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/**
* Copyright 2011 (c) 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.
*/
#define MONGO_PCH_WHITELISTED
#include "mongo/platform/basic.h"
#include "mongo/pch.h"
#undef MONGO_PCH_WHITELISTED
#include "mongo/db/jsobj.h"
#include "mongo/db/pipeline/document.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/value.h"
namespace mongo {
/** Helper class to unwind array from a single document. */
class DocumentSourceUnwind::Unwinder {
public:
/** @param unwindPath is the field path to the array to unwind. */
Unwinder(const FieldPath& unwindPath);
/** Reset the unwinder to unwind a new document. */
void resetDocument(const Document& document);
/**
* @return the next document unwound from the document provided to resetDocument(), using
* the current value in the array located at the provided unwindPath.
*
* Returns boost::none if the array is exhausted.
*/
boost::optional<Document> getNext();
private:
// Path to the array to unwind.
const FieldPath _unwindPath;
Value _inputArray;
MutableDocument _output;
// Document indexes of the field path components.
vector<Position> _unwindPathFieldIndexes;
// Index into the _inputArray to return next.
size_t _index;
};
DocumentSourceUnwind::Unwinder::Unwinder(const FieldPath& unwindPath):
_unwindPath(unwindPath) {
}
void DocumentSourceUnwind::Unwinder::resetDocument(const Document& document) {
// Reset document specific attributes.
_inputArray = Value();
_output.reset(document);
_unwindPathFieldIndexes.clear();
_index = 0;
Value pathValue = document.getNestedField(_unwindPath, &_unwindPathFieldIndexes);
if (pathValue.nullish()) {
// The path does not exist or is null.
return;
}
// The target field must be an array to unwind.
uassert(15978, str::stream() << "Value at end of $unwind field path '"
<< _unwindPath.getPath(true) << "' must be an Array, but is a "
<< typeName(pathValue.getType()),
pathValue.getType() == Array);
_inputArray = pathValue;
}
boost::optional<Document> DocumentSourceUnwind::Unwinder::getNext() {
if (_inputArray.missing() || _index == _inputArray.getArrayLength())
return boost::none;
// If needed, this will automatically clone all the documents along the
// field path so that the end values are not shared across documents
// that have come out of this pipeline operator. This is a partial deep
// clone. Because the value at the end will be replaced, everything
// along the path leading to that will be replaced in order not to share
// that change with any other clones (or the original).
_output.setNestedField(_unwindPathFieldIndexes, _inputArray[_index]);
_index++;
return _output.peek();
}
const char DocumentSourceUnwind::unwindName[] = "$unwind";
DocumentSourceUnwind::DocumentSourceUnwind(
const intrusive_ptr<ExpressionContext> &pExpCtx):
DocumentSource(pExpCtx) {
}
const char *DocumentSourceUnwind::getSourceName() const {
return unwindName;
}
boost::optional<Document> DocumentSourceUnwind::getNext() {
pExpCtx->checkForInterrupt();
boost::optional<Document> out = _unwinder->getNext();
while (!out) {
// No more elements in array currently being unwound. This will loop if the input
// document is missing the unwind field or has an empty array.
boost::optional<Document> input = pSource->getNext();
if (!input)
return boost::none; // input exhausted
// Try to extract an output document from the new input document.
_unwinder->resetDocument(*input);
out = _unwinder->getNext();
}
return out;
}
Value DocumentSourceUnwind::serialize(bool explain) const {
verify(_unwindPath);
return Value(DOC(getSourceName() << _unwindPath->getPath(true)));
}
DocumentSource::GetDepsReturn DocumentSourceUnwind::getDependencies(DepsTracker* deps) const {
deps->fields.insert(_unwindPath->getPath(false));
return SEE_NEXT;
}
void DocumentSourceUnwind::unwindPath(const FieldPath &fieldPath) {
// Can't set more than one unwind path.
uassert(15979, str::stream() << unwindName << "can't unwind more than one path",
!_unwindPath);
// Record the unwind path.
_unwindPath.reset(new FieldPath(fieldPath));
_unwinder.reset(new Unwinder(fieldPath));
}
intrusive_ptr<DocumentSource> DocumentSourceUnwind::createFromBson(
BSONElement elem,
const intrusive_ptr<ExpressionContext> &pExpCtx) {
/*
The value of $unwind should just be a field path.
*/
uassert(15981, str::stream() << "the " << unwindName <<
" field path must be specified as a string",
elem.type() == String);
string prefixedPathString(elem.str());
string pathString(Expression::removeFieldPrefix(prefixedPathString));
intrusive_ptr<DocumentSourceUnwind> pUnwind(new DocumentSourceUnwind(pExpCtx));
pUnwind->unwindPath(FieldPath(pathString));
return pUnwind;
}
}
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