CRUD operations with supabase-js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What is the output of this Supabase insert operation?

Given the following code snippet using supabase-js, what will be the value of data after execution?

Supabase

const { data, error } = await supabase
  .from('profiles')
  .insert([{ id: '123', username: 'alice' }]);

A An array with the inserted row object: [{ id: '123', username: 'alice' }]

B null

C An empty array []

D A string message confirming insertion

💡 Hint

Think about what supabase-js returns after a successful insert.

When you insert data using supabase-js, the data contains an array of the inserted rows. Here, it will be an array with the inserted object.

❓ Configuration

intermediate

Which option correctly updates a user's email in supabase-js?

You want to update the email of the user with id 'abc123' in the 'users' table. Which code snippet correctly performs this update?

A await supabase.from('users').modify({ email: '[e-mail]' }).filter('id', 'abc123');

B await supabase.from('users').set({ email: '[e-mail]' }).where('id', 'abc123');

C await supabase.from('users').update({ email: '[e-mail]' }).eq('id', 'abc123');

D await supabase.update('users').set({ email: '[e-mail]' }).eq('id', 'abc123');

💡 Hint

Check the supabase-js method names for updating and filtering.

The correct method to update rows is update() and to filter rows is eq(). Option C uses both correctly.

❓ Architecture

advanced

Which architecture best supports real-time updates with supabase-js?

You want your app to show live changes from the 'messages' table without refreshing. Which architecture choice best supports this with supabase-js?

A Use a separate REST API server to push updates to the client.

B Periodically poll the 'messages' table every 5 seconds using supabase-js select queries.

C Fetch all messages once on app load and store locally without updates.

D Use supabase-js subscriptions to listen to changes on 'messages' and update UI accordingly.

💡 Hint

Supabase supports real-time subscriptions natively.

Supabase-js provides real-time subscriptions to listen to database changes. This allows the app to update UI live without polling.

❓ security

advanced

Which option correctly restricts data access in supabase-js using Row Level Security (RLS)?

You want to ensure users can only read their own profiles from the 'profiles' table. Which setup correctly enforces this using supabase-js and RLS?

A Use supabase-js to filter profiles by user id but keep RLS disabled.

B Enable RLS on 'profiles' and create a policy: 'USING (auth.uid() = id)'. Then query normally with supabase-js.

C Enable RLS but do not create any policies; supabase-js will automatically restrict access.

D Disable RLS and filter profiles by user id in supabase-js client code.

💡 Hint

RLS requires explicit policies to restrict access.

Row Level Security must be enabled and a policy created to restrict access. The policy 'USING (auth.uid() = id)' ensures users only access their own rows.

✅ Best Practice

expert

What is the best practice to handle errors in supabase-js CRUD operations?

You perform an insert operation with supabase-js. Which approach correctly handles possible errors?

Supabase

const { data, error } = await supabase.from('tasks').insert([{ title: 'New Task' }]);

A Check if <code>error</code> is not null and handle it before using <code>data</code>.

B Ignore <code>error</code> and assume <code>data</code> is always valid.

C Use try-catch block around the insert call without checking <code>error</code>.

D Only check if <code>data</code> is null to detect errors.

💡 Hint

Supabase-js returns errors separately from data.

Supabase-js returns error separately. Always check if error is present before using data to avoid unexpected issues.