mongodb/jstests/sharding/empty_doc_results.js

// Verifies that mongos correctly handles empty documents when all fields are projected out
(function() {
    'use strict';

    var st = new ShardingTest({shards: 2});

    var mongos = st.s0;
    var coll = mongos.getCollection("foo.bar");
    var admin = mongos.getDB("admin");

    assert.commandWorked(admin.runCommand({enableSharding: coll.getDB().getName()}));
    printjson(admin.runCommand({movePrimary: coll.getDB().getName(), to: st.shard0.shardName}));
    assert.commandWorked(admin.runCommand({shardCollection: coll.getFullName(), key: {_id: 1}}));

    assert.commandWorked(admin.runCommand({split: coll.getFullName(), middle: {_id: 0}}));
    assert.commandWorked(
        admin.runCommand({moveChunk: coll.getFullName(), find: {_id: 0}, to: st.shard1.shardName}));

    st.printShardingStatus();

    // Insert 100 documents, half of which have an extra field
    for (var i = -50; i < 50; i++) {
        var doc = {};
        if (i >= 0)
            doc.positiveId = true;
        assert.writeOK(coll.insert(doc));
    }

    //
    //
    // Ensure projecting out all fields still returns the same number of documents
    assert.eq(100, coll.find({}).itcount());
    assert.eq(100, coll.find({}).sort({positiveId: 1}).itcount());
    assert.eq(100, coll.find({}, {_id: 0, positiveId: 0}).itcount());
    // Can't remove sort key from projection (SERVER-11877) but some documents will still be empty
    assert.eq(100, coll.find({}, {_id: 0}).sort({positiveId: 1}).itcount());

    //
    //
    // Ensure projecting out all fields still returns the same ordering of documents
    var assertLast50Positive = function(sortedDocs) {
        assert.eq(100, sortedDocs.length);
        var positiveCount = 0;
        for (var i = 0; i < sortedDocs.length; ++i) {
            if (sortedDocs[i].positiveId) {
                positiveCount++;
            } else {
                // Make sure only the last set of documents have "positiveId" set
                assert.eq(positiveCount, 0);
            }
        }
        assert.eq(positiveCount, 50);
    };

    assertLast50Positive(coll.find({}).sort({positiveId: 1}).toArray());
    assertLast50Positive(coll.find({}, {_id: 0}).sort({positiveId: 1}).toArray());

    st.stop();
})();