Defining models in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Express model definition code?

Consider this Express model definition using Mongoose. What will be the output when trying to create a new user without the required 'email' field?

Express

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema({
  name: String,
  email: { type: String, required: true },
  age: Number
});

const User = mongoose.model('User', userSchema);

async function createUser() {
  try {
    const user = new User({ name: 'Alice', age: 30 });
    await user.save();
    console.log('User saved');
  } catch (error) {
    console.log(error.message);
  }
}

createUser();

A User saved

B TypeError: Cannot read property 'save' of undefined

C Validation failed: email: Path `email` is required.

D SyntaxError: Unexpected token

💡 Hint

Think about what happens when a required field is missing in a Mongoose model.

Since 'email' is marked as required in the schema, trying to save a user without it triggers a validation error. The error message indicates the missing required field.

📝 Syntax

intermediate

Which option correctly defines a Mongoose model with a nested schema?

You want to define a Mongoose model for a blog post that includes a nested 'author' object with 'name' and 'email'. Which code correctly defines this model?

A

const postSchema = new mongoose.Schema({
  title: String,
  author: {
    name: String,
    email: String
  }
});
const Post = mongoose.model('Post', postSchema);

B

const postSchema = new mongoose.Schema({
  title: String,
  author: String
});
const Post = mongoose.model('Post', postSchema);

C

const postSchema = new mongoose.Schema({
  title: String,
  author: [
    { name: String, email: String }
  ]
});
const Post = mongoose.model('Post', postSchema);

D

const authorSchema = new mongoose.Schema({
  name: String,
  email: String
});
const postSchema = new mongoose.Schema({
  title: String,
  author: authorSchema
});
const Post = mongoose.model('Post', postSchema);

💡 Hint

Nested schemas should be defined separately and referenced inside the main schema.

Option D correctly defines a separate schema for 'author' and uses it inside the 'postSchema'. This is the proper way to nest schemas in Mongoose.

🔧 Debug

advanced

Why does this Mongoose model throw a 'Missing schema' error?

Examine the code below. Why does it throw an error 'Missing schema for model "User"' when trying to create a new User?

Express

const mongoose = require('mongoose');

const User = mongoose.model('User');

async function createUser() {
  const user = new User({ name: 'Bob', email: '[e-mail]' });
  await user.save();
  console.log('User saved');
}

createUser();

A Because the model name 'User' is reserved and cannot be used

B Because the schema was not defined before calling mongoose.model('User')

C Because the 'new' keyword is missing when creating the User instance

D Because mongoose.connect() was not called before defining the model

💡 Hint

Check if the schema is passed when defining the model.

Calling mongoose.model('User') without a schema first causes Mongoose to throw 'Missing schema' error. The schema must be defined and passed when creating the model.

❓ state_output

advanced

What is the value of 'user.isActive' after saving this Mongoose model?

Given this schema with a default value, what will be the value of 'isActive' for a new user saved without specifying it?

Express

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema({
  name: String,
  isActive: { type: Boolean, default: true }
});

const User = mongoose.model('User', userSchema);

async function createUser() {
  const user = new User({ name: 'Carol' });
  await user.save();
  console.log(user.isActive);
}

createUser();

A true

B false

C undefined

D null

💡 Hint

Look at the default value set in the schema for 'isActive'.

The schema sets 'isActive' default to true, so when not provided, Mongoose assigns true automatically.

🧠 Conceptual

expert

Which statement about Mongoose schema options is correct?

Consider these statements about Mongoose schema options. Which one is true?

A Setting 'timestamps: true' in schema options automatically adds 'createdAt' and 'updatedAt' fields and updates them on save.

B The 'strict' option set to false means Mongoose will throw an error if extra fields are added to documents.

C Using 'versionKey: false' disables all validation rules on the schema.

D The 'toJSON' option cannot be customized in a Mongoose schema.

💡 Hint

Think about what 'timestamps' option does in Mongoose.

Setting 'timestamps: true' adds 'createdAt' and 'updatedAt' fields automatically and updates them when documents are saved.