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Improved comments on foreign key logic.

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FossilOrigin-Name: 1315d9109c7105f4a62bb2d43ca6948d41245129
This commit is contained in:
drh
2013-11-03 02:27:58 +00:00
parent 2552d43f4c
commit bd50a926ef
5 changed files with 47 additions and 36 deletions
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32
src/fkey.c
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@@ -475,12 +475,12 @@ static void fkLookupParent(
*/
static void fkScanChildren(
Parse *pParse, /* Parse context */
SrcList *pSrc, /* SrcList containing the table to scan */
Table *pTab,
Index *pIdx, /* Foreign key index */
FKey *pFKey, /* Foreign key relationship */
SrcList *pSrc, /* The child table to be scanned */
Table *pTab, /* The parent table */
Index *pIdx, /* Index on parent covering the foreign key */
FKey *pFKey, /* The foreign key linking pSrc to pTab */
int *aiCol, /* Map from pIdx cols to child table cols */
int regData, /* Referenced table data starts here */
int regData, /* Parent row data starts here */
int nIncr /* Amount to increment deferred counter by */
){
sqlite3 *db = pParse->db; /* Database handle */
@@ -491,7 +491,9 @@ static void fkScanChildren(
int iFkIfZero = 0; /* Address of OP_FkIfZero */
Vdbe *v = sqlite3GetVdbe(pParse);
assert( !pIdx || pIdx->pTable==pTab );
assert( pIdx==0 || pIdx->pTable==pTab );
assert( pIdx==0 || pIdx->nKeyCol==pFKey->nCol );
assert( pIdx!=0 || pFKey->nCol==1 );
if( nIncr<0 ){
iFkIfZero = sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, 0);
@@ -545,7 +547,7 @@ static void fkScanChildren(
** row being deleted from the scan by adding ($rowid != rowid) to the WHERE
** clause, where $rowid is the rowid of the row being deleted. */
if( pTab==pFKey->pFrom && nIncr>0 && HasRowid(pTab) /*FIXME*/ ){
Expr *pEq; /* Expression (pLeft = pRight) */
Expr *pNe; /* Expression (pLeft != pRight) */
Expr *pLeft; /* Value from parent table row */
Expr *pRight; /* Column ref to child table */
pLeft = sqlite3Expr(db, TK_REGISTER, 0);
@@ -556,8 +558,8 @@ static void fkScanChildren(
pRight->iTable = pSrc->a[0].iCursor;
pRight->iColumn = -1;
}
pEq = sqlite3PExpr(pParse, TK_NE, pLeft, pRight, 0);
pWhere = sqlite3ExprAnd(db, pWhere, pEq);
pNe = sqlite3PExpr(pParse, TK_NE, pLeft, pRight, 0);
pWhere = sqlite3ExprAnd(db, pWhere, pNe);
}
/* Resolve the references in the WHERE clause. */
@@ -587,8 +589,8 @@ static void fkScanChildren(
}
/*
** This function returns a pointer to the head of a linked list of FK
** constraints for which table pTab is the parent table. For example,
** This function returns a linked list of FKey objects (connected by
** FKey.pNextTo) holding all children of table pTab. For example,
** given the following schema:
**
** CREATE TABLE t1(a PRIMARY KEY);
@@ -890,7 +892,8 @@ void sqlite3FkCheck(
sqlite3DbFree(db, aiFree);
}
/* Loop through all the foreign key constraints that refer to this table */
/* Loop through all the foreign key constraints that refer to this table.
** (the "child" constraints) */
for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
Index *pIdx = 0; /* Foreign key index for pFKey */
SrcList *pSrc;
@@ -915,9 +918,8 @@ void sqlite3FkCheck(
}
assert( aiCol || pFKey->nCol==1 );
/* Create a SrcList structure containing a single table (the table
** the foreign key that refers to this table is attached to). This
** is required for the sqlite3WhereXXX() interface. */
/* Create a SrcList structure containing the child table. We need the
** child table as a SrcList for sqlite3WhereBegin() */
pSrc = sqlite3SrcListAppend(db, 0, 0, 0);
if( pSrc ){
struct SrcList_item *pItem = pSrc->a;