src/fkey.c

   1 /*
   2 **
   3 ** The author disclaims copyright to this source code.  In place of
   4 ** a legal notice, here is a blessing:
   5 **
   6 **    May you do good and not evil.
   7 **    May you find forgiveness for yourself and forgive others.
   8 **    May you share freely, never taking more than you give.
   9 **
  10 *************************************************************************
  11 ** This file contains code used by the compiler to add foreign key
  12 ** support to compiled SQL statements.
  13 */
  14 #include "sqliteInt.h"
  15
  16 #ifndef SQLITE_OMIT_FOREIGN_KEY
  17 #ifndef SQLITE_OMIT_TRIGGER
  18
  19 /*
  20 ** Deferred and Immediate FKs
  21 ** --------------------------
  22 **
  23 ** Foreign keys in SQLite come in two flavours: deferred and immediate.
  24 ** If an immediate foreign key constraint is violated,
  25 ** SQLITE_CONSTRAINT_FOREIGNKEY is returned and the current
  26 ** statement transaction rolled back. If a
  27 ** deferred foreign key constraint is violated, no action is taken
  28 ** immediately. However if the application attempts to commit the
  29 ** transaction before fixing the constraint violation, the attempt fails.
  30 **
  31 ** Deferred constraints are implemented using a simple counter associated
  32 ** with the database handle. The counter is set to zero each time a
  33 ** database transaction is opened. Each time a statement is executed
  34 ** that causes a foreign key violation, the counter is incremented. Each
  35 ** time a statement is executed that removes an existing violation from
  36 ** the database, the counter is decremented. When the transaction is
  37 ** committed, the commit fails if the current value of the counter is
  38 ** greater than zero. This scheme has two big drawbacks:
  39 **
  40 **   * When a commit fails due to a deferred foreign key constraint,
  41 **     there is no way to tell which foreign constraint is not satisfied,
  42 **     or which row it is not satisfied for.
  43 **
  44 **   * If the database contains foreign key violations when the
  45 **     transaction is opened, this may cause the mechanism to malfunction.
  46 **
  47 ** Despite these problems, this approach is adopted as it seems simpler
  48 ** than the alternatives.
  49 **
  50 ** INSERT operations:
  51 **
  52 **   I.1) For each FK for which the table is the child table, search
  53 **        the parent table for a match. If none is found increment the
  54 **        constraint counter.
  55 **
  56 **   I.2) For each FK for which the table is the parent table,
  57 **        search the child table for rows that correspond to the new
  58 **        row in the parent table. Decrement the counter for each row
  59 **        found (as the constraint is now satisfied).
  60 **
  61 ** DELETE operations:
  62 **
  63 **   D.1) For each FK for which the table is the child table,
  64 **        search the parent table for a row that corresponds to the
  65 **        deleted row in the child table. If such a row is not found,
  66 **        decrement the counter.
  67 **
  68 **   D.2) For each FK for which the table is the parent table, search
  69 **        the child table for rows that correspond to the deleted row
  70 **        in the parent table. For each found increment the counter.
  71 **
  72 ** UPDATE operations:
  73 **
  74 **   An UPDATE command requires that all 4 steps above are taken, but only
  75 **   for FK constraints for which the affected columns are actually
  76 **   modified (values must be compared at runtime).
  77 **
  78 ** Note that I.1 and D.1 are very similar operations, as are I.2 and D.2.
  79 ** This simplifies the implementation a bit.
  80 **
  81 ** For the purposes of immediate FK constraints, the OR REPLACE conflict
  82 ** resolution is considered to delete rows before the new row is inserted.
  83 ** If a delete caused by OR REPLACE violates an FK constraint, an exception
  84 ** is thrown, even if the FK constraint would be satisfied after the new
  85 ** row is inserted.
  86 **
  87 ** Immediate constraints are usually handled similarly. The only difference
  88 ** is that the counter used is stored as part of each individual statement
  89 ** object (struct Vdbe). If, after the statement has run, its immediate
  90 ** constraint counter is greater than zero,
  91 ** it returns SQLITE_CONSTRAINT_FOREIGNKEY
  92 ** and the statement transaction is rolled back. An exception is an INSERT
  93 ** statement that inserts a single row only (no triggers). In this case,
  94 ** instead of using a counter, an exception is thrown immediately if the
  95 ** INSERT violates a foreign key constraint. This is necessary as such
  96 ** an INSERT does not open a statement transaction.
  97 **
  98 ** TODO: How should dropping a table be handled? How should renaming a
  99 ** table be handled?
 100 **
 101 **
 102 ** Query API Notes
 103 ** ---------------
 104 **
 105 ** Before coding an UPDATE or DELETE row operation, the code-generator
 106 ** for those two operations needs to know whether or not the operation
 107 ** requires any FK processing and, if so, which columns of the original
 108 ** row are required by the FK processing VDBE code (i.e. if FKs were
 109 ** implemented using triggers, which of the old.* columns would be
 110 ** accessed). No information is required by the code-generator before
 111 ** coding an INSERT operation. The functions used by the UPDATE/DELETE
 112 ** generation code to query for this information are:
 113 **
 114 **   sqlite3FkRequired() - Test to see if FK processing is required.
 115 **   sqlite3FkOldmask()  - Query for the set of required old.* columns.
 116 **
 117 **
 118 ** Externally accessible module functions
 119 ** --------------------------------------
 120 **
 121 **   sqlite3FkCheck()    - Check for foreign key violations.
 122 **   sqlite3FkActions()  - Code triggers for ON UPDATE/ON DELETE actions.
 123 **   sqlite3FkDelete()   - Delete an FKey structure.
 124 */
 125
 126 /*
 127 ** VDBE Calling Convention
 128 ** -----------------------
 129 **
 130 ** Example:
 131 **
 132 **   For the following INSERT statement:
 133 **
 134 **     CREATE TABLE t1(a, b INTEGER PRIMARY KEY, c);
 135 **     INSERT INTO t1 VALUES(1, 2, 3.1);
 136 **
 137 **   Register (x):        2    (type integer)
 138 **   Register (x+1):      1    (type integer)
 139 **   Register (x+2):      NULL (type NULL)
 140 **   Register (x+3):      3.1  (type real)
 141 */
 142
 143 /*
 144 ** A foreign key constraint requires that the key columns in the parent
 145 ** table are collectively subject to a UNIQUE or PRIMARY KEY constraint.
 146 ** Given that pParent is the parent table for foreign key constraint pFKey,
 147 ** search the schema for a unique index on the parent key columns.
 148 **
 149 ** If successful, zero is returned. If the parent key is an INTEGER PRIMARY
 150 ** KEY column, then output variable *ppIdx is set to NULL. Otherwise, *ppIdx
 151 ** is set to point to the unique index.
 152 **
 153 ** If the parent key consists of a single column (the foreign key constraint
 154 ** is not a composite foreign key), output variable *paiCol is set to NULL.
 155 ** Otherwise, it is set to point to an allocated array of size N, where
 156 ** N is the number of columns in the parent key. The first element of the
 157 ** array is the index of the child table column that is mapped by the FK
 158 ** constraint to the parent table column stored in the left-most column
 159 ** of index *ppIdx. The second element of the array is the index of the
 160 ** child table column that corresponds to the second left-most column of
 161 ** *ppIdx, and so on.
 162 **
 163 ** If the required index cannot be found, either because:
 164 **
 165 **   1) The named parent key columns do not exist, or
 166 **
 167 **   2) The named parent key columns do exist, but are not subject to a
 168 **      UNIQUE or PRIMARY KEY constraint, or
 169 **
 170 **   3) No parent key columns were provided explicitly as part of the
 171 **      foreign key definition, and the parent table does not have a
 172 **      PRIMARY KEY, or
 173 **
 174 **   4) No parent key columns were provided explicitly as part of the
 175 **      foreign key definition, and the PRIMARY KEY of the parent table
 176 **      consists of a different number of columns to the child key in
 177 **      the child table.
 178 **
 179 ** then non-zero is returned, and a "foreign key mismatch" error loaded
 180 ** into pParse. If an OOM error occurs, non-zero is returned and the
 181 ** pParse->db->mallocFailed flag is set.
 182 */
 183 int sqlite3FkLocateIndex(
 184   Parse *pParse,                  /* Parse context to store any error in */
 185   Table *pParent,                 /* Parent table of FK constraint pFKey */
 186   FKey *pFKey,                    /* Foreign key to find index for */
 187   Index **ppIdx,                  /* OUT: Unique index on parent table */
 188   int **paiCol                    /* OUT: Map of index columns in pFKey */
 189 ){
 190   Index *pIdx = 0;                    /* Value to return via *ppIdx */
 191   int *aiCol = 0;                     /* Value to return via *paiCol */
 192   int nCol = pFKey->nCol;             /* Number of columns in parent key */
 193   char *zKey = pFKey->aCol[0].zCol;   /* Name of left-most parent key column */
 194
 195   /* The caller is responsible for zeroing output parameters. */
 196   assert( ppIdx && *ppIdx==0 );
 197   assert( !paiCol || *paiCol==0 );
 198   assert( pParse );
 199
 200   /* If this is a non-composite (single column) foreign key, check if it
 201   ** maps to the INTEGER PRIMARY KEY of table pParent. If so, leave *ppIdx
 202   ** and *paiCol set to zero and return early.
 203   **
 204   ** Otherwise, for a composite foreign key (more than one column), allocate
 205   ** space for the aiCol array (returned via output parameter *paiCol).
 206   ** Non-composite foreign keys do not require the aiCol array.
 207   */
 208   if( nCol==1 ){
 209     /* The FK maps to the IPK if any of the following are true:
 210     **
 211     **   1) There is an INTEGER PRIMARY KEY column and the FK is implicitly
 212     **      mapped to the primary key of table pParent, or
 213     **   2) The FK is explicitly mapped to a column declared as INTEGER
 214     **      PRIMARY KEY.
 215     */
 216     if( pParent->iPKey>=0 ){
 217       if( !zKey ) return 0;
 218       if( !sqlite3StrICmp(pParent->aCol[pParent->iPKey].zName, zKey) ) return 0;
 219     }
 220   }else if( paiCol ){
 221     assert( nCol>1 );
 222     aiCol = (int *)sqlite3DbMallocRawNN(pParse->db, nCol*sizeof(int));
 223     if( !aiCol ) return 1;
 224     *paiCol = aiCol;
 225   }
 226
 227   for(pIdx=pParent->pIndex; pIdx; pIdx=pIdx->pNext){
 228     if( pIdx->nKeyCol==nCol && IsUniqueIndex(pIdx) && pIdx->pPartIdxWhere==0 ){
 229       /* pIdx is a UNIQUE index (or a PRIMARY KEY) and has the right number
 230       ** of columns. If each indexed column corresponds to a foreign key
 231       ** column of pFKey, then this index is a winner.  */
 232
 233       if( zKey==0 ){
 234         /* If zKey is NULL, then this foreign key is implicitly mapped to
 235         ** the PRIMARY KEY of table pParent. The PRIMARY KEY index may be
 236         ** identified by the test.  */
 237         if( IsPrimaryKeyIndex(pIdx) ){
 238           if( aiCol ){
 239             int i;
 240             for(i=0; i<nCol; i++) aiCol[i] = pFKey->aCol[i].iFrom;
 241           }
 242           break;
 243         }
 244       }else{
 245         /* If zKey is non-NULL, then this foreign key was declared to
 246         ** map to an explicit list of columns in table pParent. Check if this
 247         ** index matches those columns. Also, check that the index uses
 248         ** the default collation sequences for each column. */
 249         int i, j;
 250         for(i=0; i<nCol; i++){
 251           i16 iCol = pIdx->aiColumn[i];     /* Index of column in parent tbl */
 252           const char *zDfltColl;            /* Def. collation for column */
 253           char *zIdxCol;                    /* Name of indexed column */
 254
 255           if( iCol<0 ) break; /* No foreign keys against expression indexes */
 256
 257           /* If the index uses a collation sequence that is different from
 258           ** the default collation sequence for the column, this index is
 259           ** unusable. Bail out early in this case.  */
 260           zDfltColl = pParent->aCol[iCol].zColl;
 261           if( !zDfltColl ) zDfltColl = sqlite3StrBINARY;
 262           if( sqlite3StrICmp(pIdx->azColl[i], zDfltColl) ) break;
 263
 264           zIdxCol = pParent->aCol[iCol].zName;
 265           for(j=0; j<nCol; j++){
 266             if( sqlite3StrICmp(pFKey->aCol[j].zCol, zIdxCol)==0 ){
 267               if( aiCol ) aiCol[i] = pFKey->aCol[j].iFrom;
 268               break;
 269             }
 270           }
 271           if( j==nCol ) break;
 272         }
 273         if( i==nCol ) break;      /* pIdx is usable */
 274       }
 275     }
 276   }
 277
 278   if( !pIdx ){
 279     if( !pParse->disableTriggers ){
 280       sqlite3ErrorMsg(pParse,
 281            "foreign key mismatch - \"%w\" referencing \"%w\"",
 282            pFKey->pFrom->zName, pFKey->zTo);
 283     }
 284     sqlite3DbFree(pParse->db, aiCol);
 285     return 1;
 286   }
 287
 288   *ppIdx = pIdx;
 289   return 0;
 290 }
 291
 292 /*
 293 ** This function is called when a row is inserted into or deleted from the
 294 ** child table of foreign key constraint pFKey. If an SQL UPDATE is executed
 295 ** on the child table of pFKey, this function is invoked twice for each row
 296 ** affected - once to "delete" the old row, and then again to "insert" the
 297 ** new row.
 298 **
 299 ** Each time it is called, this function generates VDBE code to locate the
 300 ** row in the parent table that corresponds to the row being inserted into
 301 ** or deleted from the child table. If the parent row can be found, no
 302 ** special action is taken. Otherwise, if the parent row can *not* be
 303 ** found in the parent table:
 304 **
 305 **   Operation | FK type   | Action taken
 306 **   --------------------------------------------------------------------------
 307 **   INSERT      immediate   Increment the "immediate constraint counter".
 308 **
 309 **   DELETE      immediate   Decrement the "immediate constraint counter".
 310 **
 311 **   INSERT      deferred    Increment the "deferred constraint counter".
 312 **
 313 **   DELETE      deferred    Decrement the "deferred constraint counter".
 314 **
 315 ** These operations are identified in the comment at the top of this file
 316 ** (fkey.c) as "I.1" and "D.1".
 317 */
 318 static void fkLookupParent(
 319   Parse *pParse,        /* Parse context */
 320   int iDb,              /* Index of database housing pTab */
 321   Table *pTab,          /* Parent table of FK pFKey */
 322   Index *pIdx,          /* Unique index on parent key columns in pTab */
 323   FKey *pFKey,          /* Foreign key constraint */
 324   int *aiCol,           /* Map from parent key columns to child table columns */
 325   int regData,          /* Address of array containing child table row */
 326   int nIncr,            /* Increment constraint counter by this */
 327   int isIgnore          /* If true, pretend pTab contains all NULL values */
 328 ){
 329   int i;                                    /* Iterator variable */
 330   Vdbe *v = sqlite3GetVdbe(pParse);         /* Vdbe to add code to */
 331   int iCur = pParse->nTab - 1;              /* Cursor number to use */
 332   int iOk = sqlite3VdbeMakeLabel(v);        /* jump here if parent key found */
 333
 334   /* If nIncr is less than zero, then check at runtime if there are any
 335   ** outstanding constraints to resolve. If there are not, there is no need
 336   ** to check if deleting this row resolves any outstanding violations.
 337   **
 338   ** Check if any of the key columns in the child table row are NULL. If
 339   ** any are, then the constraint is considered satisfied. No need to
 340   ** search for a matching row in the parent table.  */
 341   if( nIncr<0 ){
 342     sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, iOk);
 343     VdbeCoverage(v);
 344   }
 345   for(i=0; i<pFKey->nCol; i++){
 346     int iReg = aiCol[i] + regData + 1;
 347     sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iOk); VdbeCoverage(v);
 348   }
 349
 350   if( isIgnore==0 ){
 351     if( pIdx==0 ){
 352       /* If pIdx is NULL, then the parent key is the INTEGER PRIMARY KEY
 353       ** column of the parent table (table pTab).  */
 354       int iMustBeInt;               /* Address of MustBeInt instruction */
 355       int regTemp = sqlite3GetTempReg(pParse);
 356
 357       /* Invoke MustBeInt to coerce the child key value to an integer (i.e.
 358       ** apply the affinity of the parent key). If this fails, then there
 359       ** is no matching parent key. Before using MustBeInt, make a copy of
 360       ** the value. Otherwise, the value inserted into the child key column
 361       ** will have INTEGER affinity applied to it, which may not be correct.  */
 362       sqlite3VdbeAddOp2(v, OP_SCopy, aiCol[0]+1+regData, regTemp);
 363       iMustBeInt = sqlite3VdbeAddOp2(v, OP_MustBeInt, regTemp, 0);
 364       VdbeCoverage(v);
 365
 366       /* If the parent table is the same as the child table, and we are about
 367       ** to increment the constraint-counter (i.e. this is an INSERT operation),
 368       ** then check if the row being inserted matches itself. If so, do not
 369       ** increment the constraint-counter.  */
 370       if( pTab==pFKey->pFrom && nIncr==1 ){
 371         sqlite3VdbeAddOp3(v, OP_Eq, regData, iOk, regTemp); VdbeCoverage(v);
 372         sqlite3VdbeChangeP5(v, SQLITE_NOTNULL);
 373       }
 374
 375       sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);
 376       sqlite3VdbeAddOp3(v, OP_NotExists, iCur, 0, regTemp); VdbeCoverage(v);
 377       sqlite3VdbeGoto(v, iOk);
 378       sqlite3VdbeJumpHere(v, sqlite3VdbeCurrentAddr(v)-2);
 379       sqlite3VdbeJumpHere(v, iMustBeInt);
 380       sqlite3ReleaseTempReg(pParse, regTemp);
 381     }else{
 382       int nCol = pFKey->nCol;
 383       int regTemp = sqlite3GetTempRange(pParse, nCol);
 384       int regRec = sqlite3GetTempReg(pParse);
 385
 386       sqlite3VdbeAddOp3(v, OP_OpenRead, iCur, pIdx->tnum, iDb);
 387       sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
 388       for(i=0; i<nCol; i++){
 389         sqlite3VdbeAddOp2(v, OP_Copy, aiCol[i]+1+regData, regTemp+i);
 390       }
 391
 392       /* If the parent table is the same as the child table, and we are about
 393       ** to increment the constraint-counter (i.e. this is an INSERT operation),
 394       ** then check if the row being inserted matches itself. If so, do not
 395       ** increment the constraint-counter.
 396       **
 397       ** If any of the parent-key values are NULL, then the row cannot match
 398       ** itself. So set JUMPIFNULL to make sure we do the OP_Found if any
 399       ** of the parent-key values are NULL (at this point it is known that
 400       ** none of the child key values are).
 401       */
 402       if( pTab==pFKey->pFrom && nIncr==1 ){
 403         int iJump = sqlite3VdbeCurrentAddr(v) + nCol + 1;
 404         for(i=0; i<nCol; i++){
 405           int iChild = aiCol[i]+1+regData;
 406           int iParent = pIdx->aiColumn[i]+1+regData;
 407           assert( pIdx->aiColumn[i]>=0 );
 408           assert( aiCol[i]!=pTab->iPKey );
 409           if( pIdx->aiColumn[i]==pTab->iPKey ){
 410             /* The parent key is a composite key that includes the IPK column */
 411             iParent = regData;
 412           }
 413           sqlite3VdbeAddOp3(v, OP_Ne, iChild, iJump, iParent); VdbeCoverage(v);
 414           sqlite3VdbeChangeP5(v, SQLITE_JUMPIFNULL);
 415         }
 416         sqlite3VdbeGoto(v, iOk);
 417       }
 418
 419       sqlite3VdbeAddOp4(v, OP_MakeRecord, regTemp, nCol, regRec,
 420                         sqlite3IndexAffinityStr(pParse->db,pIdx), nCol);
 421       sqlite3VdbeAddOp4Int(v, OP_Found, iCur, iOk, regRec, 0); VdbeCoverage(v);
 422
 423       sqlite3ReleaseTempReg(pParse, regRec);
 424       sqlite3ReleaseTempRange(pParse, regTemp, nCol);
 425     }
 426   }
 427
 428   if( !pFKey->isDeferred && !(pParse->db->flags & SQLITE_DeferFKs)
 429    && !pParse->pToplevel
 430    && !pParse->isMultiWrite
 431   ){
 432     /* Special case: If this is an INSERT statement that will insert exactly
 433     ** one row into the table, raise a constraint immediately instead of
 434     ** incrementing a counter. This is necessary as the VM code is being
 435     ** generated for will not open a statement transaction.  */
 436     assert( nIncr==1 );
 437     sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
 438         OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
 439   }else{
 440     if( nIncr>0 && pFKey->isDeferred==0 ){
 441       sqlite3MayAbort(pParse);
 442     }
 443     sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
 444   }
 445
 446   sqlite3VdbeResolveLabel(v, iOk);
 447   sqlite3VdbeAddOp1(v, OP_Close, iCur);
 448 }
 449
 450
 451 /*
 452 ** Return an Expr object that refers to a memory register corresponding
 453 ** to column iCol of table pTab.
 454 **
 455 ** regBase is the first of an array of register that contains the data
 456 ** for pTab.  regBase itself holds the rowid.  regBase+1 holds the first
 457 ** column.  regBase+2 holds the second column, and so forth.
 458 */
 459 static Expr *exprTableRegister(
 460   Parse *pParse,     /* Parsing and code generating context */
 461   Table *pTab,       /* The table whose content is at r[regBase]... */
 462   int regBase,       /* Contents of table pTab */
 463   i16 iCol           /* Which column of pTab is desired */
 464 ){
 465   Expr *pExpr;
 466   Column *pCol;
 467   const char *zColl;
 468   sqlite3 *db = pParse->db;
 469
 470   pExpr = sqlite3Expr(db, TK_REGISTER, 0);
 471   if( pExpr ){
 472     if( iCol>=0 && iCol!=pTab->iPKey ){
 473       pCol = &pTab->aCol[iCol];
 474       pExpr->iTable = regBase + iCol + 1;
 475       pExpr->affinity = pCol->affinity;
 476       zColl = pCol->zColl;
 477       if( zColl==0 ) zColl = db->pDfltColl->zName;
 478       pExpr = sqlite3ExprAddCollateString(pParse, pExpr, zColl);
 479     }else{
 480       pExpr->iTable = regBase;
 481       pExpr->affinity = SQLITE_AFF_INTEGER;
 482     }
 483   }
 484   return pExpr;
 485 }
 486
 487 /*
 488 ** Return an Expr object that refers to column iCol of table pTab which
 489 ** has cursor iCur.
 490 */
 491 static Expr *exprTableColumn(
 492   sqlite3 *db,      /* The database connection */
 493   Table *pTab,      /* The table whose column is desired */
 494   int iCursor,      /* The open cursor on the table */
 495   i16 iCol          /* The column that is wanted */
 496 ){
 497   Expr *pExpr = sqlite3Expr(db, TK_COLUMN, 0);
 498   if( pExpr ){
 499     pExpr->pTab = pTab;
 500     pExpr->iTable = iCursor;
 501     pExpr->iColumn = iCol;
 502   }
 503   return pExpr;
 504 }
 505
 506 /*
 507 ** This function is called to generate code executed when a row is deleted
 508 ** from the parent table of foreign key constraint pFKey and, if pFKey is
 509 ** deferred, when a row is inserted into the same table. When generating
 510 ** code for an SQL UPDATE operation, this function may be called twice -
 511 ** once to "delete" the old row and once to "insert" the new row.
 512 **
 513 ** Parameter nIncr is passed -1 when inserting a row (as this may decrease
 514 ** the number of FK violations in the db) or +1 when deleting one (as this
 515 ** may increase the number of FK constraint problems).
 516 **
 517 ** The code generated by this function scans through the rows in the child
 518 ** table that correspond to the parent table row being deleted or inserted.
 519 ** For each child row found, one of the following actions is taken:
 520 **
 521 **   Operation | FK type   | Action taken
 522 **   --------------------------------------------------------------------------
 523 **   DELETE      immediate   Increment the "immediate constraint counter".
 524 **                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
 525 **                           throw a "FOREIGN KEY constraint failed" exception.
 526 **
 527 **   INSERT      immediate   Decrement the "immediate constraint counter".
 528 **
 529 **   DELETE      deferred    Increment the "deferred constraint counter".
 530 **                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
 531 **                           throw a "FOREIGN KEY constraint failed" exception.
 532 **
 533 **   INSERT      deferred    Decrement the "deferred constraint counter".
 534 **
 535 ** These operations are identified in the comment at the top of this file
 536 ** (fkey.c) as "I.2" and "D.2".
 537 */
 538 static void fkScanChildren(
 539   Parse *pParse,                  /* Parse context */
 540   SrcList *pSrc,                  /* The child table to be scanned */
 541   Table *pTab,                    /* The parent table */
 542   Index *pIdx,                    /* Index on parent covering the foreign key */
 543   FKey *pFKey,                    /* The foreign key linking pSrc to pTab */
 544   int *aiCol,                     /* Map from pIdx cols to child table cols */
 545   int regData,                    /* Parent row data starts here */
 546   int nIncr                       /* Amount to increment deferred counter by */
 547 ){
 548   sqlite3 *db = pParse->db;       /* Database handle */
 549   int i;                          /* Iterator variable */
 550   Expr *pWhere = 0;               /* WHERE clause to scan with */
 551   NameContext sNameContext;       /* Context used to resolve WHERE clause */
 552   WhereInfo *pWInfo;              /* Context used by sqlite3WhereXXX() */
 553   int iFkIfZero = 0;              /* Address of OP_FkIfZero */
 554   Vdbe *v = sqlite3GetVdbe(pParse);
 555
 556   assert( pIdx==0 || pIdx->pTable==pTab );
 557   assert( pIdx==0 || pIdx->nKeyCol==pFKey->nCol );
 558   assert( pIdx!=0 || pFKey->nCol==1 );
 559   assert( pIdx!=0 || HasRowid(pTab) );
 560
 561   if( nIncr<0 ){
 562     iFkIfZero = sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, 0);
 563     VdbeCoverage(v);
 564   }
 565
 566   /* Create an Expr object representing an SQL expression like:
 567   **
 568   **   <parent-key1> = <child-key1> AND <parent-key2> = <child-key2> ...
 569   **
 570   ** The collation sequence used for the comparison should be that of
 571   ** the parent key columns. The affinity of the parent key column should
 572   ** be applied to each child key value before the comparison takes place.
 573   */
 574   for(i=0; i<pFKey->nCol; i++){
 575     Expr *pLeft;                  /* Value from parent table row */
 576     Expr *pRight;                 /* Column ref to child table */
 577     Expr *pEq;                    /* Expression (pLeft = pRight) */
 578     i16 iCol;                     /* Index of column in child table */
 579     const char *zCol;             /* Name of column in child table */
 580
 581     iCol = pIdx ? pIdx->aiColumn[i] : -1;
 582     pLeft = exprTableRegister(pParse, pTab, regData, iCol);
 583     iCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
 584     assert( iCol>=0 );
 585     zCol = pFKey->pFrom->aCol[iCol].zName;
 586     pRight = sqlite3Expr(db, TK_ID, zCol);
 587     pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight);
 588     pWhere = sqlite3ExprAnd(db, pWhere, pEq);
 589   }
 590
 591   /* If the child table is the same as the parent table, then add terms
 592   ** to the WHERE clause that prevent this entry from being scanned.
 593   ** The added WHERE clause terms are like this:
 594   **
 595   **     $current_rowid!=rowid
 596   **     NOT( $current_a==a AND $current_b==b AND ... )
 597   **
 598   ** The first form is used for rowid tables.  The second form is used
 599   ** for WITHOUT ROWID tables.  In the second form, the primary key is
 600   ** (a,b,...)
 601   */
 602   if( pTab==pFKey->pFrom && nIncr>0 ){
 603     Expr *pNe;                    /* Expression (pLeft != pRight) */
 604     Expr *pLeft;                  /* Value from parent table row */
 605     Expr *pRight;                 /* Column ref to child table */
 606     if( HasRowid(pTab) ){
 607       pLeft = exprTableRegister(pParse, pTab, regData, -1);
 608       pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, -1);
 609       pNe = sqlite3PExpr(pParse, TK_NE, pLeft, pRight);
 610     }else{
 611       Expr *pEq, *pAll = 0;
 612       Index *pPk = sqlite3PrimaryKeyIndex(pTab);
 613       assert( pIdx!=0 );
 614       for(i=0; i<pPk->nKeyCol; i++){
 615         i16 iCol = pIdx->aiColumn[i];
 616         assert( iCol>=0 );
 617         pLeft = exprTableRegister(pParse, pTab, regData, iCol);
 618         pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, iCol);
 619         pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight);
 620         pAll = sqlite3ExprAnd(db, pAll, pEq);
 621       }
 622       pNe = sqlite3PExpr(pParse, TK_NOT, pAll, 0);
 623     }
 624     pWhere = sqlite3ExprAnd(db, pWhere, pNe);
 625   }
 626
 627   /* Resolve the references in the WHERE clause. */
 628   memset(&sNameContext, 0, sizeof(NameContext));
 629   sNameContext.pSrcList = pSrc;
 630   sNameContext.pParse = pParse;
 631   sqlite3ResolveExprNames(&sNameContext, pWhere);
 632
 633   /* Create VDBE to loop through the entries in pSrc that match the WHERE
 634   ** clause. For each row found, increment either the deferred or immediate
 635   ** foreign key constraint counter. */
 636   if( pParse->nErr==0 ){
 637     pWInfo = sqlite3WhereBegin(pParse, pSrc, pWhere, 0, 0, 0, 0);
 638     sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
 639     if( pWInfo ){
 640       sqlite3WhereEnd(pWInfo);
 641     }
 642   }
 643
 644   /* Clean up the WHERE clause constructed above. */
 645   sqlite3ExprDelete(db, pWhere);
 646   if( iFkIfZero ){
 647     sqlite3VdbeJumpHere(v, iFkIfZero);
 648   }
 649 }
 650
 651 /*
 652 ** This function returns a linked list of FKey objects (connected by
 653 ** FKey.pNextTo) holding all children of table pTab.  For example,
 654 ** given the following schema:
 655 **
 656 **   CREATE TABLE t1(a PRIMARY KEY);
 657 **   CREATE TABLE t2(b REFERENCES t1(a);
 658 **
 659 ** Calling this function with table "t1" as an argument returns a pointer
 660 ** to the FKey structure representing the foreign key constraint on table
 661 ** "t2". Calling this function with "t2" as the argument would return a
 662 ** NULL pointer (as there are no FK constraints for which t2 is the parent
 663 ** table).
 664 */
 665 FKey *sqlite3FkReferences(Table *pTab){
 666   return (FKey *)sqlite3HashFind(&pTab->pSchema->fkeyHash, pTab->zName);
 667 }
 668
 669 /*
 670 ** The second argument is a Trigger structure allocated by the
 671 ** fkActionTrigger() routine. This function deletes the Trigger structure
 672 ** and all of its sub-components.
 673 **
 674 ** The Trigger structure or any of its sub-components may be allocated from
 675 ** the lookaside buffer belonging to database handle dbMem.
 676 */
 677 static void fkTriggerDelete(sqlite3 *dbMem, Trigger *p){
 678   if( p ){
 679     TriggerStep *pStep = p->step_list;
 680     sqlite3ExprDelete(dbMem, pStep->pWhere);
 681     sqlite3ExprListDelete(dbMem, pStep->pExprList);
 682     sqlite3SelectDelete(dbMem, pStep->pSelect);
 683     sqlite3ExprDelete(dbMem, p->pWhen);
 684     sqlite3DbFree(dbMem, p);
 685   }
 686 }
 687
 688 /*
 689 ** This function is called to generate code that runs when table pTab is
 690 ** being dropped from the database. The SrcList passed as the second argument
 691 ** to this function contains a single entry guaranteed to resolve to
 692 ** table pTab.
 693 **
 694 ** Normally, no code is required. However, if either
 695 **
 696 **   (a) The table is the parent table of a FK constraint, or
 697 **   (b) The table is the child table of a deferred FK constraint and it is
 698 **       determined at runtime that there are outstanding deferred FK
 699 **       constraint violations in the database,
 700 **
 701 ** then the equivalent of "DELETE FROM <tbl>" is executed before dropping
 702 ** the table from the database. Triggers are disabled while running this
 703 ** DELETE, but foreign key actions are not.
 704 */
 705 void sqlite3FkDropTable(Parse *pParse, SrcList *pName, Table *pTab){
 706   sqlite3 *db = pParse->db;
 707   if( (db->flags&SQLITE_ForeignKeys) && !IsVirtual(pTab) && !pTab->pSelect ){
 708     int iSkip = 0;
 709     Vdbe *v = sqlite3GetVdbe(pParse);
 710
 711     assert( v );                  /* VDBE has already been allocated */
 712     if( sqlite3FkReferences(pTab)==0 ){
 713       /* Search for a deferred foreign key constraint for which this table
 714       ** is the child table. If one cannot be found, return without
 715       ** generating any VDBE code. If one can be found, then jump over
 716       ** the entire DELETE if there are no outstanding deferred constraints
 717       ** when this statement is run.  */
 718       FKey *p;
 719       for(p=pTab->pFKey; p; p=p->pNextFrom){
 720         if( p->isDeferred || (db->flags & SQLITE_DeferFKs) ) break;
 721       }
 722       if( !p ) return;
 723       iSkip = sqlite3VdbeMakeLabel(v);
 724       sqlite3VdbeAddOp2(v, OP_FkIfZero, 1, iSkip); VdbeCoverage(v);
 725     }
 726
 727     pParse->disableTriggers = 1;
 728     sqlite3DeleteFrom(pParse, sqlite3SrcListDup(db, pName, 0), 0, 0, 0);
 729     pParse->disableTriggers = 0;
 730
 731     /* If the DELETE has generated immediate foreign key constraint
 732     ** violations, halt the VDBE and return an error at this point, before
 733     ** any modifications to the schema are made. This is because statement
 734     ** transactions are not able to rollback schema changes.
 735     **
 736     ** If the SQLITE_DeferFKs flag is set, then this is not required, as
 737     ** the statement transaction will not be rolled back even if FK
 738     ** constraints are violated.
 739     */
 740     if( (db->flags & SQLITE_DeferFKs)==0 ){
 741       sqlite3VdbeAddOp2(v, OP_FkIfZero, 0, sqlite3VdbeCurrentAddr(v)+2);
 742       VdbeCoverage(v);
 743       sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
 744           OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
 745     }
 746
 747     if( iSkip ){
 748       sqlite3VdbeResolveLabel(v, iSkip);
 749     }
 750   }
 751 }
 752
 753
 754 /*
 755 ** The second argument points to an FKey object representing a foreign key
 756 ** for which pTab is the child table. An UPDATE statement against pTab
 757 ** is currently being processed. For each column of the table that is
 758 ** actually updated, the corresponding element in the aChange[] array
 759 ** is zero or greater (if a column is unmodified the corresponding element
 760 ** is set to -1). If the rowid column is modified by the UPDATE statement
 761 ** the bChngRowid argument is non-zero.
 762 **
 763 ** This function returns true if any of the columns that are part of the
 764 ** child key for FK constraint *p are modified.
 765 */
 766 static int fkChildIsModified(
 767   Table *pTab,                    /* Table being updated */
 768   FKey *p,                        /* Foreign key for which pTab is the child */
 769   int *aChange,                   /* Array indicating modified columns */
 770   int bChngRowid                  /* True if rowid is modified by this update */
 771 ){
 772   int i;
 773   for(i=0; i<p->nCol; i++){
 774     int iChildKey = p->aCol[i].iFrom;
 775     if( aChange[iChildKey]>=0 ) return 1;
 776     if( iChildKey==pTab->iPKey && bChngRowid ) return 1;
 777   }
 778   return 0;
 779 }
 780
 781 /*
 782 ** The second argument points to an FKey object representing a foreign key
 783 ** for which pTab is the parent table. An UPDATE statement against pTab
 784 ** is currently being processed. For each column of the table that is
 785 ** actually updated, the corresponding element in the aChange[] array
 786 ** is zero or greater (if a column is unmodified the corresponding element
 787 ** is set to -1). If the rowid column is modified by the UPDATE statement
 788 ** the bChngRowid argument is non-zero.
 789 **
 790 ** This function returns true if any of the columns that are part of the
 791 ** parent key for FK constraint *p are modified.
 792 */
 793 static int fkParentIsModified(
 794   Table *pTab,
 795   FKey *p,
 796   int *aChange,
 797   int bChngRowid
 798 ){
 799   int i;
 800   for(i=0; i<p->nCol; i++){
 801     char *zKey = p->aCol[i].zCol;
 802     int iKey;
 803     for(iKey=0; iKey<pTab->nCol; iKey++){
 804       if( aChange[iKey]>=0 || (iKey==pTab->iPKey && bChngRowid) ){
 805         Column *pCol = &pTab->aCol[iKey];
 806         if( zKey ){
 807           if( 0==sqlite3StrICmp(pCol->zName, zKey) ) return 1;
 808         }else if( pCol->colFlags & COLFLAG_PRIMKEY ){
 809           return 1;
 810         }
 811       }
 812     }
 813   }
 814   return 0;
 815 }
 816
 817 /*
 818 ** Return true if the parser passed as the first argument is being
 819 ** used to code a trigger that is really a "SET NULL" action belonging
 820 ** to trigger pFKey.
 821 */
 822 static int isSetNullAction(Parse *pParse, FKey *pFKey){
 823   Parse *pTop = sqlite3ParseToplevel(pParse);
 824   if( pTop->pTriggerPrg ){
 825     Trigger *p = pTop->pTriggerPrg->pTrigger;
 826     if( (p==pFKey->apTrigger[0] && pFKey->aAction[0]==OE_SetNull)
 827      || (p==pFKey->apTrigger[1] && pFKey->aAction[1]==OE_SetNull)
 828     ){
 829       return 1;
 830     }
 831   }
 832   return 0;
 833 }
 834
 835 /*
 836 ** This function is called when inserting, deleting or updating a row of
 837 ** table pTab to generate VDBE code to perform foreign key constraint
 838 ** processing for the operation.
 839 **
 840 ** For a DELETE operation, parameter regOld is passed the index of the
 841 ** first register in an array of (pTab->nCol+1) registers containing the
 842 ** rowid of the row being deleted, followed by each of the column values
 843 ** of the row being deleted, from left to right. Parameter regNew is passed
 844 ** zero in this case.
 845 **
 846 ** For an INSERT operation, regOld is passed zero and regNew is passed the
 847 ** first register of an array of (pTab->nCol+1) registers containing the new
 848 ** row data.
 849 **
 850 ** For an UPDATE operation, this function is called twice. Once before
 851 ** the original record is deleted from the table using the calling convention
 852 ** described for DELETE. Then again after the original record is deleted
 853 ** but before the new record is inserted using the INSERT convention.
 854 */
 855 void sqlite3FkCheck(
 856   Parse *pParse,                  /* Parse context */
 857   Table *pTab,                    /* Row is being deleted from this table */
 858   int regOld,                     /* Previous row data is stored here */
 859   int regNew,                     /* New row data is stored here */
 860   int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
 861   int bChngRowid                  /* True if rowid is UPDATEd */
 862 ){
 863   sqlite3 *db = pParse->db;       /* Database handle */
 864   FKey *pFKey;                    /* Used to iterate through FKs */
 865   int iDb;                        /* Index of database containing pTab */
 866   const char *zDb;                /* Name of database containing pTab */
 867   int isIgnoreErrors = pParse->disableTriggers;
 868
 869   /* Exactly one of regOld and regNew should be non-zero. */
 870   assert( (regOld==0)!=(regNew==0) );
 871
 872   /* If foreign-keys are disabled, this function is a no-op. */
 873   if( (db->flags&SQLITE_ForeignKeys)==0 ) return;
 874
 875   iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
 876   zDb = db->aDb[iDb].zDbSName;
 877
 878   /* Loop through all the foreign key constraints for which pTab is the
 879   ** child table (the table that the foreign key definition is part of).  */
 880   for(pFKey=pTab->pFKey; pFKey; pFKey=pFKey->pNextFrom){
 881     Table *pTo;                   /* Parent table of foreign key pFKey */
 882     Index *pIdx = 0;              /* Index on key columns in pTo */
 883     int *aiFree = 0;
 884     int *aiCol;
 885     int iCol;
 886     int i;
 887     int bIgnore = 0;
 888
 889     if( aChange
 890      && sqlite3_stricmp(pTab->zName, pFKey->zTo)!=0
 891      && fkChildIsModified(pTab, pFKey, aChange, bChngRowid)==0
 892     ){
 893       continue;
 894     }
 895
 896     /* Find the parent table of this foreign key. Also find a unique index
 897     ** on the parent key columns in the parent table. If either of these
 898     ** schema items cannot be located, set an error in pParse and return
 899     ** early.  */
 900     if( pParse->disableTriggers ){
 901       pTo = sqlite3FindTable(db, pFKey->zTo, zDb);
 902     }else{
 903       pTo = sqlite3LocateTable(pParse, 0, pFKey->zTo, zDb);
 904     }
 905     if( !pTo || sqlite3FkLocateIndex(pParse, pTo, pFKey, &pIdx, &aiFree) ){
 906       assert( isIgnoreErrors==0 || (regOld!=0 && regNew==0) );
 907       if( !isIgnoreErrors || db->mallocFailed ) return;
 908       if( pTo==0 ){
 909         /* If isIgnoreErrors is true, then a table is being dropped. In this
 910         ** case SQLite runs a "DELETE FROM xxx" on the table being dropped
 911         ** before actually dropping it in order to check FK constraints.
 912         ** If the parent table of an FK constraint on the current table is
 913         ** missing, behave as if it is empty. i.e. decrement the relevant
 914         ** FK counter for each row of the current table with non-NULL keys.
 915         */
 916         Vdbe *v = sqlite3GetVdbe(pParse);
 917         int iJump = sqlite3VdbeCurrentAddr(v) + pFKey->nCol + 1;
 918         for(i=0; i<pFKey->nCol; i++){
 919           int iReg = pFKey->aCol[i].iFrom + regOld + 1;
 920           sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iJump); VdbeCoverage(v);
 921         }
 922         sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, -1);
 923       }
 924       continue;
 925     }
 926     assert( pFKey->nCol==1 || (aiFree && pIdx) );
 927
 928     if( aiFree ){
 929       aiCol = aiFree;
 930     }else{
 931       iCol = pFKey->aCol[0].iFrom;
 932       aiCol = &iCol;
 933     }
 934     for(i=0; i<pFKey->nCol; i++){
 935       if( aiCol[i]==pTab->iPKey ){
 936         aiCol[i] = -1;
 937       }
 938       assert( pIdx==0 || pIdx->aiColumn[i]>=0 );
 939 #ifndef SQLITE_OMIT_AUTHORIZATION
 940       /* Request permission to read the parent key columns. If the
 941       ** authorization callback returns SQLITE_IGNORE, behave as if any
 942       ** values read from the parent table are NULL. */
 943       if( db->xAuth ){
 944         int rcauth;
 945         char *zCol = pTo->aCol[pIdx ? pIdx->aiColumn[i] : pTo->iPKey].zName;
 946         rcauth = sqlite3AuthReadCol(pParse, pTo->zName, zCol, iDb);
 947         bIgnore = (rcauth==SQLITE_IGNORE);
 948       }
 949 #endif
 950     }
 951
 952     /* Take a shared-cache advisory read-lock on the parent table. Allocate
 953     ** a cursor to use to search the unique index on the parent key columns
 954     ** in the parent table.  */
 955     sqlite3TableLock(pParse, iDb, pTo->tnum, 0, pTo->zName);
 956     pParse->nTab++;
 957
 958     if( regOld!=0 ){
 959       /* A row is being removed from the child table. Search for the parent.
 960       ** If the parent does not exist, removing the child row resolves an
 961       ** outstanding foreign key constraint violation. */
 962       fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regOld, -1, bIgnore);
 963     }
 964     if( regNew!=0 && !isSetNullAction(pParse, pFKey) ){
 965       /* A row is being added to the child table. If a parent row cannot
 966       ** be found, adding the child row has violated the FK constraint.
 967       **
 968       ** If this operation is being performed as part of a trigger program
 969       ** that is actually a "SET NULL" action belonging to this very
 970       ** foreign key, then omit this scan altogether. As all child key
 971       ** values are guaranteed to be NULL, it is not possible for adding
 972       ** this row to cause an FK violation.  */
 973       fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regNew, +1, bIgnore);
 974     }
 975
 976     sqlite3DbFree(db, aiFree);
 977   }
 978
 979   /* Loop through all the foreign key constraints that refer to this table.
 980   ** (the "child" constraints) */
 981   for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
 982     Index *pIdx = 0;              /* Foreign key index for pFKey */
 983     SrcList *pSrc;
 984     int *aiCol = 0;
 985
 986     if( aChange && fkParentIsModified(pTab, pFKey, aChange, bChngRowid)==0 ){
 987       continue;
 988     }
 989
 990     if( !pFKey->isDeferred && !(db->flags & SQLITE_DeferFKs)
 991      && !pParse->pToplevel && !pParse->isMultiWrite
 992     ){
 993       assert( regOld==0 && regNew!=0 );
 994       /* Inserting a single row into a parent table cannot cause (or fix)
 995       ** an immediate foreign key violation. So do nothing in this case.  */
 996       continue;
 997     }
 998
 999     if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ){
1000       if( !isIgnoreErrors || db->mallocFailed ) return;
1001       continue;
1002     }
1003     assert( aiCol || pFKey->nCol==1 );
1004
1005     /* Create a SrcList structure containing the child table.  We need the
1006     ** child table as a SrcList for sqlite3WhereBegin() */
1007     pSrc = sqlite3SrcListAppend(db, 0, 0, 0);
1008     if( pSrc ){
1009       struct SrcList_item *pItem = pSrc->a;
1010       pItem->pTab = pFKey->pFrom;
1011       pItem->zName = pFKey->pFrom->zName;
1012       pItem->pTab->nTabRef++;
1013       pItem->iCursor = pParse->nTab++;
1014
1015       if( regNew!=0 ){
1016         fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regNew, -1);
1017       }
1018       if( regOld!=0 ){
1019         int eAction = pFKey->aAction[aChange!=0];
1020         fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regOld, 1);
1021         /* If this is a deferred FK constraint, or a CASCADE or SET NULL
1022         ** action applies, then any foreign key violations caused by
1023         ** removing the parent key will be rectified by the action trigger.
1024         ** So do not set the "may-abort" flag in this case.
1025         **
1026         ** Note 1: If the FK is declared "ON UPDATE CASCADE", then the
1027         ** may-abort flag will eventually be set on this statement anyway
1028         ** (when this function is called as part of processing the UPDATE
1029         ** within the action trigger).
1030         **
1031         ** Note 2: At first glance it may seem like SQLite could simply omit
1032         ** all OP_FkCounter related scans when either CASCADE or SET NULL
1033         ** applies. The trouble starts if the CASCADE or SET NULL action
1034         ** trigger causes other triggers or action rules attached to the
1035         ** child table to fire. In these cases the fk constraint counters
1036         ** might be set incorrectly if any OP_FkCounter related scans are
1037         ** omitted.  */
1038         if( !pFKey->isDeferred && eAction!=OE_Cascade && eAction!=OE_SetNull ){
1039           sqlite3MayAbort(pParse);
1040         }
1041       }
1042       pItem->zName = 0;
1043       sqlite3SrcListDelete(db, pSrc);
1044     }
1045     sqlite3DbFree(db, aiCol);
1046   }
1047 }
1048
1049 #define COLUMN_MASK(x) (((x)>31) ? 0xffffffff : ((u32)1<<(x)))
1050
1051 /*
1052 ** This function is called before generating code to update or delete a
1053 ** row contained in table pTab.
1054 */
1055 u32 sqlite3FkOldmask(
1056   Parse *pParse,                  /* Parse context */
1057   Table *pTab                     /* Table being modified */
1058 ){
1059   u32 mask = 0;
1060   if( pParse->db->flags&SQLITE_ForeignKeys ){
1061     FKey *p;
1062     int i;
1063     for(p=pTab->pFKey; p; p=p->pNextFrom){
1064       for(i=0; i<p->nCol; i++) mask |= COLUMN_MASK(p->aCol[i].iFrom);
1065     }
1066     for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
1067       Index *pIdx = 0;
1068       sqlite3FkLocateIndex(pParse, pTab, p, &pIdx, 0);
1069       if( pIdx ){
1070         for(i=0; i<pIdx->nKeyCol; i++){
1071           assert( pIdx->aiColumn[i]>=0 );
1072           mask |= COLUMN_MASK(pIdx->aiColumn[i]);
1073         }
1074       }
1075     }
1076   }
1077   return mask;
1078 }
1079
1080
1081 /*
1082 ** This function is called before generating code to update or delete a
1083 ** row contained in table pTab. If the operation is a DELETE, then
1084 ** parameter aChange is passed a NULL value. For an UPDATE, aChange points
1085 ** to an array of size N, where N is the number of columns in table pTab.
1086 ** If the i'th column is not modified by the UPDATE, then the corresponding
1087 ** entry in the aChange[] array is set to -1. If the column is modified,
1088 ** the value is 0 or greater. Parameter chngRowid is set to true if the
1089 ** UPDATE statement modifies the rowid fields of the table.
1090 **
1091 ** If any foreign key processing will be required, this function returns
1092 ** non-zero. If there is no foreign key related processing, this function
1093 ** returns zero.
1094 **
1095 ** For an UPDATE, this function returns 2 if:
1096 **
1097 **   * There are any FKs for which pTab is the child and the parent table, or
1098 **   * the UPDATE modifies one or more parent keys for which the action is
1099 **     not "NO ACTION" (i.e. is CASCADE, SET DEFAULT or SET NULL).
1100 **
1101 ** Or, assuming some other foreign key processing is required, 1.
1102 */
1103 int sqlite3FkRequired(
1104   Parse *pParse,                  /* Parse context */
1105   Table *pTab,                    /* Table being modified */
1106   int *aChange,                   /* Non-NULL for UPDATE operations */
1107   int chngRowid                   /* True for UPDATE that affects rowid */
1108 ){
1109   int eRet = 0;
1110   if( pParse->db->flags&SQLITE_ForeignKeys ){
1111     if( !aChange ){
1112       /* A DELETE operation. Foreign key processing is required if the
1113       ** table in question is either the child or parent table for any
1114       ** foreign key constraint.  */
1115       eRet = (sqlite3FkReferences(pTab) || pTab->pFKey);
1116     }else{
1117       /* This is an UPDATE. Foreign key processing is only required if the
1118       ** operation modifies one or more child or parent key columns. */
1119       FKey *p;
1120
1121       /* Check if any child key columns are being modified. */
1122       for(p=pTab->pFKey; p; p=p->pNextFrom){
1123         if( 0==sqlite3_stricmp(pTab->zName, p->zTo) ) return 2;
1124         if( fkChildIsModified(pTab, p, aChange, chngRowid) ){
1125           eRet = 1;
1126         }
1127       }
1128
1129       /* Check if any parent key columns are being modified. */
1130       for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
1131         if( fkParentIsModified(pTab, p, aChange, chngRowid) ){
1132           if( p->aAction[1]!=OE_None ) return 2;
1133           eRet = 1;
1134         }
1135       }
1136     }
1137   }
1138   return eRet;
1139 }
1140
1141 /*
1142 ** This function is called when an UPDATE or DELETE operation is being
1143 ** compiled on table pTab, which is the parent table of foreign-key pFKey.
1144 ** If the current operation is an UPDATE, then the pChanges parameter is
1145 ** passed a pointer to the list of columns being modified. If it is a
1146 ** DELETE, pChanges is passed a NULL pointer.
1147 **
1148 ** It returns a pointer to a Trigger structure containing a trigger
1149 ** equivalent to the ON UPDATE or ON DELETE action specified by pFKey.
1150 ** If the action is "NO ACTION" or "RESTRICT", then a NULL pointer is
1151 ** returned (these actions require no special handling by the triggers
1152 ** sub-system, code for them is created by fkScanChildren()).
1153 **
1154 ** For example, if pFKey is the foreign key and pTab is table "p" in
1155 ** the following schema:
1156 **
1157 **   CREATE TABLE p(pk PRIMARY KEY);
1158 **   CREATE TABLE c(ck REFERENCES p ON DELETE CASCADE);
1159 **
1160 ** then the returned trigger structure is equivalent to:
1161 **
1162 **   CREATE TRIGGER ... DELETE ON p BEGIN
1163 **     DELETE FROM c WHERE ck = old.pk;
1164 **   END;
1165 **
1166 ** The returned pointer is cached as part of the foreign key object. It
1167 ** is eventually freed along with the rest of the foreign key object by
1168 ** sqlite3FkDelete().
1169 */
1170 static Trigger *fkActionTrigger(
1171   Parse *pParse,                  /* Parse context */
1172   Table *pTab,                    /* Table being updated or deleted from */
1173   FKey *pFKey,                    /* Foreign key to get action for */
1174   ExprList *pChanges              /* Change-list for UPDATE, NULL for DELETE */
1175 ){
1176   sqlite3 *db = pParse->db;       /* Database handle */
1177   int action;                     /* One of OE_None, OE_Cascade etc. */
1178   Trigger *pTrigger;              /* Trigger definition to return */
1179   int iAction = (pChanges!=0);    /* 1 for UPDATE, 0 for DELETE */
1180
1181   action = pFKey->aAction[iAction];
1182   if( action==OE_Restrict && (db->flags & SQLITE_DeferFKs) ){
1183     return 0;
1184   }
1185   pTrigger = pFKey->apTrigger[iAction];
1186
1187   if( action!=OE_None && !pTrigger ){
1188     char const *zFrom;            /* Name of child table */
1189     int nFrom;                    /* Length in bytes of zFrom */
1190     Index *pIdx = 0;              /* Parent key index for this FK */
1191     int *aiCol = 0;               /* child table cols -> parent key cols */
1192     TriggerStep *pStep = 0;        /* First (only) step of trigger program */
1193     Expr *pWhere = 0;             /* WHERE clause of trigger step */
1194     ExprList *pList = 0;          /* Changes list if ON UPDATE CASCADE */
1195     Select *pSelect = 0;          /* If RESTRICT, "SELECT RAISE(...)" */
1196     int i;                        /* Iterator variable */
1197     Expr *pWhen = 0;              /* WHEN clause for the trigger */
1198
1199     if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ) return 0;
1200     assert( aiCol || pFKey->nCol==1 );
1201
1202     for(i=0; i<pFKey->nCol; i++){
1203       Token tOld = { "old", 3 };  /* Literal "old" token */
1204       Token tNew = { "new", 3 };  /* Literal "new" token */
1205       Token tFromCol;             /* Name of column in child table */
1206       Token tToCol;               /* Name of column in parent table */
1207       int iFromCol;               /* Idx of column in child table */
1208       Expr *pEq;                  /* tFromCol = OLD.tToCol */
1209
1210       iFromCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
1211       assert( iFromCol>=0 );
1212       assert( pIdx!=0 || (pTab->iPKey>=0 && pTab->iPKey<pTab->nCol) );
1213       assert( pIdx==0 || pIdx->aiColumn[i]>=0 );
1214       sqlite3TokenInit(&tToCol,
1215                    pTab->aCol[pIdx ? pIdx->aiColumn[i] : pTab->iPKey].zName);
1216       sqlite3TokenInit(&tFromCol, pFKey->pFrom->aCol[iFromCol].zName);
1217
1218       /* Create the expression "OLD.zToCol = zFromCol". It is important
1219       ** that the "OLD.zToCol" term is on the LHS of the = operator, so
1220       ** that the affinity and collation sequence associated with the
1221       ** parent table are used for the comparison. */
1222       pEq = sqlite3PExpr(pParse, TK_EQ,
1223           sqlite3PExpr(pParse, TK_DOT,
1224             sqlite3ExprAlloc(db, TK_ID, &tOld, 0),
1225             sqlite3ExprAlloc(db, TK_ID, &tToCol, 0)),
1226           sqlite3ExprAlloc(db, TK_ID, &tFromCol, 0)
1227       );
1228       pWhere = sqlite3ExprAnd(db, pWhere, pEq);
1229
1230       /* For ON UPDATE, construct the next term of the WHEN clause.
1231       ** The final WHEN clause will be like this:
1232       **
1233       **    WHEN NOT(old.col1 IS new.col1 AND ... AND old.colN IS new.colN)
1234       */
1235       if( pChanges ){
1236         pEq = sqlite3PExpr(pParse, TK_IS,
1237             sqlite3PExpr(pParse, TK_DOT,
1238               sqlite3ExprAlloc(db, TK_ID, &tOld, 0),
1239               sqlite3ExprAlloc(db, TK_ID, &tToCol, 0)),
1240             sqlite3PExpr(pParse, TK_DOT,
1241               sqlite3ExprAlloc(db, TK_ID, &tNew, 0),
1242               sqlite3ExprAlloc(db, TK_ID, &tToCol, 0))
1243             );
1244         pWhen = sqlite3ExprAnd(db, pWhen, pEq);
1245       }
1246
1247       if( action!=OE_Restrict && (action!=OE_Cascade || pChanges) ){
1248         Expr *pNew;
1249         if( action==OE_Cascade ){
1250           pNew = sqlite3PExpr(pParse, TK_DOT,
1251             sqlite3ExprAlloc(db, TK_ID, &tNew, 0),
1252             sqlite3ExprAlloc(db, TK_ID, &tToCol, 0));
1253         }else if( action==OE_SetDflt ){
1254           Expr *pDflt = pFKey->pFrom->aCol[iFromCol].pDflt;
1255           if( pDflt ){
1256             pNew = sqlite3ExprDup(db, pDflt, 0);
1257           }else{
1258             pNew = sqlite3ExprAlloc(db, TK_NULL, 0, 0);
1259           }
1260         }else{
1261           pNew = sqlite3ExprAlloc(db, TK_NULL, 0, 0);
1262         }
1263         pList = sqlite3ExprListAppend(pParse, pList, pNew);
1264         sqlite3ExprListSetName(pParse, pList, &tFromCol, 0);
1265       }
1266     }
1267     sqlite3DbFree(db, aiCol);
1268
1269     zFrom = pFKey->pFrom->zName;
1270     nFrom = sqlite3Strlen30(zFrom);
1271
1272     if( action==OE_Restrict ){
1273       Token tFrom;
1274       Expr *pRaise;
1275
1276       tFrom.z = zFrom;
1277       tFrom.n = nFrom;
1278       pRaise = sqlite3Expr(db, TK_RAISE, "FOREIGN KEY constraint failed");
1279       if( pRaise ){
1280         pRaise->affinity = OE_Abort;
1281       }
1282       pSelect = sqlite3SelectNew(pParse,
1283           sqlite3ExprListAppend(pParse, 0, pRaise),
1284           sqlite3SrcListAppend(db, 0, &tFrom, 0),
1285           pWhere,
1286           0, 0, 0, 0, 0
1287       );
1288       pWhere = 0;
1289     }
1290
1291     /* Disable lookaside memory allocation */
1292     db->lookaside.bDisable++;
1293
1294     pTrigger = (Trigger *)sqlite3DbMallocZero(db,
1295         sizeof(Trigger) +         /* struct Trigger */
1296         sizeof(TriggerStep) +     /* Single step in trigger program */
1297         nFrom + 1                 /* Space for pStep->zTarget */
1298     );
1299     if( pTrigger ){
1300       pStep = pTrigger->step_list = (TriggerStep *)&pTrigger[1];
1301       pStep->zTarget = (char *)&pStep[1];
1302       memcpy((char *)pStep->zTarget, zFrom, nFrom);
1303
1304       pStep->pWhere = sqlite3ExprDup(db, pWhere, EXPRDUP_REDUCE);
1305       pStep->pExprList = sqlite3ExprListDup(db, pList, EXPRDUP_REDUCE);
1306       pStep->pSelect = sqlite3SelectDup(db, pSelect, EXPRDUP_REDUCE);
1307       if( pWhen ){
1308         pWhen = sqlite3PExpr(pParse, TK_NOT, pWhen, 0);
1309         pTrigger->pWhen = sqlite3ExprDup(db, pWhen, EXPRDUP_REDUCE);
1310       }
1311     }
1312
1313     /* Re-enable the lookaside buffer, if it was disabled earlier. */
1314     db->lookaside.bDisable--;
1315
1316     sqlite3ExprDelete(db, pWhere);
1317     sqlite3ExprDelete(db, pWhen);
1318     sqlite3ExprListDelete(db, pList);
1319     sqlite3SelectDelete(db, pSelect);
1320     if( db->mallocFailed==1 ){
1321       fkTriggerDelete(db, pTrigger);
1322       return 0;
1323     }
1324     assert( pStep!=0 );
1325
1326     switch( action ){
1327       case OE_Restrict:
1328         pStep->op = TK_SELECT;
1329         break;
1330       case OE_Cascade:
1331         if( !pChanges ){
1332           pStep->op = TK_DELETE;
1333           break;
1334         }
1335       default:
1336         pStep->op = TK_UPDATE;
1337     }
1338     pStep->pTrig = pTrigger;
1339     pTrigger->pSchema = pTab->pSchema;
1340     pTrigger->pTabSchema = pTab->pSchema;
1341     pFKey->apTrigger[iAction] = pTrigger;
1342     pTrigger->op = (pChanges ? TK_UPDATE : TK_DELETE);
1343   }
1344
1345   return pTrigger;
1346 }
1347
1348 /*
1349 ** This function is called when deleting or updating a row to implement
1350 ** any required CASCADE, SET NULL or SET DEFAULT actions.
1351 */
1352 void sqlite3FkActions(
1353   Parse *pParse,                  /* Parse context */
1354   Table *pTab,                    /* Table being updated or deleted from */
1355   ExprList *pChanges,             /* Change-list for UPDATE, NULL for DELETE */
1356   int regOld,                     /* Address of array containing old row */
1357   int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
1358   int bChngRowid                  /* True if rowid is UPDATEd */
1359 ){
1360   /* If foreign-key support is enabled, iterate through all FKs that
1361   ** refer to table pTab. If there is an action associated with the FK
1362   ** for this operation (either update or delete), invoke the associated
1363   ** trigger sub-program.  */
1364   if( pParse->db->flags&SQLITE_ForeignKeys ){
1365     FKey *pFKey;                  /* Iterator variable */
1366     for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
1367       if( aChange==0 || fkParentIsModified(pTab, pFKey, aChange, bChngRowid) ){
1368         Trigger *pAct = fkActionTrigger(pParse, pTab, pFKey, pChanges);
1369         if( pAct ){
1370           sqlite3CodeRowTriggerDirect(pParse, pAct, pTab, regOld, OE_Abort, 0);
1371         }
1372       }
1373     }
1374   }
1375 }
1376
1377 #endif /* ifndef SQLITE_OMIT_TRIGGER */
1378
1379 /*
1380 ** Free all memory associated with foreign key definitions attached to
1381 ** table pTab. Remove the deleted foreign keys from the Schema.fkeyHash
1382 ** hash table.
1383 */
1384 void sqlite3FkDelete(sqlite3 *db, Table *pTab){
1385   FKey *pFKey;                    /* Iterator variable */
1386   FKey *pNext;                    /* Copy of pFKey->pNextFrom */
1387
1388   assert( db==0 || IsVirtual(pTab)
1389          || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
1390   for(pFKey=pTab->pFKey; pFKey; pFKey=pNext){
1391
1392     /* Remove the FK from the fkeyHash hash table. */
1393     if( !db || db->pnBytesFreed==0 ){
1394       if( pFKey->pPrevTo ){
1395         pFKey->pPrevTo->pNextTo = pFKey->pNextTo;
1396       }else{
1397         void *p = (void *)pFKey->pNextTo;
1398         const char *z = (p ? pFKey->pNextTo->zTo : pFKey->zTo);
1399         sqlite3HashInsert(&pTab->pSchema->fkeyHash, z, p);
1400       }
1401       if( pFKey->pNextTo ){
1402         pFKey->pNextTo->pPrevTo = pFKey->pPrevTo;
1403       }
1404     }
1405
1406     /* EV: R-30323-21917 Each foreign key constraint in SQLite is
1407     ** classified as either immediate or deferred.
1408     */
1409     assert( pFKey->isDeferred==0 || pFKey->isDeferred==1 );
1410
1411     /* Delete any triggers created to implement actions for this FK. */
1412 #ifndef SQLITE_OMIT_TRIGGER
1413     fkTriggerDelete(db, pFKey->apTrigger[0]);
1414     fkTriggerDelete(db, pFKey->apTrigger[1]);
1415 #endif
1416
1417     pNext = pFKey->pNextFrom;
1418     sqlite3DbFree(db, pFKey);
1419   }
1420 }
1421 #endif /* ifndef SQLITE_OMIT_FOREIGN_KEY */