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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.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/exec/projection_executor_builder.h"
#include "mongo/base/exact_cast.h"
#include "mongo/db/exec/exclusion_projection_executor.h"
#include "mongo/db/exec/inclusion_projection_executor.h"
#include "mongo/db/pipeline/expression_find_internal.h"
#include "mongo/db/query/projection_ast_path_tracking_visitor.h"
#include "mongo/db/query/tree_walker.h"
#include "mongo/db/query/util/make_data_structure.h"
namespace mongo::projection_executor {
namespace {
constexpr auto kInclusion = projection_ast::ProjectType::kInclusion;
constexpr auto kExclusion = projection_ast::ProjectType::kExclusion;
constexpr auto kProjectionPostImageVarName = ProjectionExecutor::kProjectionPostImageVarName;
/**
* Holds data used to built a projection executor while walking an AST tree. This struct is attached
* to 'PathTrackingVisitorContext' and can be accessed by projection AST visitors to track the
* current context.
*/
template <typename Executor>
struct ProjectionExecutorVisitorData {
// A projection executor returned upon completion of AST traversal.
std::unique_ptr<Executor> executor;
boost::intrusive_ptr<ExpressionContext> expCtx;
// A root replacement expression to be attached to the projection executor, if any. If there
// are multiple root replacement expressions in the AST, they will be chained together, so that
// one expression becomes an input to another.
boost::intrusive_ptr<Expression> rootReplacementExpression;
auto rootNode() const {
return executor->getRoot();
}
void setRootReplacementExpression(boost::intrusive_ptr<Expression> expr) {
rootReplacementExpression = expr;
executor->setRootReplacementExpression(rootReplacementExpression);
}
};
template <typename Executor>
using ProjectionExecutorVisitorContext =
projection_ast::PathTrackingVisitorContext<ProjectionExecutorVisitorData<Executor>>;
template <typename Executor>
auto makeProjectionPreImageExpression(const ProjectionExecutorVisitorData<Executor>& data) {
return ExpressionFieldPath::parse(
data.expCtx.get(), "$$ROOT", data.expCtx->variablesParseState);
}
template <typename Executor>
auto makeProjectionPostImageExpression(const ProjectionExecutorVisitorData<Executor>& data) {
return data.rootReplacementExpression
? data.rootReplacementExpression
: ExpressionFieldPath::parse(data.expCtx.get(),
"$$" + kProjectionPostImageVarName,
data.expCtx->variablesParseState);
}
/**
* Creates a find()-style positional expression from the given AST 'node' to be applied to the
* 'path' on the input document. If the visitor 'data' already contains a root replacement
* expression, it will be used as an input operand to the new root replacement expression, otherwise
* a field path expressions will be created to access a projection post-image document.
*/
template <typename Executor>
auto createFindPositionalExpression(const projection_ast::ProjectionPositionalASTNode* node,
const ProjectionExecutorVisitorData<Executor>& data,
const FieldPath& path) {
invariant(node);
const auto& children = node->children();
invariant(children.size() == 1UL);
auto matchExprNode =
exact_pointer_cast<projection_ast::MatchExpressionASTNode*>(children[0].get());
invariant(matchExprNode);
return make_intrusive<ExpressionInternalFindPositional>(data.expCtx.get(),
makeProjectionPreImageExpression(data),
makeProjectionPostImageExpression(data),
path,
matchExprNode->matchExpression());
}
/**
* Creates a find()-style $slice expression from the given AST 'node' to be applied to the
* 'path' on the input document. If the visitor 'data' already contains a root replacement
* expression, it will be used as an input operand to the new root replacement expression, otherwise
* a field path expressions will be created to access a projection post-image document.
*/
template <typename Executor>
auto createFindSliceExpression(const projection_ast::ProjectionSliceASTNode* node,
const ProjectionExecutorVisitorData<Executor>& data,
const FieldPath& path) {
invariant(node);
return make_intrusive<ExpressionInternalFindSlice>(data.expCtx.get(),
makeProjectionPostImageExpression(data),
path,
node->skip(),
node->limit());
}
/**
* Creates a find()-style $elemMatch expression from the given AST 'node' to be applied at the
* 'path' on the input document.
*/
template <typename Executor>
auto createFindElemMatchExpression(const projection_ast::ProjectionElemMatchASTNode* node,
const ProjectionExecutorVisitorData<Executor>& data,
const FieldPath& path) {
invariant(node);
const auto& children = node->children();
invariant(children.size() == 1UL);
auto matchExprNode =
exact_pointer_cast<projection_ast::MatchExpressionASTNode*>(children[0].get());
invariant(matchExprNode);
return make_intrusive<ExpressionInternalFindElemMatch>(data.expCtx.get(),
makeProjectionPreImageExpression(data),
path,
matchExprNode->matchExpression());
}
/**
* A projection AST visitor which creates inclusion or exclusion nodes in the projection execution
* tree by calling corresponding 'addProjectionForPath()' or 'addExpressionForPath()' on the root
* node of the tree while traversing the AST. If the AST contains root-replacement expressions, they
* will be attached to the projection executor.
*
* To track the current path in the projection, this visitor should be used with
* 'PathTrackingWalker' which will help to maintain the current path via
* 'PathTrackingVisitorContext'.
*/
template <typename Executor>
class ProjectionExecutorVisitor final : public projection_ast::ProjectionASTConstVisitor {
public:
ProjectionExecutorVisitor(ProjectionExecutorVisitorContext<Executor>* context)
: _context{context} {
invariant(_context);
}
void visit(const projection_ast::ProjectionPositionalASTNode* node) final {
constexpr auto isInclusion = std::is_same_v<Executor, InclusionProjectionExecutor>;
invariant(isInclusion);
const auto& path = _context->fullPath();
auto& userData = _context->data();
userData.rootNode()->addProjectionForPath(path.fullPath());
userData.setRootReplacementExpression(createFindPositionalExpression(node, userData, path));
}
void visit(const projection_ast::ProjectionSliceASTNode* node) final {
const auto& path = _context->fullPath();
auto& userData = _context->data();
// A $slice expression can be applied to an exclusion projection. In this case we don't need
// to project out the path to which $slice is applied, since it will already be included
// into the output document.
if constexpr (std::is_same_v<Executor, InclusionProjectionExecutor>) {
userData.rootNode()->addProjectionForPath(path.fullPath());
}
userData.setRootReplacementExpression(createFindSliceExpression(node, userData, path));
}
void visit(const projection_ast::ProjectionElemMatchASTNode* node) final {
const auto& path = _context->fullPath();
const auto& userData = _context->data();
userData.rootNode()->addExpressionForPath(
path.fullPath(), createFindElemMatchExpression(node, userData, path));
}
void visit(const projection_ast::ExpressionASTNode* node) final {
const auto& path = _context->fullPath();
const auto& userData = _context->data();
userData.rootNode()->addExpressionForPath(path.fullPath(), node->expression());
}
void visit(const projection_ast::BooleanConstantASTNode* node) final {
const auto& path = _context->fullPath();
const auto& userData = _context->data();
// In an inclusion projection only the _id field can be excluded from the result document.
// If this is the case, then we don't need to include the field into the projection.
if constexpr (std::is_same_v<Executor, InclusionProjectionExecutor>) {
const auto isIdField = path == "_id";
if (isIdField && !node->value()) {
return;
}
// In inclusion projection only _id field can be excluded, make sure this is the case.
invariant(!isIdField || node->value());
}
userData.rootNode()->addProjectionForPath(path.fullPath());
}
void visit(const projection_ast::ProjectionPathASTNode* node) final {}
void visit(const projection_ast::MatchExpressionASTNode* node) final {}
private:
ProjectionExecutorVisitorContext<Executor>* _context;
};
/**
* A helper function which creates a 'ProjectionExecutorWalker' to walk a projection AST,
* starting at the node 'root', and build a projection executor of the specified type
* 'Executor'.
*/
template <typename Executor>
auto buildProjectionExecutor(boost::intrusive_ptr<ExpressionContext> expCtx,
const projection_ast::ProjectionPathASTNode* root,
const ProjectionPolicies policies,
const BuilderParamsBitSet params) {
ProjectionExecutorVisitorContext<Executor> context{
{std::make_unique<Executor>(expCtx, policies, params[kAllowFastPath]), expCtx}};
ProjectionExecutorVisitor<Executor> executorVisitor{&context};
projection_ast::PathTrackingWalker walker{&context, {&executorVisitor}, {}};
tree_walker::walk<true, projection_ast::ASTNode>(root, &walker);
if (params[kOptimizeExecutor]) {
context.data().executor->optimize();
}
return std::move(context.data().executor);
}
} // namespace
std::unique_ptr<ProjectionExecutor> buildProjectionExecutor(
boost::intrusive_ptr<ExpressionContext> expCtx,
const projection_ast::Projection* projection,
const ProjectionPolicies policies,
BuilderParamsBitSet params) {
invariant(projection);
// Fast-path can only be used with inclusion-only projections, so we need to reset the
// fast-path flag.
if (!projection->isInclusionOnly()) {
params.reset(kAllowFastPath);
}
switch (projection->type()) {
case kInclusion:
return buildProjectionExecutor<InclusionProjectionExecutor>(
expCtx, projection->root(), policies, params);
case kExclusion:
return buildProjectionExecutor<ExclusionProjectionExecutor>(
expCtx, projection->root(), policies, params);
default:
MONGO_UNREACHABLE;
}
}
} // namespace mongo::projection_executor
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