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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/>.
*
* 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/db/matcher/expression.h"
#pragma once
namespace mongo {
/**
* Logic for how indices can be used with an expression.
*/
class Indexability {
public:
/**
* Is an index over me->path() useful?
* This is the same thing as being sargable, if you have a RDBMS background.
*/
static bool nodeCanUseIndexOnOwnField(const MatchExpression* me) {
if (me->path().empty()) {
return false;
}
if (arrayUsesIndexOnOwnField(me)) {
return true;
}
return me->matchType() == MatchExpression::LTE
|| me->matchType() == MatchExpression::LT
|| me->matchType() == MatchExpression::EQ
|| me->matchType() == MatchExpression::GT
|| me->matchType() == MatchExpression::GTE
|| me->matchType() == MatchExpression::REGEX
|| me->matchType() == MatchExpression::MOD
|| me->matchType() == MatchExpression::MATCH_IN
|| me->matchType() == MatchExpression::TYPE_OPERATOR
|| me->matchType() == MatchExpression::GEO
|| me->matchType() == MatchExpression::GEO_NEAR
|| me->matchType() == MatchExpression::TEXT;
}
/**
* This array operator doesn't have any children with fields and can use an index.
*
* Example: a: {$elemMatch: {$gte: 1, $lte: 1}}.
*/
static bool arrayUsesIndexOnOwnField(const MatchExpression* me) {
return me->isArray() && MatchExpression::ELEM_MATCH_VALUE == me->matchType();
}
/**
* Certain array operators require that the field for that operator is prepended
* to all fields in that operator's children.
*
* Example: a: {$elemMatch: {b:1, c:1}}.
*/
static bool arrayUsesIndexOnChildren(const MatchExpression* me) {
return me->isArray() && (MatchExpression::ELEM_MATCH_OBJECT == me->matchType()
|| MatchExpression::ALL == me->matchType());
}
/**
* Returns true if 'me' is a NOT, and the child of the NOT can use
* an index on its own field.
*/
static bool isBoundsGeneratingNot(const MatchExpression* me) {
return MatchExpression::NOT == me->matchType() &&
nodeCanUseIndexOnOwnField(me->getChild(0));
}
/**
* Returns true if either 'me' is a bounds generating NOT,
* or 'me' can use an index on its own field.
*/
static bool isBoundsGenerating(const MatchExpression* me) {
return isBoundsGeneratingNot(me) || nodeCanUseIndexOnOwnField(me);
}
};
} // namespace mongo
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