How to populate mongoose result with subdocument's array?

Question

I'm trying to populate a mongoose result with a subdocument, but I can't.

I tried this code, but it get this error:

MissingSchemaError: Schema hasn't been registered for model "department.subDepartment"

Mongoose schema:

const subDepartmentSchema = new Schema({
  name: { type: String, required: true },
  city: { type: String, required: true }
})

const DepartmentSchema = new Schema({
  name: { type: String, required: true },
  city: { type: String, required: true },
  subDepartment: [subDepartmentSchema]
}
)

const UserSchema = new Schema({
  name: { type: String, required: true },
  city: { type: String, required: true },
  department: { type: Schema.Types.ObjectId, required: true, ref: 'department' },
  subDepartment: { type: Schema.Types.ObjectId, required: true, ref: 'department.subDepartment' },
  active: { type: Boolean, required: true, default: true }
}
)

const Department = mongoose.model('department', DepartmentSchema)
const User = mongoose.model('user', UserSchema)

Function:

const result = await User.findById('5d31dfeec4d0af0cb2f448fc').populate('subDepartment')
console.log(JSON.stringify(result.subDepartment))

On the DB I must have only two documents (department and user), subDepartment should be a Department's subdocument

How can I populate 'subDepartment'?

Answer 1

You can't do populate with nested fields like departments.subDepartments. Instead, you shoud populate the department, and then pick out subdepartments of the departments for the user.

index.js

const app = require("express")();
const morgan = require("morgan");
const bodyParser = require("body-parser");
const mongoose = require("mongoose");
const models = require("./models");

app.use(morgan("dev"));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.post("/init", async (req, res) => {
  const department = await models.Department.create({
    name: "ICT",
    city: "CA",
    subDepartments: {
      name: "Yolo",
      city: "Solo",
    },
  });
  const user = await models.User.create({
    name: "John Wick",
    city: "NY",
    department: department._id,
  });
  return res.status(201).send({
    message: "Created",
    data: {
      user,
      department,
    },
  });
});
app.get("/users", async (req, res) => {
  const user = await models.User.findOne().populate("department");
  return res.send({ user });
});

mongoose.connect("mongodb://root:toor@0.0.0.0:27017/stackoverflow");
mongoose.connection.on("error", err => console.error(err));
app.listen(3000, () => console.log("Listening on :3000"));

models.js

const mongoose = require("mongoose");

const Schema = mongoose.Schema;

const DepartmentSchema = new Schema({
  name: { type: String, required: true },
  city: { type: String, required: true },
  subDepartments: [
    {
      name: { type: String, required: true },
      city: { type: String, required: true },
    },
  ],
});

const UserSchema = new Schema({
  name: { type: String, required: true },
  city: { type: String, required: true },
  department: {
    type: Schema.Types.ObjectId,
    required: true,
    ref: "department",
  },
  active: { type: Boolean, required: true, default: true },
});

exports.Department = mongoose.model("department", DepartmentSchema);
exports.User = mongoose.model("user", UserSchema);

GET request to /users will return

{
    "user": {
        "active": true,
        "_id": "5d8aa2c36ac2502b3c33794b",
        "name": "John Wick",
        "city": "NY",
        "department": {
            "_id": "5d8aa2c36ac2502b3c337949",
            "name": "ICT",
            "city": "CA",
            "subDepartments": [
                {
                    "_id": "5d8aa2c36ac2502b3c33794a",
                    "name": "Yolo",
                    "city": "Solo"
                }
            ],
            "__v": 0
        },
        "__v": 0
    }
}

Answer 2

You have not created subDepartment model, just schema, thus you are also referencing the wrong type in DepartmentSchema.

const subDepartment = mongoose.model('subDepartment', subDepartmentSchema) // this line is missing
const DepartmentSchema = new Schema({
  name: { type: String, required: true },
  city: { type: String, required: true },
  subDepartment: [{ type: Schema.Types.ObjectId, ref:'subDepartment'}]
}