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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 isIndexOnOwnFieldTypeNode(me);
}
/**
* This array operator doesn't have any children with fields and can use an index.
*
* Example: a: {$elemMatch: {$gte: 1, $lte: 1}}.
*/
static bool arrayUsesIndexOnOwnField(const MatchExpression* me) {
if (!me->isArray()) {
return false;
}
if (MatchExpression::ELEM_MATCH_VALUE != me->matchType()) {
return false;
}
// We have an ELEM_MATCH_VALUE expression. In order to be
// considered "indexable" all children of the ELEM_MATCH_VALUE
// must be "indexable" type expressions as well.
for (size_t i = 0; i < me->numChildren(); i++) {
MatchExpression* child = me->getChild(i);
// Special case for NOT: If the child is a NOT, then it's the thing below
// the NOT that we care about.
if (MatchExpression::NOT == child->matchType()) {
MatchExpression* notChild = child->getChild(0);
if (MatchExpression::MOD == notChild->matchType() ||
MatchExpression::REGEX == notChild->matchType() ||
MatchExpression::TYPE_OPERATOR == notChild->matchType()) {
// We can't index negations of this kind of expression node.
return false;
}
// It's the child of the NOT that we check for indexability.
if (!isIndexOnOwnFieldTypeNode(notChild)) {
return false;
}
// Special handling for NOT has already been done; don't fall through.
continue;
}
if (!isIndexOnOwnFieldTypeNode(child)) {
return false;
}
}
// The entire ELEM_MATCH_VALUE is indexable since every one of its children
// is indexable.
return true;
}
/**
* Certain array operators require that the field for that operator is prepended
* to all fields in that operator's children.
*
* Example: a: {$elemMatch: {b:1, c:1}}.
*/
static bool arrayUsesIndexOnChildren(const MatchExpression* me) {
return me->isArray() && MatchExpression::ELEM_MATCH_OBJECT == me->matchType();
}
/**
* 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);
}
private:
/**
* Returns true if 'me' is "sargable" but is not a negation and
* is not an array node such as ELEM_MATCH_VALUE.
*
* Used as a helper for nodeCanUseIndexOnOwnField().
*/
static bool isIndexOnOwnFieldTypeNode(const MatchExpression* me) {
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::EXISTS || me->matchType() == MatchExpression::TEXT;
}
};
} // namespace mongo
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