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// Tests that the aggregation pipeline correctly coalesces a $project stage at the front of the
// pipeline that can be covered by a normal query.
// @tags: [do_not_wrap_aggregations_in_facets]
(function() {
"use strict";
load("jstests/aggregation/extras/utils.js"); // For orderedArrayEq.
load('jstests/libs/analyze_plan.js'); // For planHasStage().
let coll = db.remove_redundant_projects;
coll.drop();
assert.writeOK(coll.insert({_id: {a: 1, b: 1}, a: 1, c: {d: 1}, e: ['elem1']}));
let indexSpec = {a: 1, 'c.d': 1, 'e.0': 1};
/**
* Helper to test that for a given pipeline, the same results are returned whether or not an
* index is present. Also tests whether a projection is absorbed by the pipeline
* ('expectProjectToCoalesce') and the corresponding project stage ('removedProjectStage') does
* not exist in the explain output.
*/
function assertResultsMatch({pipeline = [],
expectProjectToCoalesce = false,
removedProjectStage = null,
index = indexSpec,
pipelineOptimizedAway = false} = {}) {
// Add a match stage to ensure index scans are considered for planning (workaround for
// SERVER-20066).
pipeline = [{$match: {a: {$gte: 0}}}].concat(pipeline);
// Once with an index.
assert.commandWorked(coll.createIndex(index));
let explain = coll.explain().aggregate(pipeline);
let resultsWithIndex = coll.aggregate(pipeline).toArray();
// Projection does not get pushed down when sharding filter is used.
if (!explain.hasOwnProperty("shards")) {
let result;
if (pipelineOptimizedAway) {
assert(isQueryPlan(explain));
result = explain.queryPlanner.winningPlan;
} else {
assert(isAggregationPlan(explain));
result = explain.stages[0].$cursor.queryPlanner.winningPlan;
}
// Check that $project uses the query system.
assert.eq(expectProjectToCoalesce,
planHasStage(db, result, "PROJECTION_DEFAULT") ||
planHasStage(db, result, "PROJECTION_COVERED") ||
planHasStage(db, result, "PROJECTION_SIMPLE"));
if (!pipelineOptimizedAway) {
// Check that $project was removed from pipeline and pushed to the query system.
explain.stages.forEach(function(stage) {
if (stage.hasOwnProperty("$project"))
assert.neq(removedProjectStage, stage["$project"]);
});
}
}
// Again without an index.
assert.commandWorked(coll.dropIndex(index));
let resultsWithoutIndex = coll.aggregate(pipeline).toArray();
assert(orderedArrayEq(resultsWithIndex, resultsWithoutIndex));
}
// Test that covered projections correctly use the query system for projection and the $project
// stage is removed from the pipeline.
assertResultsMatch({
pipeline: [{$project: {_id: 0, a: 1}}],
expectProjectToCoalesce: true,
removedProjectStage: {_id: 0, a: 1},
pipelineOptimizedAway: true
});
assertResultsMatch({
pipeline: [{$project: {_id: 0, a: 1}}, {$group: {_id: null, a: {$sum: "$a"}}}],
expectProjectToCoalesce: true,
removedProjectStage: {_id: 0, a: 1}
});
assertResultsMatch({
pipeline: [{$sort: {a: -1}}, {$project: {_id: 0, a: 1}}],
expectProjectToCoalesce: true,
removedProjectStage: {_id: 0, a: 1},
pipelineOptimizedAway: true
});
assertResultsMatch({
pipeline: [
{$sort: {a: 1, 'c.d': 1}},
{$project: {_id: 0, a: 1}},
{$group: {_id: "$a", arr: {$push: "$a"}}}
],
expectProjectToCoalesce: true,
removedProjectStage: {_id: 0, a: 1}
});
assertResultsMatch({
pipeline: [{$project: {_id: 0, c: {d: 1}}}],
expectProjectToCoalesce: true,
removedProjectStage: {_id: 0, c: {d: 1}},
pipelineOptimizedAway: true
});
// Test that projections with renamed fields are not removed from the pipeline, however an
// inclusion projection is still pushed to the query system.
assertResultsMatch({pipeline: [{$project: {_id: 0, f: "$a"}}], expectProjectToCoalesce: true});
assertResultsMatch(
{pipeline: [{$project: {_id: 0, a: 1, f: "$a"}}], expectProjectToCoalesce: true});
// Test that uncovered projections include the $project stage in the pipeline.
assertResultsMatch(
{pipeline: [{$sort: {a: 1}}, {$project: {_id: 1, b: 1}}], expectProjectToCoalesce: false});
assertResultsMatch({
pipeline:
[{$sort: {a: 1}}, {$group: {_id: "$_id", arr: {$push: "$a"}}}, {$project: {arr: 1}}],
expectProjectToCoalesce: false
});
// Test that projections with computed fields are kept in the pipeline.
assertResultsMatch(
{pipeline: [{$project: {computedField: {$sum: "$a"}}}], expectProjectToCoalesce: false});
assertResultsMatch({pipeline: [{$project: {a: ["$a", "$b"]}}], expectProjectToCoalesce: false});
assertResultsMatch({
pipeline: [{
$project:
{e: {$filter: {input: "$e", as: "item", cond: {"$eq": ["$$item", "elem0"]}}}}
}],
expectProjectToCoalesce: false
});
// Test that only the first projection is removed from the pipeline.
assertResultsMatch({
pipeline: [
{$project: {_id: 0, a: 1}},
{$group: {_id: "$a", arr: {$push: "$a"}, a: {$sum: "$a"}}},
{$project: {_id: 0}}
],
expectProjectToCoalesce: true,
removedProjectStage: {_id: 0, a: 1}
});
// Test that projections on _id with nested fields are not removed from pipeline. Due to
// SERVER-7502, the dependency analysis does not generate a covered projection for nested
// fields in _id and thus we cannot remove the stage.
indexSpec = {'_id.a': 1, a: 1};
assertResultsMatch(
{pipeline: [{$project: {'_id.a': 1}}], expectProjectToCoalesce: false, index: indexSpec});
}());
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