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/**
* Copyright (C) 2013 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "mongo/db/btree.h"
#include "mongo/db/btreecursor.h"
#include "mongo/db/hasher.h"
#include "mongo/db/index/hash_access_method.h"
#include "mongo/db/index/hash_index_cursor.h"
#include "mongo/db/queryutil.h"
namespace mongo {
long long int HashAccessMethod::makeSingleKey(const BSONElement& e, HashSeed seed, int v) {
massert(16767, "Only HashVersion 0 has been defined" , v == 0 );
return BSONElementHasher::hash64(e, seed);
}
HashAccessMethod::HashAccessMethod(IndexDescriptor* descriptor)
: BtreeBasedAccessMethod(descriptor) {
const string HASHED_INDEX_TYPE_IDENTIFIER = "hashed";
//change these if single-field limitation lifted later
uassert(16763, "Currently only single field hashed index supported." ,
1 == descriptor->getNumFields());
uassert(16764, "Currently hashed indexes cannot guarantee uniqueness. Use a regular index.",
!descriptor->unique());
//Default _seed to 0 if "seed" is not included in the index spec
//or if the value of "seed" is not a number
_seed = descriptor->getInfoElement("seed").numberInt();
//In case we have hashed indexes based on other hash functions in
//the future, we store a hashVersion number. If hashVersion changes,
// "makeSingleKey" will need to change accordingly.
//Defaults to 0 if "hashVersion" is not included in the index spec
//or if the value of "hashversion" is not a number
_hashVersion = descriptor->getInfoElement("hashVersion").numberInt();
//Get the hashfield name
BSONElement firstElt = descriptor->keyPattern().firstElement();
massert(16765, "error: no hashed index field",
firstElt.str().compare(HASHED_INDEX_TYPE_IDENTIFIER) == 0);
_hashedField = firstElt.fieldName();
// Explicit null valued fields and missing fields are both represented in hashed indexes
// using the hash value of the null BSONElement. This is partly for historical reasons
// (hash of null was used in the initial release of hashed indexes and changing would alter
// the data format). Additionally, in certain places the hashed index code and the index
// bound calculation code assume null and missing are indexed identically.
BSONObj nullObj = BSON("" << BSONNULL);
_missingKey = BSON("" << makeSingleKey(nullObj.firstElement(), _seed, _hashVersion));
}
Status HashAccessMethod::newCursor(IndexCursor** out) {
*out = new HashIndexCursor(_hashedField, _seed, _hashVersion, _descriptor);
return Status::OK();
}
void HashAccessMethod::getKeys(const BSONObj& obj, BSONObjSet* keys) {
const char* cstr = _hashedField.c_str();
BSONElement fieldVal = obj.getFieldDottedOrArray(cstr);
uassert(16766, "Error: hashed indexes do not currently support array values",
fieldVal.type() != Array );
if (!fieldVal.eoo()) {
BSONObj key = BSON( "" << makeSingleKey( fieldVal , _seed , _hashVersion ) );
keys->insert( key );
} else if (!_descriptor->isSparse()) {
keys->insert( _missingKey.copy() );
}
}
} // namespace mongo
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