CRUD operations with Sequelize in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new record using Sequelize.

Express

const newUser = await User.[1]({ name: 'Alice', email: '[e-mail]' });

Drag options to blanks, or click blank then click option'

Acreate

BfindAll

Cupdate

Ddestroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using findAll instead of create will only fetch data, not add new data.

Using update or destroy will modify or delete data, not create.

The create method is used to add a new record to the database in Sequelize.

2fill in blank

medium

Complete the code to find all users with Sequelize.

Express

const users = await User.[1]();

Drag options to blanks, or click blank then click option'

Adestroy

Bcreate

CfindAll

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using create will add data, not fetch it.

Using update or destroy will change or delete data, not fetch.

The findAll method retrieves all records from the database table.

3fill in blank

hard

Fix the error in the update operation code.

Express

await User.[1]({ name: 'Bob' }, { where: { id: 5 } });

Drag options to blanks, or click blank then click option'

Adestroy

Bcreate

CfindAll

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using create will add new data instead of updating.

Using findAll fetches data but does not update.

The update method updates existing records matching the where condition.

4fill in blank

hard

Fill both blanks to delete a user by id using Sequelize.

Express

await User.[1]({ where: { id: [2] } });

Drag options to blanks, or click blank then click option'

Adestroy

Bupdate

C5

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using update or create will not delete records.

Passing a wrong id will delete the wrong user or none.

The destroy method deletes records matching the where condition. Here, the user with id 5 is deleted.

5fill in blank

hard

Fill all three blanks to find a user by primary key and update their email.

Express

const user = await User.[1](10);
if (user) {
  await user.[2]({ email: '[e-mail]' });
  await user.[3]();
}

Drag options to blanks, or click blank then click option'

AfindByPk

Bupdate

Csave

Ddestroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using destroy will delete the user instead of updating.

Not calling save after update may not persist changes.

findByPk finds a record by its primary key. Then update changes the email field. Finally, save saves the changes to the database.

Practice

1. Which Sequelize method is used to add a new record to the database?

easy

A. update()

B. findAll()

C. create()

D. destroy()

Solution

1. Step 1: Understand CRUD operations

   CRUD stands for Create, Read, Update, Delete. Each operation has a matching Sequelize method.

2. Step 2: Match method to Create operation

   The create() method is used to add new records to the database.

3. Final Answer:

   create() -> Option C

4. Quick Check:

   Create = create() [OK]

Hint: Create means add new, so use create() method [OK]

Common Mistakes:

• Confusing create() with findAll() which reads data
• Using update() to add new records
• Using destroy() which deletes records

2. Which of the following is the correct syntax to update a user's name to 'Alice' where id is 5 using Sequelize?

easy

A. User.update({ name: 'Alice' }, { where: { id: 5 } })

B. User.update({ where: { id: 5 } }, { name: 'Alice' })

C. User.update('Alice', { id: 5 })

D. User.update({ id: 5 }, { name: 'Alice' })

Solution

1. Step 1: Recall Sequelize update syntax

   The update method takes two arguments: the new values object, and the options object with a where clause.

2. Step 2: Match correct argument order and structure

   User.update({ name: 'Alice' }, { where: { id: 5 } }) correctly places the new values first and the where condition second.

3. Final Answer:

   User.update({ name: 'Alice' }, { where: { id: 5 } }) -> Option A

4. Quick Check:

   update(values, { where }) = User.update({ name: 'Alice' }, { where: { id: 5 } }) [OK]

Hint: Update needs values first, then where condition [OK]

Common Mistakes:

• Swapping the order of arguments
• Passing values inside where instead of separate object
• Using strings instead of objects for values

3. Given the code:

const users = await User.findAll({ where: { age: { [Op.gt]: 18 } } });
console.log(users.length);

What will console.log(users.length) output?

medium

A. The total number of users in the database

B. An error because Op.gt is not defined

C. Always 0 because findAll returns undefined

D. The number of users older than 18

Solution

1. Step 1: Understand findAll with where clause

   The findAll method returns all records matching the where condition. Here, it filters users with age greater than 18.

2. Step 2: Determine what users.length represents

   users is an array of matching records, so users.length is the count of users older than 18.

3. Final Answer:

   The number of users older than 18 -> Option D

4. Quick Check:

   findAll with condition returns matching array length [OK]

Hint: findAll returns array; length counts matching records [OK]

Common Mistakes:

• Thinking findAll returns undefined or null
• Ignoring the where condition filtering
• Assuming Op.gt is undefined without importing

4. What is wrong with this code snippet for deleting a user by id?

await User.destroy(id);

medium

A. destroy requires an object with a where clause, not just id

B. destroy cannot be awaited

C. destroy only works with arrays, not single values

D. destroy needs a callback function

Solution

1. Step 1: Recall destroy method signature

   Sequelize's destroy method expects an options object with a where property to specify which records to delete.

2. Step 2: Identify incorrect argument usage

   Passing just the id directly is incorrect; it must be inside { where: { id: id } }.

3. Final Answer:

   destroy requires an object with a where clause, not just id -> Option A

4. Quick Check:

   destroy({ where: { id } }) is correct [OK]

Hint: destroy needs where inside an object, not just id [OK]

Common Mistakes:

• Passing id directly instead of inside where
• Not awaiting asynchronous destroy call
• Expecting destroy to accept callback

5. You want to update multiple users' status to 'active' where their last login was before 2023-01-01. Which Sequelize code correctly does this?

hard

A. User.update({ where: { lastLogin: { [Op.lt]: '2023-01-01' } } }, { status: 'active' })

B. User.update({ status: 'active' }, { where: { lastLogin: { [Op.lt]: new Date('2023-01-01') } } })

C. User.update('active', { lastLogin: { [Op.lt]: new Date('2023-01-01') } })

D. User.update({ status: 'active' }, { lastLogin: { [Op.lt]: new Date('2023-01-01') } })

Solution

1. Step 1: Understand update method parameters

   The first argument is the values to update, the second is an options object with a where clause to filter records.

2. Step 2: Check correct use of Op.lt and date object

   User.update({ status: 'active' }, { where: { lastLogin: { [Op.lt]: new Date('2023-01-01') } } }) correctly uses [Op.lt] with a Date object inside the where clause.

3. Step 3: Verify argument order and structure

   The other options have incorrect argument order or missing where wrapper.

4. Final Answer:

   User.update({ status: 'active' }, { where: { lastLogin: { [Op.lt]: new Date('2023-01-01') } } }) -> Option B

5. Quick Check:

   update(values, { where: condition }) with Op.lt date [OK]

Hint: Update needs values first, then where with Op.lt date [OK]

Common Mistakes:

• Swapping values and where arguments
• Using string instead of Date object for date comparison
• Omitting where wrapper around condition