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/**
* Copyright (C) 2016 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.
*/
#pragma once
#include "mongo/platform/basic.h"
#include <boost/intrusive_ptr.hpp>
#include <memory>
#include "mongo/bson/bsonelement.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/field_path.h"
#include "mongo/db/pipeline/transformer_interface.h"
namespace mongo {
class BSONObj;
class Document;
class ExpressionContext;
namespace parsed_aggregation_projection {
/**
* This class ensures that the specification was valid: that none of the paths specified conflict
* with one another, that there is at least one field, etc. Here "projection" includes both
* $project specifications and $addFields specifications.
*/
class ProjectionSpecValidator {
public:
/**
* Throws if the specification is not valid for a projection. The stageName is used to provide a
* more helpful error message.
*/
static void uassertValid(const BSONObj& spec, StringData stageName);
private:
ProjectionSpecValidator(const BSONObj& spec) : _rawObj(spec) {}
/**
* Uses '_seenPaths' to see if 'path' conflicts with any paths that have already been specified.
*
* For example, a user is not allowed to specify {'a': 1, 'a.b': 1}, or some similar conflicting
* paths.
*/
void ensurePathDoesNotConflictOrThrow(const std::string& path);
/**
* Throws if an invalid projection specification is detected.
*/
void validate();
/**
* Parses a single BSONElement. 'pathToElem' should include the field name of 'elem'.
*
* Delegates to parseSubObject() if 'elem' is an object. Otherwise adds the full path to 'elem'
* to '_seenPaths'.
*
* Calls ensurePathDoesNotConflictOrThrow with the path to this element, throws on conflicting
* path specifications.
*/
void parseElement(const BSONElement& elem, const FieldPath& pathToElem);
/**
* Traverses 'thisLevelSpec', parsing each element in turn.
*
* Throws if any paths conflict with each other or existing paths, 'thisLevelSpec' contains a
* dotted path, or if 'thisLevelSpec' represents an invalid expression.
*/
void parseNestedObject(const BSONObj& thisLevelSpec, const FieldPath& prefix);
// The original object. Used to generate more helpful error messages.
const BSONObj& _rawObj;
// Custom comparator that orders fieldpath strings by path prefix first, then by field.
struct PathPrefixComparator {
static constexpr char dot = '.';
// Returns true if the lhs value should sort before the rhs, false otherwise.
bool operator()(const std::string& lhs, const std::string& rhs) const {
for (size_t pos = 0, len = std::min(lhs.size(), rhs.size()); pos < len; ++pos) {
auto &lchar = lhs[pos], &rchar = rhs[pos];
if (lchar == rchar) {
continue;
}
// Consider the path delimiter '.' as being less than all other characters, so that
// paths sort directly before any paths they prefix and directly after any paths
// which prefix them.
if (lchar == dot) {
return true;
} else if (rchar == dot) {
return false;
}
// Otherwise, default to normal character comparison.
return lchar < rchar;
}
// If we get here, then we have reached the end of lhs and/or rhs and all of their path
// segments up to this point match. If lhs is shorter than rhs, then lhs prefixes rhs
// and should sort before it.
return lhs.size() < rhs.size();
}
};
// Tracks which paths we've seen to ensure no two paths conflict with each other.
std::set<std::string, PathPrefixComparator> _seenPaths;
};
/**
* A ParsedAggregationProjection is responsible for parsing and executing a $project. It
* represents either an inclusion or exclusion projection. This is the common interface between the
* two types of projections.
*/
class ParsedAggregationProjection : public TransformerInterface {
public:
// Allows the caller to indicate whether the projection should default to including or excluding
// the _id field in the event that the projection spec does not specify the desired behavior.
// For instance, given a projection {a: 1}, specifying 'kExcludeId' is equivalent to projecting
// {a: 1, _id: 0} while 'kIncludeId' is equivalent to the projection {a: 1, _id: 1}. If the user
// explicitly specifies a projection on _id, then this will override the default policy; for
// instance, {a: 1, _id: 0} will exclude _id for both 'kExcludeId' and 'kIncludeId'.
enum class ProjectionDefaultIdPolicy { kIncludeId, kExcludeId };
// Allows the caller to specify how the projection should handle nested arrays; that is, an
// array whose immediate parent is itself an array. For example, in the case of sample document
// {a: [1, 2, [3, 4], {b: [5, 6]}]} the array [3, 4] is a nested array. The array [5, 6] is not,
// because there is an intervening object between it and its closest array ancestor.
enum class ProjectionArrayRecursionPolicy { kRecurseNestedArrays, kDoNotRecurseNestedArrays };
// Allows the caller to specify whether computed fields should be allowed within inclusion
// projections; they are implicitly prohibited within exclusion projections.
enum class ProjectionParseMode {
kBanComputedFields, // No computed fields are permitted in the projection spec.
kAllowComputedFields // Computed fields are permitted.
};
/**
* Main entry point for a ParsedAggregationProjection.
*
* Throws a AssertionException if 'spec' is an invalid projection specification.
*/
static std::unique_ptr<ParsedAggregationProjection> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const BSONObj& spec,
ProjectionDefaultIdPolicy defaultIdPolicy,
ProjectionArrayRecursionPolicy arrayRecursionPolicy,
ProjectionParseMode parseRules = ProjectionParseMode::kAllowComputedFields);
virtual ~ParsedAggregationProjection() = default;
/**
* Parse the user-specified BSON object 'spec'. By the time this is called, 'spec' has already
* been verified to not have any conflicting path specifications, and not to mix and match
* inclusions and exclusions. 'variablesParseState' is used by any contained expressions to
* track which variables are defined so that they can later be referenced at execution time.
*/
virtual void parse(const BSONObj& spec) = 0;
/**
* Optimize any expressions contained within this projection.
*/
virtual void optimize() {}
/**
* Add any dependencies needed by this projection or any sub-expressions to 'deps'.
*/
virtual DepsTracker::State addDependencies(DepsTracker* deps) const {
return DepsTracker::State::NOT_SUPPORTED;
}
/**
* Apply the projection transformation.
*/
Document applyTransformation(const Document& input) {
return applyProjection(input);
}
protected:
ParsedAggregationProjection(const boost::intrusive_ptr<ExpressionContext>& expCtx,
ProjectionDefaultIdPolicy defaultIdPolicy,
ProjectionArrayRecursionPolicy arrayRecursionPolicy)
: _expCtx(expCtx),
_arrayRecursionPolicy(arrayRecursionPolicy),
_defaultIdPolicy(defaultIdPolicy){};
/**
* Apply the projection to 'input'.
*/
virtual Document applyProjection(const Document& input) const = 0;
boost::intrusive_ptr<ExpressionContext> _expCtx;
ProjectionArrayRecursionPolicy _arrayRecursionPolicy;
ProjectionDefaultIdPolicy _defaultIdPolicy;
};
} // namespace parsed_aggregation_projection
} // namespace mongo
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