CRUD operations with supabase-js

Introduction

CRUD means Create, Read, Update, and Delete data. Using supabase-js helps you do these actions easily with your database in a web app.

You want to add new user info to your app database.

You need to show a list of items from your database on a webpage.

You want to change details of a product in your database.

You need to remove old or wrong data from your database.

Syntax

Supabase

import { createClient } from '@supabase/supabase-js'

const supabase = createClient('your-supabase-url', 'your-anon-key')

// Create
const { data, error } = await supabase.from('table').insert([{ column: 'value' }])

// Read
const { data, error } = await supabase.from('table').select('*').eq('column', 'value')

// Update
const { data, error } = await supabase.from('table').update({ column: 'newValue' }).eq('id', 1)

// Delete
const { data, error } = await supabase.from('table').delete().eq('id', 1)

Use await because these operations are asynchronous (they take time to finish).

Always check error to handle problems.

Examples

This adds a new user named Anna who is 25 years old.

Supabase

const { data, error } = await supabase.from('users').insert([{ name: 'Anna', age: 25 }])

This gets all users who are 25 years old.

Supabase

const { data, error } = await supabase.from('users').select('*').eq('age', 25)

This changes Anna's age to 26.

Supabase

const { data, error } = await supabase.from('users').update({ age: 26 }).eq('name', 'Anna')

This deletes the user named Anna.

Supabase

const { data, error } = await supabase.from('users').delete().eq('name', 'Anna')

Sample Program

This program connects to Supabase, adds a task, reads tasks not done, updates a task to done, then deletes done tasks. It logs each step's result.

Supabase

import { createClient } from '@supabase/supabase-js'

const supabaseUrl = 'https://xyzcompany.supabase.co'
const supabaseKey = 'public-anonymous-key'
const supabase = createClient(supabaseUrl, supabaseKey)

async function runCRUD() {
  // Create
  let { data: insertData, error: insertError } = await supabase.from('tasks').insert([{ title: 'Learn Supabase', done: false }])
  if (insertError) return console.error('Insert error:', insertError)
  console.log('Inserted:', insertData)

  // Read
  let { data: readData, error: readError } = await supabase.from('tasks').select('*').eq('done', false)
  if (readError) return console.error('Read error:', readError)
  console.log('Tasks not done:', readData)

  // Update
  let { data: updateData, error: updateError } = await supabase.from('tasks').update({ done: true }).eq('title', 'Learn Supabase')
  if (updateError) return console.error('Update error:', updateError)
  console.log('Updated:', updateData)

  // Delete
  let { data: deleteData, error: deleteError } = await supabase.from('tasks').delete().eq('done', true).select('*')
  if (deleteError) return console.error('Delete error:', deleteError)
  console.log('Deleted:', deleteData)
}

runCRUD()

Important Notes

Replace supabaseUrl and supabaseKey with your real project values.

Supabase tables must exist before running these commands.

Use eq to filter rows by column values.

Summary

CRUD lets you manage data: add, get, change, and remove.

supabase-js makes these actions easy with simple commands.

Always handle errors to keep your app stable.

Practice

1. What does the insert() method do in supabase-js when working with a table?

easy

A. Deletes data rows from the table

B. Adds new data rows to the table

C. Updates existing data rows in the table

D. Fetches data rows from the table

Solution

1. Step 1: Understand the purpose of insert()

   The insert() method is used to add new records to a database table.

2. Step 2: Compare with other CRUD methods

   delete() removes data, update() changes data, and select() fetches data. So insert() must add data.

3. Final Answer:

   Adds new data rows to the table -> Option B

4. Quick Check:

   insert() = add data [OK]

Hint: Insert means add new data rows [OK]

Common Mistakes:

• Confusing insert() with update()
• Thinking insert() deletes data
• Mixing insert() with select()

2. Which of the following is the correct syntax to select all rows from a table named users using supabase-js?

easy

A. supabase.from('users').select('*')

B. supabase.select('*').from('users')

C. supabase.from('users').get('*')

D. supabase.query('users').select('*')

Solution

1. Step 1: Recall supabase-js query structure

   The correct method chain starts with from('table') then select() to specify columns.

2. Step 2: Check each option

   supabase.from('users').select('*') matches the correct order and methods. The other options use incorrect method order or invalid methods.

3. Final Answer:

   supabase.from('users').select('*') -> Option A

4. Quick Check:

   from() then select() = correct syntax [OK]

Hint: Use from('table').select('*') to fetch all rows [OK]

Common Mistakes:

• Swapping order of from() and select()
• Using get() instead of select()
• Using query() which is not a supabase-js method

3. What will be the output of this code snippet?

const { data, error } = await supabase.from('products').select('id, name').eq('category', 'books');
console.log(data);

medium

A. An empty array because 'select' needs all fields specified

B. An error because 'eq' is not a valid method

C. All products with all fields regardless of category

D. An array of products with category 'books' showing only id and name fields

Solution

1. Step 1: Understand the query filters and selects

   The select('id, name') picks only those two fields. The eq('category', 'books') filters rows where category equals 'books'.

2. Step 2: Predict the output

   The result data will be an array of objects with only id and name for products in the 'books' category.

3. Final Answer:

   An array of products with category 'books' showing only id and name fields -> Option D

4. Quick Check:

   select + eq filters data correctly [OK]

Hint: eq() filters rows; select() chooses fields [OK]

Common Mistakes:

• Thinking eq() is invalid
• Assuming select() returns all fields
• Expecting error due to method chaining

4. Identify the error in this supabase-js update code:

const { data, error } = await supabase.from('users').update({ age: 30 }).where('id', 5);

medium

A. Missing select() after update()

B. The update method cannot update numeric fields

C. The method where does not exist; should use eq instead

D. The table name 'users' is invalid

Solution

1. Step 1: Check method chaining for update filters

   supabase-js uses eq() to filter rows, not where().

2. Step 2: Confirm other parts

   Updating numeric fields is allowed, select() is optional, and 'users' is a valid table name.

3. Final Answer:

   The method where does not exist; should use eq instead -> Option C

4. Quick Check:

   Use eq() not where() for filtering [OK]

Hint: Use eq() to filter, not where() [OK]

Common Mistakes:

• Using where() instead of eq()
• Thinking update() needs select() always
• Assuming numeric fields can't be updated

5. You want to delete all rows from the orders table where the status is 'cancelled'. Which code snippet correctly performs this action and handles errors?

hard

A. const { error } = await supabase.from('orders').delete().eq('status', 'cancelled'); if (error) console.error(error);

B. const { data } = await supabase.from('orders').remove().eq('status', 'cancelled'); if (data) console.log(data);

C. const { error } = await supabase.from('orders').delete('status', 'cancelled'); if (error) console.error(error);

D. const { error } = await supabase.from('orders').delete().where('status', 'cancelled'); if (error) console.error(error);

Solution

1. Step 1: Identify correct delete syntax with filter

   supabase-js uses delete() followed by eq('column', value) to filter rows to delete.

2. Step 2: Check error handling

   The code checks if error exists and logs it, which is best practice.

3. Final Answer:

   const { error } = await supabase.from('orders').delete().eq('status', 'cancelled'); if (error) console.error(error); -> Option A

4. Quick Check:

   delete() + eq() + error check = correct [OK]

Hint: Use delete().eq() and check error for safe deletion [OK]

Common Mistakes:

• Using remove() instead of delete()
• Using where() instead of eq()
• Not handling errors after delete