Calling functions via RPC in Supabase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does RPC stand for in the context of Supabase?

RPC stands for Remote Procedure Call. It allows you to call database functions directly from your application.

beginner

How do you call a PostgreSQL function using Supabase client?

You use the `rpc` method on the Supabase client, passing the function name and parameters as an object.

intermediate

Why use RPC functions instead of direct queries in Supabase?

RPC functions encapsulate logic in the database, improve security, and simplify client code by reusing database functions.

beginner

What is the correct way to handle parameters when calling an RPC function in Supabase?

Parameters should be passed as an object with keys matching the function's argument names.

intermediate

What happens if an RPC function called via Supabase returns an error?

The Supabase client returns an error object that you can check and handle in your application code.

Which Supabase client method is used to call a PostgreSQL function remotely?

A callFunction

B rpc

C query

D execute

The `rpc` method is designed to call PostgreSQL functions remotely in Supabase.

How should parameters be passed when calling an RPC function in Supabase?

A As an object with named keys

B As a JSON string

C As an array of values

D As separate arguments

Parameters must be passed as an object with keys matching the function's argument names.

What is a key benefit of using RPC functions in Supabase?

A They simplify client code by reusing database logic

B They automatically scale the database

C They replace the need for authentication

D They allow direct access to the file system

RPC functions encapsulate logic in the database, making client code simpler and more secure.

If an RPC call returns an error, what should you do in your application?

A Call the function again without changes

B Ignore it and continue

C Restart the database

D Check the error object and handle it appropriately

You should check the error object returned by the Supabase client and handle errors gracefully.

Which of the following is NOT true about calling functions via RPC in Supabase?

A RPC calls use the `rpc` method on the client

B RPC calls can improve security by limiting direct table access

C RPC functions must be written in JavaScript

D RPC functions run inside the PostgreSQL database

RPC functions are PostgreSQL functions, typically written in SQL or PL/pgSQL, not JavaScript.

Explain how to call a PostgreSQL function using Supabase RPC and why this method is useful.

Think about how the client talks to the database and why hiding logic there helps.

Describe how error handling works when calling functions via RPC in Supabase.

Consider what happens if the database function fails and how your app should respond.

Practice

1. What does supabase.rpc() do in a Supabase app?

easy

A. Creates a new table in the database

B. Uploads files to storage

C. Fetches user authentication details

D. Calls a custom database function remotely

Solution

1. Step 1: Understand the purpose of supabase.rpc()

   This method is designed to call remote procedure calls (RPC), which are custom functions defined in the database.

2. Step 2: Identify what supabase.rpc() does in the app context

   It runs these custom functions securely from the app, allowing logic to stay in the database.

3. Final Answer:

   Calls a custom database function remotely -> Option D

4. Quick Check:

   RPC calls = custom database functions [OK]

Hint: RPC means running database functions remotely [OK]

Common Mistakes:

• Confusing RPC with file uploads
• Thinking it creates tables
• Assuming it handles user login

2. Which is the correct way to call a function named get_user_data with parameter { user_id: 5 } using Supabase RPC?

easy

A. supabase.rpc('get_user_data', { user_id: 5 })

B. supabase.call('get_user_data', 5)

C. supabase.function('get_user_data', { id: 5 })

D. supabase.execute('get_user_data', user_id=5)

Solution

1. Step 1: Recall the syntax of supabase.rpc()

   The method takes the function name as a string and an object with parameters.

2. Step 2: Match the correct syntax with the options

   supabase.rpc('get_user_data', { user_id: 5 }) correctly uses supabase.rpc('function_name', { params }) format.

3. Final Answer:

   supabase.rpc('get_user_data', { user_id: 5 }) -> Option A

4. Quick Check:

   Correct RPC call syntax = supabase.rpc('get_user_data', { user_id: 5 }) [OK]

Hint: Use rpc('function', {params}) format [OK]

Common Mistakes:

• Using wrong method names like call or execute
• Passing parameters as separate arguments
• Using incorrect parameter keys

3. Given this code snippet:

const { data, error } = await supabase.rpc('multiply', { a: 3, b: 4 });
console.log(data);

What will be printed if the multiply function returns the product of a and b?

medium

A. 7

B. 12

C. undefined

D. Error

Solution

1. Step 1: Understand the function call and parameters

   The function multiply is called with a=3 and b=4.

2. Step 2: Calculate the expected return value

   Since the function returns the product, 3 * 4 = 12.

3. Final Answer:

   12 -> Option B

4. Quick Check:

   3 times 4 = 12 [OK]

Hint: Multiply parameters to find output [OK]

Common Mistakes:

• Adding instead of multiplying
• Assuming no return value
• Confusing data with error

4. You wrote this code:

const { data, error } = await supabase.rpc('get_user', { user_id: 10 });
console.log(data);

But you get an error saying the function does not exist. What is the likely cause?

medium

A. Parameters must be passed as an array, not an object

B. You forgot to import supabase client

C. The function name is misspelled or missing in the database

D. RPC calls do not support parameters

Solution

1. Step 1: Analyze the error message

   The error says the function does not exist, indicating a problem with the function name or its presence in the database.

2. Step 2: Check common causes for missing function errors

   Usually, the function is either misspelled or not created in the database schema.

3. Final Answer:

   The function name is misspelled or missing in the database -> Option C

4. Quick Check:

   Function missing error = wrong or absent function [OK]

Hint: Check function spelling and existence in DB [OK]

Common Mistakes:

• Passing parameters incorrectly
• Assuming import errors cause this
• Thinking RPC disallows parameters

5. You want to create a Supabase RPC call to get the total sales for a given store_id. The database function is named total_sales and takes store_id as input. Which code snippet correctly calls this function and handles errors?

hard

A. const { data, error } = await supabase.rpc('total_sales', { store_id }); if (error) console.error(error); else console.log(data);

B. const result = supabase.call('total_sales', store_id); console.log(result);

C. const { data } = await supabase.rpc('total_sales', store_id); console.log(data);

D. const { data, error } = supabase.rpc('total_sales', { store: store_id }); if (error) throw error; else console.log(data);

Solution

1. Step 1: Identify correct RPC call syntax with parameters

   The function name is 'total_sales' and parameters must be passed as an object with key matching the function input, here { store_id }.

2. Step 2: Check error handling and async usage

   const { data, error } = await supabase.rpc('total_sales', { store_id }); if (error) console.error(error); else console.log(data); uses await, destructures data and error, and handles error properly with console.error.

3. Final Answer:

   const { data, error } = await supabase.rpc('total_sales', { store_id }); if (error) console.error(error); else console.log(data); -> Option A

4. Quick Check:

   Correct RPC call with error check = const { data, error } = await supabase.rpc('total_sales', { store_id }); if (error) console.error(error); else console.log(data); [OK]

Hint: Use await, pass params as object, check error [OK]

Common Mistakes:

• Passing parameters incorrectly (not as object)
• Ignoring error handling
• Using wrong method names like call