index.js

var mongoose = require('mongoose');
mongoose.connect('localhost', 'testing_535');
console.error('mongoose version', mongoose.version);

var OID = mongoose.Types.ObjectId;

var ASchema = new mongoose.Schema({
    square: mongoose.Schema.ObjectId
  , task: Number
});

var A = mongoose.model('A', ASchema);

mongoose.connection.on('open', function () {
  var id = new OID;
  A.create(
      { square: id, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }
    , { square: new OID, task: 1 }, function (err) {
    if (err) return console.error(err.stack||err);
    A.find({}, { square: 1 }, function (err, docs) {
      if (err) return console.error(err.stack||err);
      console.error(docs);
      console.error('next');
      var ids = id.toString();
      A.find({ square: ids }, function (err, docs) {
        if (err) return console.error(err.stack||err);
        console.error('found by id');
        console.error(docs);
        mongoose.connection.db.dropDatabase(function () {
          mongoose.connection.close();
        });
      });
    });
  })
});
/*
...
// Where is "square"?
[ { _id: 4e7fcfb76289dd601f00000f },
  { _id: 4e7fcfb76289dd601f000010 },
  { _id: 4e7fcfb76289dd601f000011 },
  { _id: 4e7fcfb76289dd601f000012 },
  { _id: 4e7fcfb76289dd601f000013 },
  { _id: 4e7fcfb76289dd601f000014 },
  { _id: 4e7fcfb76289dd601f000015 },
  { _id: 4e7fcfb76289dd601f000016 },
  { _id: 4e7fcfb76289dd601f000017 },
  { _id: 4e7fcfb76289dd601f000018 },
  { _id: 4e7fcfb76289dd601f000019 },
  { _id: 4e7fcfb76289dd601f00001a },
  { _id: 4e7fcfb76289dd601f00001b },
  { _id: 4e7fcfb76289dd601f00001c } ]
next
found by id
// All records returned instead of just the first!!
[ { square: 4e7fcfb76289dd601f000001, task: 1, _id: 4e7fcfb76289dd601f00000f },
  { square: 4e7fcfb76289dd601f000002, task: 1, _id: 4e7fcfb76289dd601f000010 },
  { square: 4e7fcfb76289dd601f000003, task: 1, _id: 4e7fcfb76289dd601f000011 },
  { square: 4e7fcfb76289dd601f000004, task: 1, _id: 4e7fcfb76289dd601f000012 },
  { square: 4e7fcfb76289dd601f000005, task: 1, _id: 4e7fcfb76289dd601f000013 },
  { square: 4e7fcfb76289dd601f000006, task: 1, _id: 4e7fcfb76289dd601f000014 },
  { square: 4e7fcfb76289dd601f000007, task: 1, _id: 4e7fcfb76289dd601f000015 },
  { square: 4e7fcfb76289dd601f000008, task: 1, _id: 4e7fcfb76289dd601f000016 },
  { square: 4e7fcfb76289dd601f000009, task: 1, _id: 4e7fcfb76289dd601f000017 },
  { square: 4e7fcfb76289dd601f00000a, task: 1, _id: 4e7fcfb76289dd601f000018 },
  { square: 4e7fcfb76289dd601f00000b, task: 1, _id: 4e7fcfb76289dd601f000019 },
  { square: 4e7fcfb76289dd601f00000c, task: 1, _id: 4e7fcfb76289dd601f00001a },
  { square: 4e7fcfb76289dd601f00000d, task: 1, _id: 4e7fcfb76289dd601f00001b },
  { square: 4e7fcfb76289dd601f00000e, task: 1, _id: 4e7fcfb76289dd601f00001c } ]
*/