fix(populate): set populated docs in correct order when populating virtual underneath doc array with justOne

lib/helpers/populate/assignRawDocsToIdStructure.js

@@ -32,9 +32,13 @@ const kHasArray = Symbol('mongoose#assignRawDocsToIdStructure#hasArray');
  */
 
 function assignRawDocsToIdStructure(rawIds, resultDocs, resultOrder, options, recursed) {
-  // honor user specified sort order
+  // honor user specified sort order, unless we're populating a single
+  // virtual underneath an array (e.g. populating `employees.mostRecentShift` where
+  // `mostRecentShift` is a virtual with `justOne`)
   const newOrder = [];
-  const sorting = options.sort && rawIds.length > 1;
+  const sorting = options.isVirtual && options.justOne && rawIds.length > 1
+    ? false :
+    options.sort && rawIds.length > 1;
   const nullIfNotFound = options.$nullIfNotFound;
   let doc;
   let sid;

lib/helpers/populate/assignVals.js

@@ -19,7 +19,8 @@ module.exports = function assignVals(o) {
   // `o.options` contains options explicitly listed in `populateOptions`, like
   // `match` and `limit`.
   const populateOptions = Object.assign({}, o.options, userOptions, {
-    justOne: o.justOne
+    justOne: o.justOne,
+    isVirtual: o.isVirtual
   });
   populateOptions.$nullIfNotFound = o.isVirtual;
   const populatedModel = o.populatedModel;

test/model.populate.test.js

@@ -10694,4 +10694,86 @@ describe('model: populate:', function() {
       [company._id.toString(), company2._id.toString()]
     );
   });
+
+  it('sets populated docs in correct order when populating virtual underneath document array with justOne (gh-14018)', async function() {
+    const shiftSchema = new mongoose.Schema({
+      employeeId: mongoose.Types.ObjectId,
+      startedAt: Date,
+      endedAt: Date
+    });
+    const Shift = db.model('Shift', shiftSchema);
+
+    const employeeSchema = new mongoose.Schema({
+      name: String
+    });
+    employeeSchema.virtual('mostRecentShift', {
+      ref: Shift,
+      localField: '_id',
+      foreignField: 'employeeId',
+      options: {
+        sort: { startedAt: -1 }
+      },
+      justOne: true
+    });
+    const storeSchema = new mongoose.Schema({
+      location: String,
+      employees: [employeeSchema]
+    });
+    const Store = db.model('Store', storeSchema);
+
+    const store = await Store.create({
+      location: 'Tashbaan',
+      employees: [
+        { _id: '0'.repeat(24), name: 'Aravis' },
+        { _id: '1'.repeat(24), name: 'Shasta' }
+      ]
+    });
+
+    const employeeAravis = store.employees
+      .find(({ name }) => name === 'Aravis');
+    const employeeShasta = store.employees
+      .find(({ name }) => name === 'Shasta');
+
+    await Shift.insertMany([
+      { employeeId: employeeAravis._id, startedAt: new Date('2011-06-01'), endedAt: new Date('2011-06-02') },
+      { employeeId: employeeAravis._id, startedAt: new Date('2013-06-01'), endedAt: new Date('2013-06-02') },
+      { employeeId: employeeShasta._id, startedAt: new Date('2015-06-01'), endedAt: new Date('2015-06-02') }
+    ]);
+
+    const storeWithMostRecentShifts = await Store.findOne({ location: 'Tashbaan' })
+      .populate('employees.mostRecentShift')
+      .select('-__v')
+      .exec();
+    assert.equal(
+      storeWithMostRecentShifts.employees[0].mostRecentShift.employeeId.toHexString(),
+      '0'.repeat(24)
+    );
+    assert.equal(
+      storeWithMostRecentShifts.employees[1].mostRecentShift.employeeId.toHexString(),
+      '1'.repeat(24)
+    );
+
+    await Shift.findOne({ employeeId: employeeAravis._id }).sort({ startedAt: 1 }).then((s) => s.deleteOne());
+
+    const storeWithMostRecentShiftsNew = await Store.findOne({ location: 'Tashbaan' })
+      .populate('employees.mostRecentShift')
+      .select('-__v')
+      .exec();
+    assert.equal(
+      storeWithMostRecentShiftsNew.employees[0].mostRecentShift.employeeId.toHexString(),
+      '0'.repeat(24)
+    );
+    assert.equal(
+      storeWithMostRecentShiftsNew.employees[0].mostRecentShift.startedAt.toString(),
+      new Date('2013-06-01').toString()
+    );
+    assert.equal(
+      storeWithMostRecentShiftsNew.employees[1].mostRecentShift.employeeId.toHexString(),
+      '1'.repeat(24)
+    );
+    assert.equal(
+      storeWithMostRecentShiftsNew.employees[1].mostRecentShift.startedAt.toString(),
+      new Date('2015-06-01').toString()
+    );
+  });
 });