CRUD operations with Sequelize in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does CRUD stand for in web development?

CRUD stands for Create, Read, Update, and Delete. These are the four basic operations to manage data in an application.

beginner

How do you create a new record using Sequelize?

Use the Model.create() method with an object containing the data you want to save. For example: User.create({ name: 'Alice', age: 25 }).

beginner

Which Sequelize method is used to find all records matching a condition?

The Model.findAll() method is used to get multiple records. You can pass a where option to filter results, like User.findAll({ where: { age: 25 } }).

intermediate

How do you update a record in Sequelize?

Use Model.update() with the new data and a where condition. For example: User.update({ age: 26 }, { where: { id: 1 } }) updates the user with id 1.

intermediate

What method deletes records in Sequelize and how do you specify which ones?

Use Model.destroy() with a where clause to specify which records to delete. For example: User.destroy({ where: { id: 1 } }) deletes the user with id 1.

Which Sequelize method would you use to add a new user to the database?

A Model.findAll()

B Model.create()

C Model.update()

D Model.destroy()

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

How do you retrieve all records from a table using Sequelize?

A Model.findAll()

B Model.findOne()

C Model.update()

D Model.destroy()

Model.findAll() fetches all records from the table.

What parameter do you use to specify which records to update in Sequelize?

A include

B attributes

C where

D order

The 'where' option specifies the condition to find records to update.

Which method removes records from the database?

A Model.create()

B Model.findAll()

C Model.update()

D Model.destroy()

Model.destroy() deletes records matching the condition.

If you want to update a user's email where id equals 5, which Sequelize method and option do you use?

A Model.update({ email: '[e-mail]' }, { where: { id: 5 } })

B Model.destroy({ where: { id: 5 } })

C Model.findAll({ where: { id: 5 } })

D Model.create({ email: '[e-mail]' })

Model.update() with a 'where' clause updates the record with id 5.

Explain how to perform each CRUD operation using Sequelize methods.

Think about how you add, get, change, and remove data.

Describe how you would update a user's information safely using Sequelize in an Express app.

Focus on the update method and filtering the right record.

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