Sequelize ORM setup in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Sequelize model definition produce?

Consider this Sequelize model definition for a User. What will be the data type of the 'age' column in the database?

Express

const User = sequelize.define('User', {
  name: {
    type: Sequelize.STRING,
    allowNull: false
  },
  age: {
    type: Sequelize.INTEGER,
    allowNull: true
  }
});

A A column named 'age' with string type that cannot be null

B A column named 'age' with integer type that can be null

C A column named 'age' with boolean type that can be null

D A column named 'age' with date type that cannot be null

💡 Hint

Look at the 'type' and 'allowNull' properties in the model definition.

The 'age' field is defined with Sequelize.INTEGER and allowNull: true, so it creates an integer column that can be null.

📝 Syntax

intermediate

Which option correctly initializes Sequelize with SQLite?

You want to create a Sequelize instance using SQLite as the database. Which code snippet correctly does this?

A const sequelize = new Sequelize('sqlite', 'memory');

B const sequelize = new Sequelize('sqlite::memory:');

C const sequelize = new Sequelize({ dialect: 'sqlite', storage: ':memory:' });

D const sequelize = new Sequelize('sqlite://memory');

💡 Hint

Check the Sequelize docs for SQLite connection strings.

The correct ways to initialize Sequelize with an in-memory SQLite database are using the connection string 'sqlite::memory:' or the object with dialect and storage.

🔧 Debug

advanced

Why does this Sequelize sync code throw an error?

Given this code snippet, why does calling sequelize.sync() throw a TypeError?

Express

import { Sequelize } from 'sequelize';

const sequelize = Sequelize('sqlite::memory:');

await sequelize.sync();

A Because 'await' cannot be used outside async functions

B Because 'sync' is not a method on Sequelize instances

C Because SQLite is not supported by Sequelize

D Because Sequelize must be called with 'new' keyword to create an instance

💡 Hint

Check how Sequelize instances are created.

Sequelize is a class and must be instantiated with 'new'. Calling Sequelize() without 'new' returns undefined, causing sync() to fail.

❓ state_output

advanced

What is the output after creating and saving a User instance?

Given this code, what will be logged to the console?

Express

const { Sequelize, DataTypes } = require('sequelize');
const sequelize = new Sequelize('sqlite::memory:');

const User = sequelize.define('User', {
  username: DataTypes.STRING
});

(async () => {
  await sequelize.sync();
  const user = User.build({ username: 'alice' });
  await user.save();
  console.log(user.id);
})();

A 1

B undefined

C null

D Throws an error because 'id' is not defined

💡 Hint

Sequelize auto-generates primary keys named 'id' by default.

After saving, Sequelize assigns an auto-incremented 'id' starting at 1 to the instance.

🧠 Conceptual

expert

Which option best describes Sequelize's 'sync' method behavior?

What does calling sequelize.sync({ force: true }) do in a Sequelize setup?

A Only creates tables if they do not exist, without dropping anything

B Updates existing tables without dropping them

C Drops all tables and recreates them according to model definitions

D Deletes all data from tables but keeps the structure intact

💡 Hint

Check the meaning of 'force' in Sequelize sync options.

Using 'force: true' drops all tables and recreates them fresh, which deletes all data.