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/**
* Copyright (C) 2019-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.
*/
#pragma once
#include "mongo/db/exec/document_value/document.h"
#include "mongo/db/exec/projection_executor.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/pipeline/field_path.h"
namespace mongo::projection_executor_utils {
/**
* Applies the projection to a single field name. Returns whether or not the projection would
* allow that field to remain in a document.
**/
bool applyProjectionToOneField(projection_executor::ProjectionExecutor* executor, StringData field);
/**
* Applies the projection to each field from the 'fields' set and stores it in the returned set
* if the projection would allow that field to remain in a document.
**/
template <typename Container>
stdx::unordered_set<std::string> applyProjectionToFields(
projection_executor::ProjectionExecutor* executor, Container const& fields) {
stdx::unordered_set<std::string> out;
for (const auto& field : fields) {
if (applyProjectionToOneField(executor, field)) {
out.insert(field);
}
}
return out;
}
/**
* Applies a positional projection on the first array found in the 'path' on a projection
* 'preImage' document. The applied projection is merged with a projection 'postImage' document.
* The 'matchExpr' specifies a condition to locate the first matching element in the array and must
* match the input document. Note that the match expression must be applied to the projection
* post-image, as it may contain conditions on fields which are not included into the projection
* post-image. So, the pre-image document will be used to match an array and record a position of
* the matching element, whilst the actual result will be merged into the post-image.
*
* For example, given:
*
* - the 'preImage' document {bar: 1, foo: {bar: [1,2,6,10]}}
* - the 'postImage' document {foo: {bar: [1,2,6,10]}}
* - the 'matchExpr' condition {bar: 1, 'foo.bar': {$gte: 5}}
* - and the 'path' for the positional projection of 'foo.bar'
*
* The resulting document will contain the following element: {foo: {bar: [6]}}
*
* Throws an AssertionException if 'matchExpr' matches the input document, but an array element
* satisfying positional projection requirements cannot be found.
*/
Document applyFindPositionalProjection(const Document& preImage,
const Document& postImage,
const MatchExpression& matchExpr,
const FieldPath& path);
/**
* Applies an $elemMatch projection on the array at the given 'path' on the 'input' document. The
* applied projection is stored in the output Value. The 'matchExpr' specifies a condition to
* locate the first matching element in the array and must contain the $elemMatch operator. This
* function doesn't enforce this requirement and the caller must ensure that the valid match
* expression is passed. For example, given:
*
* - the 'input' document {foo: [{bar: 1}, {bar: 2}, {bar: 3}]}
* - the 'matchExpr' condition {foo: {$elemMatch: {bar: {$gt: 1}}}}
* - and the 'path' of 'foo'
*
* The resulting value will be: [{bar: 2}]
*
* If the 'matchExpr' does not match the input document, the function returns a missing value.
*
* Since the $elemMatch projection cannot be used with a nested field, the 'path' value must not
* be a dotted path, otherwise a tassert will be triggered.
*/
Value applyFindElemMatchProjection(const Document& input,
const MatchExpression& matchExpr,
const FieldPath& path);
/**
* Applies a $slice projection on the array at the given 'path' on the 'input' document. The applied
* projection is returned as a Document. The 'skip' parameter indicates the number of items in the
* array to skip and the 'limit' indicates the number of items to return.
*
* If any of the 'skip' or 'limit' is negative, it is applied to the last items in the array (e.g.,
* {$slice: -5} returns the last five items in array, and {$slice: [-20, 10]} returns 10 items,
* beginning with the item that is 20th from the last item of the array.
*
* If the 'skip' is specified, the 'limit' cannot be negative.
*
* For example, given:
*
* - the 'input' document {foo: [{bar: 1}, {bar: 2}, {bar: 3}, {bar: 4}]}
* - the path of 'foo'
* - the 'skip' of -3 and 'limit' of 2
*
* The resulting document will contain the following element: {foo: [{bar: 2}, {bar: 3}]}.
*/
Document applyFindSliceProjection(const Document& input,
const FieldPath& path,
boost::optional<int> skip,
int limit);
} // namespace mongo::projection_executor_utils
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