mongodb/jstests/sharding/agg_explain_fmt.js

// This test ensuexplain an explain of an aggregate through mongos has the intended format.
(function() {
    "use strict";

    load('jstests/libs/analyze_plan.js');  // For planHasStage.

    const st = new ShardingTest({shards: 2});
    const mongosDB = st.s.getDB("test");
    const coll = mongosDB.agg_explain_fmt;
    // Insert documents with {_id: -5} to {_id: 4}.
    assert.commandWorked(coll.insert(Array.from({length: 10}, (_, i) => ({_id: i - 5}))));

    // Test that with an unsharded collection we don't get any kind of 'splitPipeline', just the
    // normal explain with 'stages'.
    let explain = coll.explain().aggregate([{$project: {a: 1}}]);
    assert(!explain.hasOwnProperty("splitPipeline"), explain);
    assert(explain.hasOwnProperty("stages"), explain);

    // Now shard the collection by _id and move a chunk to each shard.
    st.shardColl(coll, {_id: 1}, {_id: 0}, {_id: 0});

    // Test that we now have a split pipeline with information about what pipeline ran on each
    // shard.
    explain = coll.explain().aggregate([{$project: {a: 1}}]);
    assert(explain.hasOwnProperty("splitPipeline"), explain);
    assert(explain.splitPipeline.hasOwnProperty("shardsPart"), explain.splitPipeline);
    assert(explain.splitPipeline.hasOwnProperty("mergerPart"), explain.splitPipeline);
    assert(explain.hasOwnProperty("shards"), explain);
    for (let shardId in explain.shards) {
        const shardExplain = explain.shards[shardId];
        assert(shardExplain.hasOwnProperty("host"), shardExplain);
        assert(shardExplain.hasOwnProperty("stages") || shardExplain.hasOwnProperty("queryPlanner"),
               shardExplain);
    }

    // Do a sharded explain from a mongod, not mongos, to ensure that it does not have a
    // SHARDING_FILTER stage.");
    const shardDB = st.shard0.getDB(mongosDB.getName());
    explain = shardDB[coll.getName()].explain().aggregate([{$match: {}}]);
    assert(!planHasStage(shardDB, explain.queryPlanner.winningPlan, "SHARDING_FILTER"), explain);
    st.stop();
}());