src/backend/commands/view.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * view.c
   4  *        use rewrite rules to construct views
   5  *
   6  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        $Header: /cvsroot/pgsql/src/backend/commands/view.c,v 1.71 2002/09/04 20:31:17 momjian Exp $
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 #include "postgres.h"
  16
  17 #include "access/heapam.h"
  18 #include "catalog/dependency.h"
  19 #include "catalog/namespace.h"
  20 #include "commands/tablecmds.h"
  21 #include "commands/view.h"
  22 #include "miscadmin.h"
  23 #include "nodes/makefuncs.h"
  24 #include "parser/parse_relation.h"
  25 #include "rewrite/rewriteDefine.h"
  26 #include "rewrite/rewriteManip.h"
  27 #include "rewrite/rewriteSupport.h"
  28 #include "utils/acl.h"
  29 #include "utils/lsyscache.h"
  30
  31
  32 static void checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc);
  33
  34
  35 /*---------------------------------------------------------------------
  36  * DefineVirtualRelation
  37  *
  38  * Create the "view" relation. `DefineRelation' does all the work,
  39  * we just provide the correct arguments ... at least when we're
  40  * creating a view.  If we're updating an existing view, we have to
  41  * work harder.
  42  *---------------------------------------------------------------------
  43  */
  44 static Oid
  45 DefineVirtualRelation(const RangeVar *relation, List *tlist, bool replace)
  46 {
  47         Oid                     viewOid,
  48                                 namespaceId;
  49         CreateStmt *createStmt = makeNode(CreateStmt);
  50         List       *attrList,
  51                            *t;
  52
  53         /*
  54          * create a list of ColumnDef nodes based on the names and types of
  55          * the (non-junk) targetlist items from the view's SELECT list.
  56          */
  57         attrList = NIL;
  58         foreach(t, tlist)
  59         {
  60                 TargetEntry *entry = lfirst(t);
  61                 Resdom     *res = entry->resdom;
  62
  63                 if (!res->resjunk)
  64                 {
  65                         ColumnDef  *def = makeNode(ColumnDef);
  66                         TypeName   *typename = makeNode(TypeName);
  67
  68                         def->colname = pstrdup(res->resname);
  69
  70                         typename->typeid = res->restype;
  71                         typename->typmod = res->restypmod;
  72                         def->typename = typename;
  73
  74                         def->is_inherited = false;
  75                         def->is_not_null = false;
  76                         def->raw_default = NULL;
  77                         def->cooked_default = NULL;
  78                         def->constraints = NIL;
  79                         def->support = NULL;
  80
  81                         attrList = lappend(attrList, def);
  82                 }
  83         }
  84
  85         if (attrList == NIL)
  86                 elog(ERROR, "attempted to define virtual relation with no attrs");
  87
  88         /*
  89          * Check to see if we want to replace an existing view.
  90          */
  91         namespaceId = RangeVarGetCreationNamespace(relation);
  92         viewOid = get_relname_relid(relation->relname, namespaceId);
  93
  94         if (OidIsValid(viewOid) && replace)
  95         {
  96                 Relation        rel;
  97                 TupleDesc       descriptor;
  98
  99                 /*
 100                  * Yes.  Get exclusive lock on the existing view ...
 101                  */
 102                 rel = relation_open(viewOid, AccessExclusiveLock);
 103
 104                 /*
 105                  * Make sure it *is* a view, and do permissions checks.
 106                  */
 107                 if (rel->rd_rel->relkind != RELKIND_VIEW)
 108                         elog(ERROR, "%s is not a view",
 109                                  RelationGetRelationName(rel));
 110
 111                 if (!pg_class_ownercheck(viewOid, GetUserId()))
 112                         aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(rel));
 113
 114                 /*
 115                  * Create a tuple descriptor to compare against the existing view,
 116                  * and verify it matches.
 117                  */
 118                 descriptor = BuildDescForRelation(attrList);
 119                 checkViewTupleDesc(descriptor, rel->rd_att);
 120
 121                 /*
 122                  * Seems okay, so return the OID of the pre-existing view.
 123                  */
 124                 relation_close(rel, NoLock);    /* keep the lock! */
 125
 126                 return viewOid;
 127         }
 128         else
 129         {
 130                 /*
 131                  * now create the parameters for keys/inheritance etc. All of them
 132                  * are nil...
 133                  */
 134                 createStmt->relation = (RangeVar *) relation;
 135                 createStmt->tableElts = attrList;
 136                 createStmt->inhRelations = NIL;
 137                 createStmt->constraints = NIL;
 138                 createStmt->hasoids = false;
 139
 140                 /*
 141                  * finally create the relation (this will error out if there's an
 142                  * existing view, so we don't need more code to complain if
 143                  * "replace" is false).
 144                  */
 145                 return DefineRelation(createStmt, RELKIND_VIEW);
 146         }
 147 }
 148
 149 /*
 150  * Verify that tupledesc associated with proposed new view definition
 151  * matches tupledesc of old view.  This is basically a cut-down version
 152  * of equalTupleDescs(), with code added to generate specific complaints.
 153  */
 154 static void
 155 checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
 156 {
 157         int                     i;
 158
 159         if (newdesc->natts != olddesc->natts)
 160                 elog(ERROR, "Cannot change number of columns in view");
 161         /* we can ignore tdhasoid */
 162
 163         for (i = 0; i < newdesc->natts; i++)
 164         {
 165                 Form_pg_attribute newattr = newdesc->attrs[i];
 166                 Form_pg_attribute oldattr = olddesc->attrs[i];
 167
 168                 /* XXX not right, but we don't support DROP COL on view anyway */
 169                 if (newattr->attisdropped != oldattr->attisdropped)
 170                         elog(ERROR, "Cannot change number of columns in view");
 171
 172                 if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
 173                         elog(ERROR, "Cannot change name of view column \"%s\"",
 174                                  NameStr(oldattr->attname));
 175                 /* XXX would it be safe to allow atttypmod to change?  Not sure */
 176                 if (newattr->atttypid != oldattr->atttypid ||
 177                         newattr->atttypmod != oldattr->atttypmod)
 178                         elog(ERROR, "Cannot change datatype of view column \"%s\"",
 179                                  NameStr(oldattr->attname));
 180                 /* We can ignore the remaining attributes of an attribute... */
 181         }
 182
 183         /*
 184          * We ignore the constraint fields.  The new view desc can't have any
 185          * constraints, and the only ones that could be on the old view are
 186          * defaults, which we are happy to leave in place.
 187          */
 188 }
 189
 190 static RuleStmt *
 191 FormViewRetrieveRule(const RangeVar *view, Query *viewParse, bool replace)
 192 {
 193         RuleStmt   *rule;
 194
 195         /*
 196          * Create a RuleStmt that corresponds to the suitable rewrite rule
 197          * args for DefineQueryRewrite();
 198          */
 199         rule = makeNode(RuleStmt);
 200         rule->relation = copyObject((RangeVar *) view);
 201         rule->rulename = pstrdup(ViewSelectRuleName);
 202         rule->whereClause = NULL;
 203         rule->event = CMD_SELECT;
 204         rule->instead = true;
 205         rule->actions = makeList1(viewParse);
 206         rule->replace = replace;
 207
 208         return rule;
 209 }
 210
 211 static void
 212 DefineViewRules(const RangeVar *view, Query *viewParse, bool replace)
 213 {
 214         RuleStmt   *retrieve_rule;
 215
 216 #ifdef NOTYET
 217         RuleStmt   *replace_rule;
 218         RuleStmt   *append_rule;
 219         RuleStmt   *delete_rule;
 220 #endif
 221
 222         retrieve_rule = FormViewRetrieveRule(view, viewParse, replace);
 223
 224 #ifdef NOTYET
 225         replace_rule = FormViewReplaceRule(view, viewParse);
 226         append_rule = FormViewAppendRule(view, viewParse);
 227         delete_rule = FormViewDeleteRule(view, viewParse);
 228 #endif
 229
 230         DefineQueryRewrite(retrieve_rule);
 231
 232 #ifdef NOTYET
 233         DefineQueryRewrite(replace_rule);
 234         DefineQueryRewrite(append_rule);
 235         DefineQueryRewrite(delete_rule);
 236 #endif
 237
 238 }
 239
 240 /*---------------------------------------------------------------
 241  * UpdateRangeTableOfViewParse
 242  *
 243  * Update the range table of the given parsetree.
 244  * This update consists of adding two new entries IN THE BEGINNING
 245  * of the range table (otherwise the rule system will die a slow,
 246  * horrible and painful death, and we do not want that now, do we?)
 247  * one for the OLD relation and one for the NEW one (both of
 248  * them refer in fact to the "view" relation).
 249  *
 250  * Of course we must also increase the 'varnos' of all the Var nodes
 251  * by 2...
 252  *
 253  * These extra RT entries are not actually used in the query,
 254  * except for run-time permission checking.
 255  *---------------------------------------------------------------
 256  */
 257 static Query *
 258 UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
 259 {
 260         List       *new_rt;
 261         RangeTblEntry *rt_entry1,
 262                            *rt_entry2;
 263
 264         /*
 265          * Make a copy of the given parsetree.  It's not so much that we don't
 266          * want to scribble on our input, it's that the parser has a bad habit
 267          * of outputting multiple links to the same subtree for constructs
 268          * like BETWEEN, and we mustn't have OffsetVarNodes increment the
 269          * varno of a Var node twice.  copyObject will expand any
 270          * multiply-referenced subtree into multiple copies.
 271          */
 272         viewParse = (Query *) copyObject(viewParse);
 273
 274         /*
 275          * Create the 2 new range table entries and form the new range
 276          * table... OLD first, then NEW....
 277          */
 278         rt_entry1 = addRangeTableEntryForRelation(NULL, viewOid,
 279                                                                                           makeAlias("*OLD*", NIL),
 280                                                                                           false, false);
 281         rt_entry2 = addRangeTableEntryForRelation(NULL, viewOid,
 282                                                                                           makeAlias("*NEW*", NIL),
 283                                                                                           false, false);
 284         /* Must override addRangeTableEntry's default access-check flags */
 285         rt_entry1->checkForRead = false;
 286         rt_entry2->checkForRead = false;
 287
 288         new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));
 289
 290         viewParse->rtable = new_rt;
 291
 292         /*
 293          * Now offset all var nodes by 2, and jointree RT indexes too.
 294          */
 295         OffsetVarNodes((Node *) viewParse, 2, 0);
 296
 297         return viewParse;
 298 }
 299
 300 /*-------------------------------------------------------------------
 301  * DefineView
 302  *
 303  *              - takes a "viewname", "parsetree" pair and then
 304  *              1)              construct the "virtual" relation
 305  *              2)              commit the command but NOT the transaction,
 306  *                              so that the relation exists
 307  *                              before the rules are defined.
 308  *              2)              define the "n" rules specified in the PRS2 paper
 309  *                              over the "virtual" relation
 310  *-------------------------------------------------------------------
 311  */
 312 void
 313 DefineView(const RangeVar *view, Query *viewParse, bool replace)
 314 {
 315         Oid                     viewOid;
 316
 317         /*
 318          * Create the view relation
 319          *
 320          * NOTE: if it already exists and replace is false, the xact will be
 321          * aborted.
 322          */
 323
 324         viewOid = DefineVirtualRelation(view, viewParse->targetList, replace);
 325
 326         /*
 327          * The relation we have just created is not visible to any other
 328          * commands running with the same transaction & command id. So,
 329          * increment the command id counter (but do NOT pfree any memory!!!!)
 330          */
 331         CommandCounterIncrement();
 332
 333         /*
 334          * The range table of 'viewParse' does not contain entries for the
 335          * "OLD" and "NEW" relations. So... add them!
 336          */
 337         viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);
 338
 339         /*
 340          * Now create the rules associated with the view.
 341          */
 342         DefineViewRules(view, viewParse, replace);
 343 }
 344
 345 /*
 346  * RemoveView
 347  *
 348  * Remove a view given its name
 349  *
 350  * We just have to drop the relation; the associated rules will be
 351  * cleaned up automatically.
 352  */
 353 void
 354 RemoveView(const RangeVar *view, DropBehavior behavior)
 355 {
 356         Oid                     viewOid;
 357         ObjectAddress object;
 358
 359         viewOid = RangeVarGetRelid(view, false);
 360
 361         object.classId = RelOid_pg_class;
 362         object.objectId = viewOid;
 363         object.objectSubId = 0;
 364
 365         performDeletion(&object, behavior);
 366 }