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/**
* Copyright (C) 2020-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/query/sbe_stage_builder_projection.h"
#include "mongo/db/exec/sbe/stages/co_scan.h"
#include "mongo/db/exec/sbe/stages/filter.h"
#include "mongo/db/exec/sbe/stages/limit_skip.h"
#include "mongo/db/exec/sbe/stages/makeobj.h"
#include "mongo/db/exec/sbe/stages/project.h"
#include "mongo/db/exec/sbe/stages/traverse.h"
#include "mongo/db/exec/sbe/values/bson.h"
#include "mongo/db/query/sbe_stage_builder_expression.h"
#include "mongo/db/query/tree_walker.h"
#include "mongo/util/str.h"
#include "mongo/util/visit_helper.h"
namespace mongo::stage_builder {
namespace {
using ExpressionType = std::unique_ptr<sbe::EExpression>;
using PlanStageType = std::unique_ptr<sbe::PlanStage>;
/**
* Stores context across calls to visit() in the projection traversal visitors.
*/
struct ProjectionTraversalVisitorContext {
// Stores the field names to visit at each nested projection level, and the base path to this
// level. Top of the stack is the most recently visited level.
struct NestedLevel {
// The input slot for the current level. This is the parent sub-document for each of the
// projected fields at the current level.
sbe::value::SlotId inputSlot;
// The fields names at the current projection level.
std::list<std::string> fields;
// All but the last path component of the current path being visited. None if at the
// top-level and there is no "parent" path.
std::stack<std::string> basePath;
// A traversal sub-tree which combines traversals for each of the fields at the current
// level.
PlanStageType fieldPathExpressionsTraverseStage{
sbe::makeS<sbe::LimitSkipStage>(sbe::makeS<sbe::CoScanStage>(), 1, boost::none)};
};
// Stores evaluation expressions for each of the projections at the current nested level. It can
// evaluate either to an expression, if we're at the leaf node of the projection, or a sub-tree,
// if we're evaluating a field projection in the middle of the path. The stack elements are
// optional because for an exclusion projection we don't need to evaluate anything, but we need
// to have an element on the stack which corresponds to a projected field.
struct ProjectEval {
sbe::value::SlotId inputSlot;
sbe::value::SlotId outputSlot;
stdx::variant<PlanStageType, ExpressionType> expr;
};
const auto& topFrontField() const {
invariant(!levels.empty());
invariant(!levels.top().fields.empty());
return levels.top().fields.front();
}
void popFrontField() {
invariant(!levels.empty());
invariant(!levels.top().fields.empty());
levels.top().fields.pop_front();
}
auto& topLevel() {
invariant(!levels.empty());
return levels.top();
}
void popLevel() {
invariant(!levels.empty());
invariant(levels.top().fields.empty());
levels.pop();
}
void pushLevel(std::list<std::string> fields) {
levels.push({levels.empty() ? inputSlot : slotIdGenerator->generate(), std::move(fields)});
}
std::pair<sbe::value::SlotId, PlanStageType> done() {
invariant(evals.size() == 1);
auto eval = std::move(evals.top());
invariant(eval);
invariant(stdx::holds_alternative<PlanStageType>(eval->expr));
return {eval->outputSlot,
sbe::makeS<sbe::TraverseStage>(std::move(inputStage),
std::move(stdx::get<PlanStageType>(eval->expr)),
eval->inputSlot,
eval->outputSlot,
eval->outputSlot,
sbe::makeSV(),
nullptr,
nullptr)};
}
projection_ast::ProjectType projectType;
sbe::value::SlotIdGenerator* const slotIdGenerator;
sbe::value::FrameIdGenerator* const frameIdGenerator;
// The input stage to this projection and the slot to read a root document from.
PlanStageType inputStage;
sbe::value::SlotId inputSlot;
std::stack<NestedLevel> levels;
std::stack<boost::optional<ProjectEval>> evals;
// See the comment above the generateExpression() declaration for an explanation of the
// 'relevantSlots' list.
sbe::value::SlotVector relevantSlots;
};
/**
* A projection traversal pre-visitor used for maintaining nested levels while traversing a
* projection AST.
*/
class ProjectionTraversalPreVisitor final : public projection_ast::ProjectionASTConstVisitor {
public:
ProjectionTraversalPreVisitor(ProjectionTraversalVisitorContext* context) : _context{context} {
invariant(_context);
}
void visit(const projection_ast::ProjectionPathASTNode* node) final {
if (node->parent()) {
_context->topLevel().basePath.push(_context->topFrontField());
_context->popFrontField();
}
_context->pushLevel({node->fieldNames().begin(), node->fieldNames().end()});
}
void visit(const projection_ast::ProjectionPositionalASTNode* node) final {
uasserted(4822885, str::stream() << "Positional projection is not supported in SBE");
}
void visit(const projection_ast::ProjectionSliceASTNode* node) final {
uasserted(4822886, str::stream() << "Slice projection is not supported in SBE");
}
void visit(const projection_ast::ProjectionElemMatchASTNode* node) final {
uasserted(4822887, str::stream() << "ElemMatch projection is not supported in SBE");
}
void visit(const projection_ast::ExpressionASTNode* node) final {}
void visit(const projection_ast::MatchExpressionASTNode* node) final {
uasserted(4822888,
str::stream() << "Projection match expressions are not supported in SBE");
}
void visit(const projection_ast::BooleanConstantASTNode* node) final {}
private:
ProjectionTraversalVisitorContext* _context;
};
/**
* A projection traversal post-visitor used for maintaining nested levels while traversing a
* projection AST and producing an SBE traversal sub-tree for each nested level.
*/
class ProjectionTraversalPostVisitor final : public projection_ast::ProjectionASTConstVisitor {
public:
ProjectionTraversalPostVisitor(ProjectionTraversalVisitorContext* context) : _context{context} {
invariant(_context);
}
void visit(const projection_ast::BooleanConstantASTNode* node) final {
using namespace std::literals;
// If this is an inclusion projection, extract the field and push a getField expression on
// top of the 'evals' stack. For an exclusion projection just push an empty optional.
if (node->value()) {
_context->evals.push(
{{_context->topLevel().inputSlot,
_context->slotIdGenerator->generate(),
sbe::makeE<sbe::EFunction>(
"getField"sv,
sbe::makeEs(sbe::makeE<sbe::EVariable>(_context->topLevel().inputSlot),
sbe::makeE<sbe::EConstant>(_context->topFrontField())))}});
} else {
_context->evals.push({});
}
_context->popFrontField();
}
void visit(const projection_ast::ExpressionASTNode* node) final {
// Generate an expression to evaluate a projection expression and push it on top of the
// 'evals' stack. If the expression is translated into a sub-tree, stack it with the
// existing 'fieldPathExpressionsTraverseStage' sub-tree.
auto [outputSlot, expr, stage] =
generateExpression(node->expressionRaw(),
std::move(_context->topLevel().fieldPathExpressionsTraverseStage),
_context->slotIdGenerator,
_context->frameIdGenerator,
_context->inputSlot,
&_context->relevantSlots);
_context->evals.push({{_context->topLevel().inputSlot, outputSlot, std::move(expr)}});
_context->topLevel().fieldPathExpressionsTraverseStage = std::move(stage);
_context->popFrontField();
}
void visit(const projection_ast::ProjectionPathASTNode* node) final {
using namespace std::literals;
const auto isInclusion = _context->projectType == projection_ast::ProjectType::kInclusion;
sbe::value::SlotMap<std::unique_ptr<sbe::EExpression>> projects;
sbe::value::SlotVector projectSlots;
std::vector<std::string> projectFields;
std::vector<std::string> restrictFields;
auto inputStage{std::move(_context->topLevel().fieldPathExpressionsTraverseStage)};
invariant(_context->evals.size() >= node->fieldNames().size());
// Walk through all the fields at the current nested level in reverse order (to match field
// names with the elements on the 'evals' stack) and,
// * For exclusion projections populate the 'restrictFields' array to be passed to the
// mkobj stage below, which constructs an output document for the current nested level.
// * For inclusion projections,
// - Populates 'projectFields' and 'projectSlots' vectors holding field names to
// project, and slots to access evaluated projection values.
// - Populates 'projects' map to actually project out the values.
// - For nested paths injects a traversal sub-tree.
for (auto it = node->fieldNames().rbegin(); it != node->fieldNames().rend(); ++it) {
auto eval = std::move(_context->evals.top());
_context->evals.pop();
// If the projection eval element is empty, then this is an exclusion projection and we
// can put the field name to the vector of restricted fields.
if (!eval) {
restrictFields.push_back(*it);
continue;
}
projectSlots.push_back(eval->outputSlot);
projectFields.push_back(*it);
stdx::visit(
visit_helper::Overloaded{
[&](ExpressionType& expr) {
projects.emplace(eval->outputSlot, std::move(expr));
},
[&](PlanStageType& stage) {
invariant(!_context->topLevel().basePath.empty());
inputStage = sbe::makeProjectStage(
std::move(inputStage),
eval->inputSlot,
sbe::makeE<sbe::EFunction>(
"getField"sv,
sbe::makeEs(
sbe::makeE<sbe::EVariable>(_context->topLevel().inputSlot),
sbe::makeE<sbe::EConstant>(
_context->topLevel().basePath.top()))));
_context->topLevel().basePath.pop();
inputStage = sbe::makeS<sbe::TraverseStage>(std::move(inputStage),
std::move(stage),
eval->inputSlot,
eval->outputSlot,
eval->outputSlot,
sbe::makeSV(),
nullptr,
nullptr);
}},
eval->expr);
}
// We walked through the field names in reverse order, so need to reverse the following two
// vectors.
std::reverse(projectFields.begin(), projectFields.end());
std::reverse(projectSlots.begin(), projectSlots.end());
// If we have something to actually project, then inject a projection stage.
if (!projects.empty()) {
inputStage = sbe::makeS<sbe::ProjectStage>(std::move(inputStage), std::move(projects));
}
// Finally, inject an mkobj stage to generate a document for the current nested level. For
// inclusion projection also add constant filter stage on top to filter out input values for
// nested traversal if they're not documents.
auto outputSlot = _context->slotIdGenerator->generate();
_context->relevantSlots.push_back(outputSlot);
_context->evals.push(
{{_context->topLevel().inputSlot,
outputSlot,
isInclusion ? sbe::makeS<sbe::FilterStage<true>>(
sbe::makeS<sbe::MakeObjStage>(std::move(inputStage),
outputSlot,
boost::none,
std::vector<std::string>{},
std::move(projectFields),
std::move(projectSlots),
true,
false),
sbe::makeE<sbe::EFunction>("isObject"sv,
sbe::makeEs(sbe::makeE<sbe::EVariable>(
_context->topLevel().inputSlot))))
: sbe::makeS<sbe::MakeObjStage>(std::move(inputStage),
outputSlot,
_context->topLevel().inputSlot,
std::move(restrictFields),
std::move(projectFields),
std::move(projectSlots),
false,
true)}});
// We've done with the current nested level.
_context->popLevel();
}
void visit(const projection_ast::ProjectionPositionalASTNode* node) final {}
void visit(const projection_ast::ProjectionSliceASTNode* node) final {}
void visit(const projection_ast::ProjectionElemMatchASTNode* node) final {}
void visit(const projection_ast::MatchExpressionASTNode* node) final {}
private:
ProjectionTraversalVisitorContext* _context;
};
class ProjectionTraversalWalker final {
public:
ProjectionTraversalWalker(projection_ast::ProjectionASTConstVisitor* preVisitor,
projection_ast::ProjectionASTConstVisitor* postVisitor)
: _preVisitor{preVisitor}, _postVisitor{postVisitor} {}
void preVisit(const projection_ast::ASTNode* node) {
node->acceptVisitor(_preVisitor);
}
void postVisit(const projection_ast::ASTNode* node) {
node->acceptVisitor(_postVisitor);
}
void inVisit(long count, const projection_ast::ASTNode* node) {}
private:
projection_ast::ProjectionASTConstVisitor* _preVisitor;
projection_ast::ProjectionASTConstVisitor* _postVisitor;
};
} // namespace
std::pair<sbe::value::SlotId, PlanStageType> generateProjection(
const projection_ast::Projection* projection,
PlanStageType stage,
sbe::value::SlotIdGenerator* slotIdGenerator,
sbe::value::FrameIdGenerator* frameIdGenerator,
sbe::value::SlotId inputVar) {
ProjectionTraversalVisitorContext context{
projection->type(), slotIdGenerator, frameIdGenerator, std::move(stage), inputVar};
context.relevantSlots.push_back(inputVar);
ProjectionTraversalPreVisitor preVisitor{&context};
ProjectionTraversalPostVisitor postVisitor{&context};
ProjectionTraversalWalker walker{&preVisitor, &postVisitor};
tree_walker::walk<true, projection_ast::ASTNode>(projection->root(), &walker);
return context.done();
}
} // namespace mongo::stage_builder
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