Why server-side logic reduces client complexity in Supabase - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call a Supabase function from the client.

Supabase

const { data, error } = await supabase.rpc('[1]')

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

AgetUserProfile

BdeleteItem

CupdateRecord

DfetchData

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name that modifies data instead of fetching it.

Leaving the function name blank.

The client calls the server-side function named getUserProfile to get user data.

2fill in blank

medium

Complete the code to handle the server response correctly.

Supabase

if (error) { console.error([1]) } else { console.log(data) }

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

Aerror.message

Bdata

Cresponse

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Logging the data instead of the error message.

Using an undefined variable like response.

When there is an error, error.message contains the error details to log.

3fill in blank

hard

Fix the error in the server-side function call to reduce client complexity.

Supabase

const { data, error } = await supabase.rpc('getUserData', { user_id: [1] })

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

Auserid

Buser_id

CuserId

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using camelCase or other variations that don't match the server parameter.

Leaving the parameter name incorrect causing runtime errors.

The parameter name must match the server function's expected argument user_id.

4fill in blank

hard

Fill both blanks to create a server-side function that returns user info and reduces client logic.

Supabase

create function getUserInfo([1]) returns json as $$ select * from users where id = [2]; $$ language sql;

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

Auser_id integer

BuserId integer

Cuser_id

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Using camelCase in SQL function parameters.

Mismatching parameter name in query.

The function parameter must be declared as user_id integer and used as user_id in the query to match the argument.

5fill in blank

hard

Fill all three blanks to show how server-side logic simplifies client code by handling filtering and sorting.

Supabase

const { data, error } = await supabase.rpc('getFilteredData', { filter: [1], sortBy: [2], order: [3] })

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

A'active'

B'created_at'

C'desc'

D'name'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong field names for sorting.

Not quoting string values.

The client sends filter 'active', sorts by 'created_at', and orders descending 'desc'. The server handles the logic, keeping client simple.

Practice

1. Why does moving logic to the server reduce complexity on the client side in Supabase?

easy

A. Because the client does not need to handle complex rules or validations.

B. Because the client can store all data locally without syncing.

C. Because the client runs faster without any network calls.

D. Because the client can directly modify the database schema.

Solution

1. Step 1: Understand client responsibilities

   The client usually handles user interface and simple logic but complex rules can make it bulky.

2. Step 2: Role of server-side logic

   Moving complex rules to the server means the client only sends requests and receives results, simplifying its code.

3. Final Answer:

   Because the client does not need to handle complex rules or validations. -> Option A

4. Quick Check:

   Server logic reduces client complexity = A [OK]

Hint: Server logic handles rules, client stays simple [OK]

Common Mistakes:

• Thinking client stores all data locally
• Assuming client runs faster without network
• Believing client can change database schema

2. Which of the following is the correct way to define a PostgreSQL function in Supabase for server-side logic?

easy

A. CREATE FUNCTION check_user() RETURNS void AS $$ BEGIN IF NEW.age < 18 THEN RAISE EXCEPTION 'Too young'; END IF; END; $$ LANGUAGE plpgsql;

B. CREATE FUNCTION check_user RETURNS void BEGIN IF NEW.age < 18 THEN RAISE EXCEPTION 'Too young'; END IF; END;

C. FUNCTION check_user() RETURNS void { IF NEW.age < 18 THEN THROW 'Too young'; }

D. CREATE PROCEDURE check_user() BEGIN IF NEW.age < 18 THEN RAISE ERROR 'Too young'; END IF; END;

Solution

1. Step 1: Check PostgreSQL function syntax

   PostgreSQL functions use CREATE FUNCTION, specify RETURNS, and use $$ to wrap the body with LANGUAGE plpgsql.

2. Step 2: Identify correct syntax in options

   CREATE FUNCTION check_user() RETURNS void AS $$ BEGIN IF NEW.age < 18 THEN RAISE EXCEPTION 'Too young'; END IF; END; $$ LANGUAGE plpgsql; correctly uses CREATE FUNCTION, RETURNS void, $$ body $$, and LANGUAGE plpgsql.

3. Final Answer:

   CREATE FUNCTION check_user() RETURNS void AS $$ BEGIN IF NEW.age < 18 THEN RAISE EXCEPTION 'Too young'; END IF; END; $$ LANGUAGE plpgsql; -> Option A

4. Quick Check:

   Correct PostgreSQL function syntax = D [OK]

Hint: Look for CREATE FUNCTION with $$ and LANGUAGE plpgsql [OK]

Common Mistakes:

• Omitting RETURNS keyword
• Missing $$ around function body
• Using THROW or RAISE ERROR instead of RAISE EXCEPTION

3. Given this Supabase trigger function, what happens when a new user with age 16 is inserted?

CREATE FUNCTION check_age() RETURNS trigger AS $$ BEGIN IF NEW.age < 18 THEN RAISE EXCEPTION 'User too young'; END IF; RETURN NEW; END; $$ LANGUAGE plpgsql; CREATE TRIGGER age_check BEFORE INSERT ON users FOR EACH ROW EXECUTE FUNCTION check_age();

medium

A. The insert succeeds and the user is added.

B. The insert succeeds but age is set to 18 automatically.

C. The insert fails with an error 'User too young'.

D. The insert is ignored silently without error.

Solution

1. Step 1: Understand trigger behavior

   The trigger runs BEFORE INSERT and checks if NEW.age is less than 18.

2. Step 2: Analyze condition for age 16

   Since 16 < 18, the trigger raises an exception 'User too young', which stops the insert.

3. Final Answer:

   The insert fails with an error 'User too young'. -> Option C

4. Quick Check:

   Trigger raises error on age < 18 = C [OK]

Hint: Trigger raises error if condition met, blocking insert [OK]

Common Mistakes:

• Thinking insert succeeds despite error
• Assuming age auto-corrects to 18
• Believing insert is ignored without error

4. You wrote this trigger function in Supabase but it does not block invalid inserts as expected:

CREATE FUNCTION check_age() RETURNS trigger AS $$ BEGIN IF NEW.age < 18 THEN RETURN NULL; END IF; RETURN NEW; END; $$ LANGUAGE plpgsql;

What is the main issue?

medium

A. The function must return OLD instead of NEW.

B. Returning NULL in BEFORE INSERT triggers causes the row to be skipped silently.

C. The trigger is missing the EXECUTE FUNCTION statement.

D. The function should use RAISE EXCEPTION to block inserts, not RETURN NULL.

Solution

1. Step 1: Understand RETURN NULL in triggers

   In BEFORE INSERT triggers, returning NULL silently skips the row without error.

2. Step 2: Correct way to block insert

   To block inserts with an error, the function must RAISE EXCEPTION instead of returning NULL.

3. Final Answer:

   The function should use RAISE EXCEPTION to block inserts, not RETURN NULL. -> Option D

4. Quick Check:

   Use RAISE EXCEPTION to block inserts = A [OK]

Hint: RETURN NULL skips silently; use RAISE EXCEPTION to block [OK]

Common Mistakes:

• Returning NULL expecting error
• Forgetting EXECUTE FUNCTION in trigger
• Returning OLD in insert triggers

5. You want to reduce client complexity by enforcing a rule that users must have unique emails and be at least 18 years old. Which combination of Supabase features best achieves this with minimal client code?

hard

A. Check email uniqueness and age on the client before sending data to Supabase.

B. Use a UNIQUE constraint on email and a BEFORE INSERT trigger function that raises an exception if age < 18.

C. Use a BEFORE INSERT trigger to check email uniqueness and age, but no database constraints.

D. Use only a UNIQUE constraint on email and let the client check age.

Solution

1. Step 1: Enforce email uniqueness

   A UNIQUE constraint on the email column ensures no duplicates at the database level.

2. Step 2: Enforce age rule server-side

   A BEFORE INSERT trigger function can check age and raise an exception if under 18, blocking invalid inserts.

3. Final Answer:

   Use a UNIQUE constraint on email and a BEFORE INSERT trigger function that raises an exception if age < 18. -> Option B

4. Quick Check:

   Database constraints + trigger enforce rules, reduce client code = B [OK]

Hint: Combine UNIQUE constraint and trigger for full server-side checks [OK]

Common Mistakes:

• Relying only on client-side checks
• Using triggers without constraints for uniqueness
• Ignoring age validation on server