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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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 "mongo/db/exec/document_value/document_metadata_fields.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/pipeline/dependencies.h"
#include "mongo/db/pipeline/field_path.h"
#include "mongo/util/str.h"
namespace mongo {
std::list<std::string> DepsTracker::sortedFields() const {
// Use a special comparator to put parent fieldpaths before their children.
std::list<std::string> sortedFields(fields.begin(), fields.end());
sortedFields.sort(PathPrefixComparator());
return sortedFields;
}
BSONObj DepsTracker::toProjectionWithoutMetadata(
TruncateToRootLevel truncationBehavior /*= TruncateToRootLevel::no*/) const {
BSONObjBuilder bb;
if (needWholeDocument) {
return bb.obj();
}
if (fields.empty()) {
// We need no user-level fields (as we would if this was logically a count). Since there is
// no way of expressing a projection that indicates no depencies, we return an empty
// projection.
return bb.obj();
}
// Go through dependency fieldpaths to find the minimal set of projections that cover the
// dependencies. For example, the dependencies ["a.b", "a.b.c.g", "c", "c.d", "f"] would be
// minimally covered by the projection {"a.b": 1, "c": 1, "f": 1}. The key operation here is
// folding dependencies into ancestor dependencies, wherever possible. This is assisted by a
// special sort in DepsTracker::sortedFields that treats '.' as the first char and thus places
// parent paths directly before their children.
bool idSpecified = false;
std::string last;
for (const auto& field : sortedFields()) {
if (str::startsWith(field, "_id") && (field.size() == 3 || field[3] == '.')) {
idSpecified = true;
}
if (!last.empty() && str::startsWith(field, last)) {
// We are including a parent of this field, so we can skip this field.
continue;
}
// Check that the field requested is a valid field name in the agg language. This
// constructor will throw if it isn't.
FieldPath fp(field);
if (truncationBehavior == TruncateToRootLevel::yes) {
last = fp.front().toString() + '.';
bb.append(fp.front(), 1);
} else {
last = field + '.';
bb.append(field, 1);
}
}
if (!idSpecified) {
bb.append("_id", 0);
}
return bb.obj();
}
void DepsTracker::setNeedsMetadata(DocumentMetadataFields::MetaType type, bool required) {
uassert(40218,
str::stream() << "query requires " << type << " metadata, but it is not available",
!required || !_unavailableMetadata[type]);
// If the metadata type is not required, then it should not be recorded as a metadata
// dependency.
invariant(required || !_metadataDeps[type]);
_metadataDeps[type] = required;
}
// Returns true if the lhs value should sort before the rhs, false otherwise.
bool PathPrefixComparator::operator()(const std::string& lhs, const std::string& rhs) const {
constexpr char dot = '.';
for (size_t pos = 0, len = std::min(lhs.size(), rhs.size()); pos < len; ++pos) {
// Below, we explicitly choose unsigned char because the usual const char& returned by
// operator[] is actually signed on x86 and will incorrectly order unicode characters.
unsigned char 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();
}
} // namespace mongo
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