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 1.72 2002/09/22 19:42:50 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                 elog(ERROR, "attempted to define virtual relation with no attrs");
  88
  89         /*
  90          * Check to see if we want to replace an existing view.
  91          */
  92         namespaceId = RangeVarGetCreationNamespace(relation);
  93         viewOid = get_relname_relid(relation->relname, namespaceId);
  94
  95         if (OidIsValid(viewOid) && replace)
  96         {
  97                 Relation        rel;
  98                 TupleDesc       descriptor;
  99
 100                 /*
 101                  * Yes.  Get exclusive lock on the existing view ...
 102                  */
 103                 rel = relation_open(viewOid, AccessExclusiveLock);
 104
 105                 /*
 106                  * Make sure it *is* a view, and do permissions checks.
 107                  */
 108                 if (rel->rd_rel->relkind != RELKIND_VIEW)
 109                         elog(ERROR, "%s is not a view",
 110                                  RelationGetRelationName(rel));
 111
 112                 if (!pg_class_ownercheck(viewOid, GetUserId()))
 113                         aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(rel));
 114
 115                 /*
 116                  * Create a tuple descriptor to compare against the existing view,
 117                  * and verify it matches.
 118                  */
 119                 descriptor = BuildDescForRelation(attrList);
 120                 checkViewTupleDesc(descriptor, rel->rd_att);
 121
 122                 /*
 123                  * Seems okay, so return the OID of the pre-existing view.
 124                  */
 125                 relation_close(rel, NoLock);    /* keep the lock! */
 126
 127                 return viewOid;
 128         }
 129         else
 130         {
 131                 /*
 132                  * now create the parameters for keys/inheritance etc. All of them
 133                  * are nil...
 134                  */
 135                 createStmt->relation = (RangeVar *) relation;
 136                 createStmt->tableElts = attrList;
 137                 createStmt->inhRelations = NIL;
 138                 createStmt->constraints = NIL;
 139                 createStmt->hasoids = false;
 140
 141                 /*
 142                  * finally create the relation (this will error out if there's an
 143                  * existing view, so we don't need more code to complain if
 144                  * "replace" is false).
 145                  */
 146                 return DefineRelation(createStmt, RELKIND_VIEW);
 147         }
 148 }
 149
 150 /*
 151  * Verify that tupledesc associated with proposed new view definition
 152  * matches tupledesc of old view.  This is basically a cut-down version
 153  * of equalTupleDescs(), with code added to generate specific complaints.
 154  */
 155 static void
 156 checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
 157 {
 158         int                     i;
 159
 160         if (newdesc->natts != olddesc->natts)
 161                 elog(ERROR, "Cannot change number of columns in view");
 162         /* we can ignore tdhasoid */
 163
 164         for (i = 0; i < newdesc->natts; i++)
 165         {
 166                 Form_pg_attribute newattr = newdesc->attrs[i];
 167                 Form_pg_attribute oldattr = olddesc->attrs[i];
 168
 169                 /* XXX not right, but we don't support DROP COL on view anyway */
 170                 if (newattr->attisdropped != oldattr->attisdropped)
 171                         elog(ERROR, "Cannot change number of columns in view");
 172
 173                 if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
 174                         elog(ERROR, "Cannot change name of view column \"%s\"",
 175                                  NameStr(oldattr->attname));
 176                 /* XXX would it be safe to allow atttypmod to change?  Not sure */
 177                 if (newattr->atttypid != oldattr->atttypid ||
 178                         newattr->atttypmod != oldattr->atttypmod)
 179                         elog(ERROR, "Cannot change datatype of view column \"%s\"",
 180                                  NameStr(oldattr->attname));
 181                 /* We can ignore the remaining attributes of an attribute... */
 182         }
 183
 184         /*
 185          * We ignore the constraint fields.  The new view desc can't have any
 186          * constraints, and the only ones that could be on the old view are
 187          * defaults, which we are happy to leave in place.
 188          */
 189 }
 190
 191 static RuleStmt *
 192 FormViewRetrieveRule(const RangeVar *view, Query *viewParse, bool replace)
 193 {
 194         RuleStmt   *rule;
 195
 196         /*
 197          * Create a RuleStmt that corresponds to the suitable rewrite rule
 198          * args for DefineQueryRewrite();
 199          */
 200         rule = makeNode(RuleStmt);
 201         rule->relation = copyObject((RangeVar *) view);
 202         rule->rulename = pstrdup(ViewSelectRuleName);
 203         rule->whereClause = NULL;
 204         rule->event = CMD_SELECT;
 205         rule->instead = true;
 206         rule->actions = makeList1(viewParse);
 207         rule->replace = replace;
 208
 209         return rule;
 210 }
 211
 212 static void
 213 DefineViewRules(const RangeVar *view, Query *viewParse, bool replace)
 214 {
 215         RuleStmt   *retrieve_rule;
 216
 217 #ifdef NOTYET
 218         RuleStmt   *replace_rule;
 219         RuleStmt   *append_rule;
 220         RuleStmt   *delete_rule;
 221 #endif
 222
 223         retrieve_rule = FormViewRetrieveRule(view, viewParse, replace);
 224
 225 #ifdef NOTYET
 226         replace_rule = FormViewReplaceRule(view, viewParse);
 227         append_rule = FormViewAppendRule(view, viewParse);
 228         delete_rule = FormViewDeleteRule(view, viewParse);
 229 #endif
 230
 231         DefineQueryRewrite(retrieve_rule);
 232
 233 #ifdef NOTYET
 234         DefineQueryRewrite(replace_rule);
 235         DefineQueryRewrite(append_rule);
 236         DefineQueryRewrite(delete_rule);
 237 #endif
 238
 239 }
 240
 241 /*---------------------------------------------------------------
 242  * UpdateRangeTableOfViewParse
 243  *
 244  * Update the range table of the given parsetree.
 245  * This update consists of adding two new entries IN THE BEGINNING
 246  * of the range table (otherwise the rule system will die a slow,
 247  * horrible and painful death, and we do not want that now, do we?)
 248  * one for the OLD relation and one for the NEW one (both of
 249  * them refer in fact to the "view" relation).
 250  *
 251  * Of course we must also increase the 'varnos' of all the Var nodes
 252  * by 2...
 253  *
 254  * These extra RT entries are not actually used in the query,
 255  * except for run-time permission checking.
 256  *---------------------------------------------------------------
 257  */
 258 static Query *
 259 UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
 260 {
 261         List       *new_rt;
 262         RangeTblEntry *rt_entry1,
 263                            *rt_entry2;
 264
 265         /*
 266          * Make a copy of the given parsetree.  It's not so much that we don't
 267          * want to scribble on our input, it's that the parser has a bad habit
 268          * of outputting multiple links to the same subtree for constructs
 269          * like BETWEEN, and we mustn't have OffsetVarNodes increment the
 270          * varno of a Var node twice.  copyObject will expand any
 271          * multiply-referenced subtree into multiple copies.
 272          */
 273         viewParse = (Query *) copyObject(viewParse);
 274
 275         /*
 276          * Create the 2 new range table entries and form the new range
 277          * table... OLD first, then NEW....
 278          */
 279         rt_entry1 = addRangeTableEntryForRelation(NULL, viewOid,
 280                                                                                           makeAlias("*OLD*", NIL),
 281                                                                                           false, false);
 282         rt_entry2 = addRangeTableEntryForRelation(NULL, viewOid,
 283                                                                                           makeAlias("*NEW*", NIL),
 284                                                                                           false, false);
 285         /* Must override addRangeTableEntry's default access-check flags */
 286         rt_entry1->checkForRead = false;
 287         rt_entry2->checkForRead = false;
 288
 289         new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));
 290
 291         viewParse->rtable = new_rt;
 292
 293         /*
 294          * Now offset all var nodes by 2, and jointree RT indexes too.
 295          */
 296         OffsetVarNodes((Node *) viewParse, 2, 0);
 297
 298         return viewParse;
 299 }
 300
 301 /*-------------------------------------------------------------------
 302  * DefineView
 303  *
 304  *              - takes a "viewname", "parsetree" pair and then
 305  *              1)              construct the "virtual" relation
 306  *              2)              commit the command but NOT the transaction,
 307  *                              so that the relation exists
 308  *                              before the rules are defined.
 309  *              2)              define the "n" rules specified in the PRS2 paper
 310  *                              over the "virtual" relation
 311  *-------------------------------------------------------------------
 312  */
 313 void
 314 DefineView(const RangeVar *view, Query *viewParse, bool replace)
 315 {
 316         Oid                     viewOid;
 317
 318         /*
 319          * Create the view relation
 320          *
 321          * NOTE: if it already exists and replace is false, the xact will be
 322          * aborted.
 323          */
 324
 325         viewOid = DefineVirtualRelation(view, viewParse->targetList, replace);
 326
 327         /*
 328          * The relation we have just created is not visible to any other
 329          * commands running with the same transaction & command id. So,
 330          * increment the command id counter (but do NOT pfree any memory!!!!)
 331          */
 332         CommandCounterIncrement();
 333
 334         /*
 335          * The range table of 'viewParse' does not contain entries for the
 336          * "OLD" and "NEW" relations. So... add them!
 337          */
 338         viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);
 339
 340         /*
 341          * Now create the rules associated with the view.
 342          */
 343         DefineViewRules(view, viewParse, replace);
 344 }
 345
 346 /*
 347  * RemoveView
 348  *
 349  * Remove a view given its name
 350  *
 351  * We just have to drop the relation; the associated rules will be
 352  * cleaned up automatically.
 353  */
 354 void
 355 RemoveView(const RangeVar *view, DropBehavior behavior)
 356 {
 357         Oid                     viewOid;
 358         ObjectAddress object;
 359
 360         viewOid = RangeVarGetRelid(view, false);
 361
 362         object.classId = RelOid_pg_class;
 363         object.objectId = viewOid;
 364         object.objectSubId = 0;
 365
 366         performDeletion(&object, behavior);
 367 }