CRUD operations with Sequelize in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Sequelize create operation?

Consider this Express route using Sequelize to create a new user. What will be the JSON response after a successful creation?

Express

app.post('/users', async (req, res) => {
  try {
    const user = await User.create({ name: 'Alice', age: 30 });
    res.json(user);
  } catch (error) {
    res.status(500).json({ error: 'Failed to create user' });
  }
});

A {"name": "Alice", "age": 30}

B {"error": "Failed to create user"}

C null

D {"id": 1, "name": "Alice", "age": 30, "createdAt": "<date>", "updatedAt": "<date>"}

💡 Hint

Sequelize returns the full created instance including auto-generated fields.

Sequelize's create method returns the full instance including auto-generated fields like id, createdAt, and updatedAt. The response sends this full object as JSON.

❓ state_output

intermediate

What is the result of this Sequelize update operation?

Given this code snippet updating a user's age, what will be the value of updatedUser.age after the operation?

Express

const updatedUser = await User.update({ age: 35 }, { where: { name: 'Alice' }, returning: true, plain: true });
console.log(updatedUser.age);

A 35

B undefined

C 30

D null

💡 Hint

The returning: true option returns the updated instance.

With returning: true and plain: true, Sequelize returns an array where the second element is the updated instance. So updatedUser.age is undefined because updatedUser is an array.

🔧 Debug

advanced

Why does this Sequelize delete operation fail with an error?

This code attempts to delete a user but throws an error. What is the cause?

Express

app.delete('/users/:id', async (req, res) => {
  try {
    await User.destroy({ id: req.params.id });
    res.json({ message: 'User deleted' });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

A The 'where' clause is missing in the destroy method.

B The 'id' parameter is not converted to a number.

C The route method should be 'post' instead of 'delete'.

D The destroy method does not exist in Sequelize.

💡 Hint

Sequelize's destroy method requires a 'where' object to specify which records to delete.

The destroy method requires a where option to specify the condition. Passing { id: req.params.id } directly is incorrect and causes an error.

📝 Syntax

advanced

Which option correctly retrieves all users older than 25 using Sequelize?

Select the correct Sequelize query to find all users with age greater than 25.

A User.findAll({ where: { age: { [Op.gt]: 25 } } })

B User.findAll({ where: { age: { $gt: 25 } } })

C User.findAll({ where: { age: '>25' } })

D User.findAll({ age: { gt: 25 } })

💡 Hint

Sequelize uses the Op object for operators like greater than.

Sequelize requires the use of Op.gt inside the where clause to filter by greater than.

🧠 Conceptual

expert

What happens if you call Sequelize's update method without the 'where' option?

Consider this code: await User.update({ age: 40 }); What will be the result?

A Sequelize throws a runtime error about missing 'where' clause.

B No records will be updated because 'where' is missing.

C All user records in the database will have their age set to 40.

D Only the first user record will be updated.

💡 Hint

Without a 'where' clause, Sequelize updates all rows by default.

If you omit the where option, Sequelize applies the update to all rows in the table.