Status HashIndexCursor::seek(const BSONObj& position) {
//Use FieldRangeSet to parse the query into a vector of intervals
//These should be point-intervals if this cursor is ever used
//So the FieldInterval vector will be, e.g. <[1,1], [3,3], [6,6]>
FieldRangeSet frs( "" , position, true, true );
const vector<FieldInterval>& intervals = frs.range( _hashedField.c_str() ).intervals();
//Construct a new query based on the hashes of the previous point-intervals
//e.g. {a : {$in : [ hash(1) , hash(3) , hash(6) ]}}
BSONObjBuilder newQueryBuilder;
BSONObjBuilder inObj( newQueryBuilder.subobjStart( _hashedField ) );
BSONArrayBuilder inArray( inObj.subarrayStart("$in") );
vector<FieldInterval>::const_iterator i;
for( i = intervals.begin(); i != intervals.end(); ++i ){
if ( ! i->equality() ){
_oldCursor.reset(
BtreeCursor::make( nsdetails( _descriptor->parentNS()),
_descriptor->getOnDisk(),
BSON( "" << MINKEY ) ,
BSON( "" << MAXKEY ) ,
true ,
1 ) );
return Status::OK();
}
inArray.append(HashAccessMethod::makeSingleKey(i->_lower._bound, _seed, _hashVersion));
}
inArray.done();
inObj.done();
BSONObj newQuery = newQueryBuilder.obj();
// FieldRangeVector needs an IndexSpec so we make it one.
BSONObjBuilder specBuilder;
BSONObjIterator it(_descriptor->keyPattern());
while (it.more()) {
BSONElement e = it.next();
specBuilder.append(e.fieldName(), 1);
}
BSONObj spec = specBuilder.obj();
IndexSpec specForFRV(spec);
//Use the point-intervals of the new query to create a Btree cursor
FieldRangeSet newfrs( "" , newQuery , true, true );
shared_ptr<FieldRangeVector> newVector(
new FieldRangeVector( newfrs , specForFRV, 1 ) );
_oldCursor.reset(
BtreeCursor::make(nsdetails(_descriptor->parentNS()),
_descriptor->getOnDisk(),
newVector,
0,
1));
return Status::OK();
}
shared_ptr<Cursor> HashedIndexType::newCursor( const BSONObj& query ,
const BSONObj& order , int numWanted ) const {
//Use FieldRangeSet to parse the query into a vector of intervals
//These should be point-intervals if this cursor is ever used
//So the FieldInterval vector will be, e.g. <[1,1], [3,3], [6,6]>
FieldRangeSet frs( "" , query , true, true );
const vector<FieldInterval>& intervals = frs.range( _hashedField.c_str() ).intervals();
//Force a match of the query against the actual document by giving
//the cursor a matcher with an empty indexKeyPattern. This insures the
//index is not used as a covered index.
//NOTE: this forcing is necessary due to potential hash collisions
const shared_ptr< CoveredIndexMatcher > forceDocMatcher(
new CoveredIndexMatcher( query , BSONObj() ) );
//Construct a new query based on the hashes of the previous point-intervals
//e.g. {a : {$in : [ hash(1) , hash(3) , hash(6) ]}}
BSONObjBuilder newQueryBuilder;
BSONObjBuilder inObj( newQueryBuilder.subobjStart( _hashedField ) );
BSONArrayBuilder inArray( inObj.subarrayStart("$in") );
vector<FieldInterval>::const_iterator i;
for( i = intervals.begin(); i != intervals.end(); ++i ){
if ( ! i->equality() ){
const shared_ptr< BtreeCursor > exhaustiveCursor(
BtreeCursor::make( nsdetails( _spec->getDetails()->parentNS().c_str()),
*( _spec->getDetails() ),
BSON( "" << MINKEY ) ,
BSON( "" << MAXKEY ) ,
true ,
1 ) );
exhaustiveCursor->setMatcher( forceDocMatcher );
return exhaustiveCursor;
}
inArray.append( makeSingleKey( i->_lower._bound , _seed , _hashVersion ) );
}
inArray.done();
inObj.done();
BSONObj newQuery = newQueryBuilder.obj();
//Use the point-intervals of the new query to create a Btree cursor
FieldRangeSet newfrs( "" , newQuery , true, true );
shared_ptr<FieldRangeVector> newVector(
new FieldRangeVector( newfrs , *_spec , 1 ) );
const shared_ptr< BtreeCursor > cursor(
BtreeCursor::make( nsdetails( _spec->getDetails()->parentNS().c_str()),
*( _spec->getDetails() ), newVector , 1 ) );
cursor->setMatcher( forceDocMatcher );
return cursor;
}
