Seed data management in Supabase - Mini Project: Build & Apply

Seed Data Management with Supabase

📖 Scenario: You are setting up a new Supabase project for a small online bookstore. To get started, you need to add some initial books data into your database so the app can display books right away.

🎯 Goal: Create seed data for the books table in Supabase, configure a helper variable for batch insertion, write the main logic to insert the seed data, and finalize the seed script for deployment.

📋 What You'll Learn

Create a list of book records with exact fields and values

Add a configuration variable for batch size

Write the insertion logic using Supabase client

Complete the seed script with proper export and async function

💡 Why This Matters

🌍 Real World

Seeding initial data is a common step when setting up new cloud databases to have ready-to-use content for development or demos.

💼 Career

Knowing how to manage seed data with Supabase is useful for backend developers and cloud engineers working with modern serverless databases.

1

Create the initial seed data array

Create a constant called books that is an array of objects. Each object must have these exact fields and values:
{ id: 1, title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
{ id: 2, title: '1984', author: 'George Orwell', year: 1949 },
and { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee', year: 1960 }.

Supabase

# Your code here

Hint

Use const books = [ ... ] and include exactly three objects with the given fields and values.

2

Add a batch size configuration variable

Create a constant called BATCH_SIZE and set it to 3 to control how many records to insert at once.

Supabase

const books = [
  { id: 1, title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
  { id: 2, title: '1984', author: 'George Orwell', year: 1949 },
  { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee', year: 1960 }
];

# Your code here

Hint

Use const BATCH_SIZE = 3; exactly as shown.

3

Write the seed insertion logic

Write an async function called seedBooks that uses the Supabase client supabase to insert the books array into the books table using supabase.from('books').insert(books). Await the insertion call.

Supabase

const books = [
  { id: 1, title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
  { id: 2, title: '1984', author: 'George Orwell', year: 1949 },
  { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee', year: 1960 }
];

const BATCH_SIZE = 3;

# Your code here

Hint

Define async function seedBooks() and inside it call await supabase.from('books').insert(books);

4

Complete the seed script for deployment

Export the seedBooks function as the default export using export default seedBooks;.

Supabase

const books = [
  { id: 1, title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
  { id: 2, title: '1984', author: 'George Orwell', year: 1949 },
  { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee', year: 1960 }
];

const BATCH_SIZE = 3;

async function seedBooks() {
  await supabase.from('books').insert(books);
}

# Your code here

Hint

Use export default seedBooks; exactly as shown to complete the seed script.

Practice

1. What is the main purpose of seed data in a Supabase project?

easy

A. To delete all existing data from the database

B. To backup the database before changes

C. To add initial data automatically to the database

D. To monitor database performance

Solution

1. Step 1: Understand seed data concept

   Seed data is used to populate the database with initial or default data automatically.

2. Step 2: Identify the purpose in Supabase

   In Supabase, seed data helps set up consistent data for testing and development.

3. Final Answer:

   To add initial data automatically to the database -> Option C

4. Quick Check:

   Seed data = initial data setup [OK]

Hint: Seed data means initial data added automatically [OK]

Common Mistakes:

• Confusing seed data with backup or monitoring
• Thinking seed deletes data instead of adding
• Assuming seed data is for performance tuning

2. Which command runs seed scripts in a Supabase project?

easy

A. supabase db backup create

B. supabase db migrate run

C. supabase db reset

D. supabase db seed run

Solution

1. Step 1: Recall Supabase seed command

   The command to execute seed scripts is supabase db seed run.

2. Step 2: Differentiate from other commands

   supabase db migrate run applies migrations, not seeds; reset and backup are unrelated.

3. Final Answer:

   supabase db seed run -> Option D

4. Quick Check:

   Seed scripts run with supabase db seed run [OK]

Hint: Seed scripts run with 'supabase db seed run' command [OK]

Common Mistakes:

• Using migrate command instead of seed
• Confusing reset with seed run
• Trying backup commands for seeding

3. Given this seed script snippet in Supabase:

INSERT INTO users (id, name) VALUES (1, 'Alice'), (2, 'Bob');
INSERT INTO users (id, name) VALUES (3, 'Charlie');

What will be the total number of users after running the seed?

medium

A. 3

B. 2

C. 1

D. 4

Solution

1. Step 1: Count inserted rows in first statement

   The first INSERT adds 2 users: Alice and Bob.

2. Step 2: Count inserted rows in second statement

   The second INSERT adds 1 user: Charlie.

3. Step 3: Calculate total users inserted

   Total users = 2 + 1 = 3.

4. Final Answer:

   3 -> Option A

5. Quick Check:

   2 + 1 = 3 users inserted [OK]

Hint: Add all inserted rows to find total users [OK]

Common Mistakes:

• Counting only first INSERT statement
• Assuming duplicate rows overwrite
• Miscounting number of values per INSERT

4. You run supabase db seed run but get an error: duplicate key value violates unique constraint. What is the likely cause?

medium

A. Database connection is lost

B. Seed script tries to insert data with existing primary keys

C. Supabase CLI is not installed

D. Seed script syntax is incorrect

Solution

1. Step 1: Understand the error message

   The error means the seed script tries to insert rows with keys already in the database.

2. Step 2: Identify cause in seed data context

   Duplicate primary keys cause conflicts when inserting seed data multiple times without cleanup.

3. Final Answer:

   Seed script tries to insert data with existing primary keys -> Option B

4. Quick Check:

   Duplicate key error = duplicate primary keys in seed [OK]

Hint: Duplicate key error means repeated primary keys in seed data [OK]

Common Mistakes:

• Assuming syntax error causes duplicate key message
• Blaming CLI installation for data errors
• Ignoring database state before seeding

5. You want to seed a Supabase database with initial users but avoid duplicate entries if the seed runs multiple times. Which approach is best?

hard

A. Use INSERT ... ON CONFLICT DO NOTHING in seed scripts

B. Delete the entire database before each seed run

C. Run seed scripts only once manually

D. Use DROP TABLE users before inserting

Solution

1. Step 1: Understand the problem of duplicates

   Running seed multiple times can cause duplicate key errors if data already exists.

2. Step 2: Choose a safe insert method

   Using INSERT ... ON CONFLICT DO NOTHING skips inserting duplicates safely.

3. Step 3: Evaluate other options

   Deleting database or tables is risky and inefficient; running seed once is error-prone.

4. Final Answer:

   Use INSERT ... ON CONFLICT DO NOTHING in seed scripts -> Option A

5. Quick Check:

   Safe inserts prevent duplicates with ON CONFLICT [OK]

Hint: Use ON CONFLICT DO NOTHING to avoid duplicate inserts [OK]

Common Mistakes:

• Dropping tables can cause data loss
• Assuming seed runs only once always
• Deleting whole database is overkill