpdateIndexes(pg_rewrite_desc, ruletup);

        changed = true;
    }

    InvokeObjectPostAlterHook(RewriteRelationId,
                              HeapTupleGetOid(ruletup), 0);

    heap_freetuple(ruletup);
    heap_close(pg_rewrite_desc, RowExclusiveLock);

    /*
     * If we changed anything, broadcast a SI inval message to force each
     * backend (including our own!) to rebuild relation's relcache entry.
     * Otherwise they will fail to apply the change promptly.
     */
    if (changed)
        CacheInvalidateRelcache(rel);
}


/*
 * Perform permissions and integrity checks before acquiring a relation lock.
 */
static void
RangeVarCallbackForRenameRule(const RangeVar *rv, Oid relid, Oid oldrelid,
                              void *arg)
{
    HeapTuple   tuple;
    Form_pg_class form;

    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        return;                 /* concurrently dropped */
    form = (Form_pg_class) GETSTRUCT(tuple);

    /* only tables and views can have rules */
    if (form->relkind != RELKIND_RELATION && form->relkind != RELKIND_VIEW)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table or view", rv->relname)));

    if (!allowSystemTableMods && IsSystemClass(form))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        rv->relname)));

    /* you must own the table to rename one of its rules */
    if (!pg_class_ownercheck(relid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS, rv->relname);

    ReleaseSysCache(tuple);
}

/*
 * Rename an existing rewrite rule.
 */
Oid
RenameRewriteRule(RangeVar *relation, const char *oldName,
                  const char *newName)
{
    Oid         relid;
    Relation    targetrel;
    Relation    pg_rewrite_desc;
    HeapTuple   ruletup;
    Form_pg_rewrite ruleform;
    Oid         ruleOid;

    /*
     * Look up name, check permissions, and acquire lock (which we will NOT
     * release until end of transaction).
     */
    relid = RangeVarGetRelidExtended(relation, AccessExclusiveLock,
                                     false, false,
                                     RangeVarCallbackForRenameRule,
                                     NULL);

    /* Have lock already, so just need to build relcache entry. */
    targetrel = relation_open(relid, NoLock);

    /* Prepare to modify pg_rewrite */
    pg_rewrite_desc = heap_open(RewriteRelationId, RowExclusiveLock);

    /* Fetch the rule's entry (it had better exist) */
    ruletup = SearchSysCacheCopy2(RULERELNAME,
                                  ObjectIdGetDatum(relid),
                                  PointerGetDatum(oldName));
    if (!HeapTupleIsValid(ruletup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("rule \"%s\" for relation \"%s\" does not exist",
                        oldName, RelationGetRelationName(targetrel))));
    ruleform = (Form_pg_rewrite) GETSTRUCT(ruletup);
    ruleOid = HeapTupleGetOid(ruletup);

    /* rule with the new name should not already exist */
    if (IsDefinedRewriteRule(relid, newName))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("rule \"%s\" for relation \"%s\" already exists",
                        newName, RelationGetRelationName(targetrel))));

    /*
     * We disallow renaming ON SELECT rules, because they should always be
     * named "_RETURN".
     */
    if (ruleform->ev_type == CMD_SELECT + '0')
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("renaming an ON SELECT rule is not allowed")));

    /* OK, do the update */
    namestrcpy(&(ruleform->rulename), newName);

    simple_heap_update(pg_rewrite_desc, &ruletup->t_self, ruletup);

    /* keep system catalog indexes current */
    CatalogUpdateIndexes(pg_rewrite_desc, ruletup);

    heap_freetuple(ruletup);
    heap_close(pg_rewrite_desc, RowExclusiveLock);

    /*
     * Invalidate relation's relcache entry so that other backends (and this
     * one too!) are sent SI message to make them rebuild relcache entries.
     * (Ideally this should happen automatically...)
     */
    CacheInvalidateRelcache(targetrel);

    /*
     * Close rel, but keep exclusive lock!
     */
    relation_close(targetrel, NoLock);

    return ruleOid;
}