Calling functions via RPC in Supabase - Step-by-Step Execution

Process Flow - Calling functions via RPC

Client sends RPC request

↓

Supabase receives request

↓

Supabase calls Postgres function

↓

Function executes in DB

↓

Function returns result

↓

Supabase sends response to client

The client sends a request to Supabase to run a database function. Supabase calls the function in the database and returns the result back to the client.

Execution Sample

Supabase

const { data, error } = await supabase.rpc('get_user_profile', { user_id: 123 });

This code calls the 'get_user_profile' function in the database with user_id 123 and waits for the result.

Process Table

Step	Action	Input	Process	Output
1	Client calls supabase.rpc	{ user_id: 123 }	Send RPC request to Supabase	Request sent
2	Supabase receives request	RPC request	Parse function name and parameters	Function call prepared
3	Supabase calls DB function	Function: get_user_profile, Params: { user_id: 123 }	Execute function in Postgres	Function executes
4	Function runs in DB	user_id=123	Query user profile data	User profile data returned
5	Supabase receives result	User profile data	Package response	Response ready
6	Supabase sends response	Response ready	Send data back to client	Client receives data
7	Client receives data	User profile data	Process or display data	Data ready for use
8	End	N/A	No more steps	RPC call complete

💡 RPC call ends after client receives the function result.

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 4	After Step 6	Final
data	undefined	undefined	undefined	user profile object	user profile object	user profile object
error	undefined	undefined	undefined	null	null	null
user_id	undefined	123	123	123	123	123

Key Moments - 3 Insights

Why does the client wait after calling supabase.rpc?

Because supabase.rpc is asynchronous and waits for the database function to finish and return data, as shown in execution_table step 7.

What happens if the database function returns an error?

The error variable will hold the error details after step 4, and the client can check it to handle problems, as tracked in variable_tracker.

Is the function executed on the client or the database?

The function runs inside the database (step 4), not on the client, ensuring data security and performance.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the database function actually run?

A Step 4

B Step 3

C Step 5

D Step 6

💡 Hint

Check the 'Process' column where the function executes in Postgres.

According to variable_tracker, what is the value of 'data' after step 4?

A undefined

B user profile object

C null

D error object

💡 Hint

Look at the 'data' row under 'After Step 4' column.

If the client changes user_id to 456, what changes in the execution_table?

A Step 4 output changes to error

B Step 6 response is empty

C Step 3 input changes to user_id 456

D No changes at all

💡 Hint

Look at the 'Input' column in step 3 where parameters are passed.

Concept Snapshot

Calling functions via RPC in Supabase:
- Use supabase.rpc('function_name', {params}) to call DB functions.
- The call is asynchronous and returns data or error.
- The function runs securely inside the database.
- Client waits for the function result before continuing.
- Useful for complex queries or logic inside the DB.

Full Transcript

Calling functions via RPC in Supabase means the client sends a request to run a database function with parameters. Supabase receives this request, calls the function inside the Postgres database, and waits for the function to finish. The function executes the logic and returns data. Supabase then sends this data back to the client. The client receives the data and can use it. This process is asynchronous and secure because the function runs inside the database, not on the client. Variables like 'data' hold the result, and 'error' holds any problems. The flow ensures smooth communication between client and database for complex operations.

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