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 1.74 2003/07/20 21:56:34 tgl 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->inhcount = 0;
  75                         def->is_local = true;
  76                         def->is_not_null = false;
  77                         def->raw_default = NULL;
  78                         def->cooked_default = NULL;
  79                         def->constraints = NIL;
  80                         def->support = NULL;
  81
  82                         attrList = lappend(attrList, def);
  83                 }
  84         }
  85
  86         if (attrList == NIL)
  87                 ereport(ERROR,
  88                                 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
  89                                  errmsg("view must have at least one attribute")));
  90
  91         /*
  92          * Check to see if we want to replace an existing view.
  93          */
  94         namespaceId = RangeVarGetCreationNamespace(relation);
  95         viewOid = get_relname_relid(relation->relname, namespaceId);
  96
  97         if (OidIsValid(viewOid) && replace)
  98         {
  99                 Relation        rel;
 100                 TupleDesc       descriptor;
 101
 102                 /*
 103                  * Yes.  Get exclusive lock on the existing view ...
 104                  */
 105                 rel = relation_open(viewOid, AccessExclusiveLock);
 106
 107                 /*
 108                  * Make sure it *is* a view, and do permissions checks.
 109                  */
 110                 if (rel->rd_rel->relkind != RELKIND_VIEW)
 111                         ereport(ERROR,
 112                                         (errcode(ERRCODE_WRONG_OBJECT_TYPE),
 113                                          errmsg("\"%s\" is not a view",
 114                                                         RelationGetRelationName(rel))));
 115
 116                 if (!pg_class_ownercheck(viewOid, GetUserId()))
 117                         aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(rel));
 118
 119                 /*
 120                  * Create a tuple descriptor to compare against the existing view,
 121                  * and verify it matches.
 122                  */
 123                 descriptor = BuildDescForRelation(attrList);
 124                 checkViewTupleDesc(descriptor, rel->rd_att);
 125
 126                 /*
 127                  * Seems okay, so return the OID of the pre-existing view.
 128                  */
 129                 relation_close(rel, NoLock);    /* keep the lock! */
 130
 131                 return viewOid;
 132         }
 133         else
 134         {
 135                 /*
 136                  * now create the parameters for keys/inheritance etc. All of them
 137                  * are nil...
 138                  */
 139                 createStmt->relation = (RangeVar *) relation;
 140                 createStmt->tableElts = attrList;
 141                 createStmt->inhRelations = NIL;
 142                 createStmt->constraints = NIL;
 143                 createStmt->hasoids = false;
 144                 createStmt->oncommit = ONCOMMIT_NOOP;
 145
 146                 /*
 147                  * finally create the relation (this will error out if there's an
 148                  * existing view, so we don't need more code to complain if
 149                  * "replace" is false).
 150                  */
 151                 return DefineRelation(createStmt, RELKIND_VIEW);
 152         }
 153 }
 154
 155 /*
 156  * Verify that tupledesc associated with proposed new view definition
 157  * matches tupledesc of old view.  This is basically a cut-down version
 158  * of equalTupleDescs(), with code added to generate specific complaints.
 159  */
 160 static void
 161 checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
 162 {
 163         int                     i;
 164
 165         if (newdesc->natts != olddesc->natts)
 166                 ereport(ERROR,
 167                                 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 168                                  errmsg("cannot change number of columns in view")));
 169         /* we can ignore tdhasoid */
 170
 171         for (i = 0; i < newdesc->natts; i++)
 172         {
 173                 Form_pg_attribute newattr = newdesc->attrs[i];
 174                 Form_pg_attribute oldattr = olddesc->attrs[i];
 175
 176                 /* XXX not right, but we don't support DROP COL on view anyway */
 177                 if (newattr->attisdropped != oldattr->attisdropped)
 178                         ereport(ERROR,
 179                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 180                                          errmsg("cannot change number of columns in view")));
 181
 182                 if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
 183                         ereport(ERROR,
 184                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 185                                          errmsg("cannot change name of view column \"%s\"",
 186                                                         NameStr(oldattr->attname))));
 187                 /* XXX would it be safe to allow atttypmod to change?  Not sure */
 188                 if (newattr->atttypid != oldattr->atttypid ||
 189                         newattr->atttypmod != oldattr->atttypmod)
 190                         ereport(ERROR,
 191                                         (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 192                                          errmsg("cannot change datatype of view column \"%s\"",
 193                                                         NameStr(oldattr->attname))));
 194                 /* We can ignore the remaining attributes of an attribute... */
 195         }
 196
 197         /*
 198          * We ignore the constraint fields.  The new view desc can't have any
 199          * constraints, and the only ones that could be on the old view are
 200          * defaults, which we are happy to leave in place.
 201          */
 202 }
 203
 204 static RuleStmt *
 205 FormViewRetrieveRule(const RangeVar *view, Query *viewParse, bool replace)
 206 {
 207         RuleStmt   *rule;
 208
 209         /*
 210          * Create a RuleStmt that corresponds to the suitable rewrite rule
 211          * args for DefineQueryRewrite();
 212          */
 213         rule = makeNode(RuleStmt);
 214         rule->relation = copyObject((RangeVar *) view);
 215         rule->rulename = pstrdup(ViewSelectRuleName);
 216         rule->whereClause = NULL;
 217         rule->event = CMD_SELECT;
 218         rule->instead = true;
 219         rule->actions = makeList1(viewParse);
 220         rule->replace = replace;
 221
 222         return rule;
 223 }
 224
 225 static void
 226 DefineViewRules(const RangeVar *view, Query *viewParse, bool replace)
 227 {
 228         RuleStmt   *retrieve_rule;
 229
 230 #ifdef NOTYET
 231         RuleStmt   *replace_rule;
 232         RuleStmt   *append_rule;
 233         RuleStmt   *delete_rule;
 234 #endif
 235
 236         retrieve_rule = FormViewRetrieveRule(view, viewParse, replace);
 237
 238 #ifdef NOTYET
 239         replace_rule = FormViewReplaceRule(view, viewParse);
 240         append_rule = FormViewAppendRule(view, viewParse);
 241         delete_rule = FormViewDeleteRule(view, viewParse);
 242 #endif
 243
 244         DefineQueryRewrite(retrieve_rule);
 245
 246 #ifdef NOTYET
 247         DefineQueryRewrite(replace_rule);
 248         DefineQueryRewrite(append_rule);
 249         DefineQueryRewrite(delete_rule);
 250 #endif
 251
 252 }
 253
 254 /*---------------------------------------------------------------
 255  * UpdateRangeTableOfViewParse
 256  *
 257  * Update the range table of the given parsetree.
 258  * This update consists of adding two new entries IN THE BEGINNING
 259  * of the range table (otherwise the rule system will die a slow,
 260  * horrible and painful death, and we do not want that now, do we?)
 261  * one for the OLD relation and one for the NEW one (both of
 262  * them refer in fact to the "view" relation).
 263  *
 264  * Of course we must also increase the 'varnos' of all the Var nodes
 265  * by 2...
 266  *
 267  * These extra RT entries are not actually used in the query,
 268  * except for run-time permission checking.
 269  *---------------------------------------------------------------
 270  */
 271 static Query *
 272 UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
 273 {
 274         List       *new_rt;
 275         RangeTblEntry *rt_entry1,
 276                            *rt_entry2;
 277
 278         /*
 279          * Make a copy of the given parsetree.  It's not so much that we don't
 280          * want to scribble on our input, it's that the parser has a bad habit
 281          * of outputting multiple links to the same subtree for constructs
 282          * like BETWEEN, and we mustn't have OffsetVarNodes increment the
 283          * varno of a Var node twice.  copyObject will expand any
 284          * multiply-referenced subtree into multiple copies.
 285          */
 286         viewParse = (Query *) copyObject(viewParse);
 287
 288         /*
 289          * Create the 2 new range table entries and form the new range
 290          * table... OLD first, then NEW....
 291          */
 292         rt_entry1 = addRangeTableEntryForRelation(NULL, viewOid,
 293                                                                                           makeAlias("*OLD*", NIL),
 294                                                                                           false, false);
 295         rt_entry2 = addRangeTableEntryForRelation(NULL, viewOid,
 296                                                                                           makeAlias("*NEW*", NIL),
 297                                                                                           false, false);
 298         /* Must override addRangeTableEntry's default access-check flags */
 299         rt_entry1->checkForRead = false;
 300         rt_entry2->checkForRead = false;
 301
 302         new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));
 303
 304         viewParse->rtable = new_rt;
 305
 306         /*
 307          * Now offset all var nodes by 2, and jointree RT indexes too.
 308          */
 309         OffsetVarNodes((Node *) viewParse, 2, 0);
 310
 311         return viewParse;
 312 }
 313
 314 /*-------------------------------------------------------------------
 315  * DefineView
 316  *
 317  *              - takes a "viewname", "parsetree" pair and then
 318  *              1)              construct the "virtual" relation
 319  *              2)              commit the command but NOT the transaction,
 320  *                              so that the relation exists
 321  *                              before the rules are defined.
 322  *              2)              define the "n" rules specified in the PRS2 paper
 323  *                              over the "virtual" relation
 324  *-------------------------------------------------------------------
 325  */
 326 void
 327 DefineView(const RangeVar *view, Query *viewParse, bool replace)
 328 {
 329         Oid                     viewOid;
 330
 331         /*
 332          * Create the view relation
 333          *
 334          * NOTE: if it already exists and replace is false, the xact will be
 335          * aborted.
 336          */
 337
 338         viewOid = DefineVirtualRelation(view, viewParse->targetList, replace);
 339
 340         /*
 341          * The relation we have just created is not visible to any other
 342          * commands running with the same transaction & command id. So,
 343          * increment the command id counter (but do NOT pfree any memory!!!!)
 344          */
 345         CommandCounterIncrement();
 346
 347         /*
 348          * The range table of 'viewParse' does not contain entries for the
 349          * "OLD" and "NEW" relations. So... add them!
 350          */
 351         viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);
 352
 353         /*
 354          * Now create the rules associated with the view.
 355          */
 356         DefineViewRules(view, viewParse, replace);
 357 }
 358
 359 /*
 360  * RemoveView
 361  *
 362  * Remove a view given its name
 363  *
 364  * We just have to drop the relation; the associated rules will be
 365  * cleaned up automatically.
 366  */
 367 void
 368 RemoveView(const RangeVar *view, DropBehavior behavior)
 369 {
 370         Oid                     viewOid;
 371         ObjectAddress object;
 372
 373         viewOid = RangeVarGetRelid(view, false);
 374
 375         object.classId = RelOid_pg_class;
 376         object.objectId = viewOid;
 377         object.objectSubId = 0;
 378
 379         performDeletion(&object, behavior);
 380 }