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/**
* Copyright (C) 2014 MongoDB 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/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/platform/basic.h"
#include <ostream>
#include "mongo/db/jsobj.h"
#include "mongo/db/storage/index_entry_comparison.h"
namespace mongo {
std::ostream& operator<<(std::ostream& stream, const IndexKeyEntry& entry) {
return stream << entry.key << '@' << entry.loc;
}
// Due to the limitations of various APIs, we need to use the same type (IndexKeyEntry)
// for both the stored data and the "query". We cheat and encode extra information in the
// first byte of the field names in the query. This works because all stored objects should
// have all field names empty, so their first bytes are '\0'.
enum BehaviorIfFieldIsEqual {
normal = '\0',
less = 'l',
greater = 'g',
};
bool IndexEntryComparison::operator() (const IndexKeyEntry& lhs, const IndexKeyEntry& rhs)
const {
// implementing in memcmp style to ease reuse of this code.
return compare(lhs, rhs) < 0;
}
// This should behave the same as customBSONCmp from btree_logic.cpp.
//
// Reading the comment in the .h file is highly recommended if you need to understand what this
// function is doing
int IndexEntryComparison::compare(const IndexKeyEntry& lhs, const IndexKeyEntry& rhs) const {
BSONObjIterator lhsIt(lhs.key);
BSONObjIterator rhsIt(rhs.key);
// Iterate through both BSONObjects, comparing individual elements one by one
for (unsigned mask = 1; lhsIt.more(); mask <<= 1) {
if (!rhsIt.more())
return _order.descending(mask) ? -1 : 1;
const BSONElement l = lhsIt.next();
const BSONElement r = rhsIt.next();
if (int cmp = l.woCompare(r, /*compareFieldNames=*/false)) {
if (cmp == std::numeric_limits<int>::min()) {
// can't be negated
cmp = -1;
}
return _order.descending(mask) ? -cmp : cmp;
}
// Here is where the weirdness begins. We sometimes want to fudge the comparison
// when a key == the query to implement exclusive ranges.
BehaviorIfFieldIsEqual lEqBehavior = BehaviorIfFieldIsEqual(l.fieldName()[0]);
BehaviorIfFieldIsEqual rEqBehavior = BehaviorIfFieldIsEqual(r.fieldName()[0]);
if (lEqBehavior) {
// lhs is the query, rhs is the stored data
invariant(rEqBehavior == normal);
return lEqBehavior == less ? -1 : 1;
}
if (rEqBehavior) {
// rhs is the query, lhs is the stored data, so reverse the returns
invariant(lEqBehavior == normal);
return rEqBehavior == less ? 1 : -1;
}
}
if(rhsIt.more())
return -1;
// This means just look at the key, not the loc.
if (lhs.loc.isNull() || rhs.loc.isNull())
return 0;
return lhs.loc.compare(rhs.loc); // is supposed to ignore ordering
}
// reading the comment in the .h file is highly recommended if you need to understand what this
// function is doing
BSONObj IndexEntryComparison::makeQueryObject(const BSONObj& keyPrefix,
int prefixLen,
bool prefixExclusive,
const std::vector<const BSONElement*>& keySuffix,
const std::vector<bool>& suffixInclusive,
const int cursorDirection) {
// Please read the comments in the header file to see why this is done.
// The basic idea is that we use the field name to store a byte which indicates whether
// each field in the query object is inclusive and exclusive, and if it is exclusive, in
// which direction.
const char exclusiveByte = (cursorDirection == 1 ? greater : less);
const StringData exclusiveFieldName(&exclusiveByte, 1);
BSONObjBuilder bb;
// handle the prefix
if (prefixLen > 0) {
BSONObjIterator it(keyPrefix);
for (int i = 0; i < prefixLen; i++) {
invariant(it.more());
const BSONElement e = it.next();
if (prefixExclusive && i == prefixLen - 1) {
bb.appendAs(e, exclusiveFieldName);
}
else {
bb.appendAs(e, StringData());
}
}
}
// If the prefix is exclusive then the suffix does not matter as it will never be used
if (prefixExclusive) {
invariant(prefixLen > 0);
return bb.obj();
}
// Handle the suffix. Note that the useful parts of the suffix start at index prefixLen
// rather than at 0.
invariant(keySuffix.size() == suffixInclusive.size());
for (size_t i = prefixLen; i < keySuffix.size(); i++) {
invariant(keySuffix[i]);
if (suffixInclusive[i]) {
bb.appendAs(*keySuffix[i], StringData());
} else {
bb.appendAs(*keySuffix[i], exclusiveFieldName);
// If an exclusive field exists then no fields after this will matter, since an
// exclusive field never evaluates as equal
return bb.obj();
}
}
return bb.obj();
}
} // namespace mongo
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