db/ops/modifier_compare.cpp

/**
 *    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.
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 *    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>.
 *
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 *    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)
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#include "mongo/db/ops/modifier_compare.h"

#include "mongo/base/error_codes.h"
#include "mongo/bson/mutable/document.h"
#include "mongo/db/query/collation/collator_interface.h"
#include "mongo/db/update/field_checker.h"
#include "mongo/db/update/log_builder.h"
#include "mongo/db/update/path_support.h"
#include "mongo/util/mongoutils/str.h"

namespace mongo {

namespace str = mongoutils::str;

struct ModifierCompare::PreparedState {
    PreparedState(mutablebson::Document& targetDoc)
        : doc(targetDoc), idxFound(0), elemFound(doc.end()) {}

    // Document that is going to be changed.
    mutablebson::Document& doc;

    // Index in _fieldRef for which an Element exist in the document.
    size_t idxFound;

    // Element corresponding to _fieldRef[0.._idxFound].
    mutablebson::Element elemFound;
};

ModifierCompare::ModifierCompare(ModifierCompare::ModifierCompareMode mode)
    : _mode(mode), _pathReplacementPosition(0) {}

ModifierCompare::~ModifierCompare() {}

Status ModifierCompare::init(const BSONElement& modExpr, const Options& opts, bool* positional) {
    _updatePath.parse(modExpr.fieldName());
    Status status = fieldchecker::isUpdatable(_updatePath);
    if (!status.isOK()) {
        return status;
    }

    // If a $-positional operator was used, get the index in which it occurred
    // and ensure only one occurrence.
    size_t foundCount;
    bool foundDollar =
        fieldchecker::isPositional(_updatePath, &_pathReplacementPosition, &foundCount);

    if (positional)
        *positional = foundDollar;

    if (foundDollar && foundCount > 1) {
        return Status(ErrorCodes::BadValue,
                      str::stream() << "Too many positional (i.e. '$') elements found in path '"
                                    << _updatePath.dottedField()
                                    << "'");
    }

    // Store value for later.
    _val = modExpr;
    _collator = opts.expCtx->getCollator();
    return Status::OK();
}

Status ModifierCompare::prepare(mutablebson::Element root,
                                StringData matchedField,
                                ExecInfo* execInfo) {
    _preparedState.reset(new PreparedState(root.getDocument()));

    // If we have a $-positional field, it is time to bind it to an actual field part.
    if (_pathReplacementPosition) {
        if (matchedField.empty()) {
            return Status(ErrorCodes::BadValue,
                          str::stream() << "The positional operator did not find the match "
                                           "needed from the query. Unexpanded update: "
                                        << _updatePath.dottedField());
        }
        _updatePath.setPart(_pathReplacementPosition, matchedField);
    }

    // Locate the field name in 'root'. Note that we may not have all the parts in the path
    // in the doc -- which is fine. Our goal now is merely to reason about whether this mod
    // apply is a noOp or whether is can be in place. The remaining path, if missing, will
    // be created during the apply.
    Status status = pathsupport::findLongestPrefix(
        _updatePath, root, &_preparedState->idxFound, &_preparedState->elemFound);
    const auto elemFoundIsArray =
        _preparedState->elemFound.ok() && _preparedState->elemFound.getType() == BSONType::Array;

    // FindLongestPrefix may say the path does not exist at all, which is fine here, or
    // that the path was not viable or otherwise wrong, in which case, the mod cannot
    // proceed.
    if (status.code() == ErrorCodes::NonExistentPath) {
        _preparedState->elemFound = root.getDocument().end();
    } else if (!status.isOK()) {
        return status;
    }

    // We register interest in the field name. The driver needs this info to sort out if
    // there is any conflict among mods.
    execInfo->fieldRef[0] = &_updatePath;

    const bool destExists = (_preparedState->elemFound.ok() &&
                             _preparedState->idxFound == (_updatePath.numParts() - 1));
    if (!destExists) {
        execInfo->noOp = false;

        if (elemFoundIsArray) {
            // Report that an existing array will gain a new element as a result of this mod.
            execInfo->indexOfArrayWithNewElement[0] = _preparedState->idxFound;
        }
    } else {
        const int compareVal =
            _preparedState->elemFound.compareWithBSONElement(_val, _collator, false);
        execInfo->noOp = (compareVal == 0) ||
            ((_mode == ModifierCompare::MAX) ? (compareVal > 0) : (compareVal < 0));
    }

    return Status::OK();
}

Status ModifierCompare::apply() const {
    const bool destExists = (_preparedState->elemFound.ok() &&
                             _preparedState->idxFound == (_updatePath.numParts() - 1));
    // If there's no need to create any further field part, the $set is simply a value
    // assignment.
    if (destExists) {
        return _preparedState->elemFound.setValueBSONElement(_val);
    }

    mutablebson::Document& doc = _preparedState->doc;
    StringData lastPart = _updatePath.getPart(_updatePath.numParts() - 1);
    // If the element exists and is the same type, then that is what we want to work with
    mutablebson::Element elemToSet = doc.makeElementWithNewFieldName(lastPart, _val);
    if (!elemToSet.ok()) {
        return Status(ErrorCodes::InternalError, "can't create new element");
    }

    // Now, we can be in two cases here, as far as attaching the element being set goes:
    // (a) none of the parts in the element's path exist, or (b) some parts of the path
    // exist but not all.
    if (!_preparedState->elemFound.ok()) {
        _preparedState->elemFound = doc.root();
        _preparedState->idxFound = 0;
    } else {
        _preparedState->idxFound++;
    }

    // createPathAt() will complete the path and attach 'elemToSet' at the end of it.
    return pathsupport::createPathAt(
               _updatePath, _preparedState->idxFound, _preparedState->elemFound, elemToSet)
        .getStatus();
}

Status ModifierCompare::log(LogBuilder* logBuilder) const {
    return logBuilder->addToSetsWithNewFieldName(_updatePath.dottedField(), _val);
}

}  // namespace mongo