Supabase Database Seeding Skill

Supabase Database Seeding

Proper patterns for seeding data in Supabase projects that work locally and in production.

Key Principle: Separate Schema from Data

Critical: Keep schema (tables, functions) in migrations, data in seed files.

| File Type | Contains | When Applied | |-----------|----------|--------------| | migrations/*.sql | Tables, functions, triggers, RLS policies | db push, db reset | | seed.sql | INSERT statements, backfill logic | db reset, db push --include-seed |

Setup

1. Configure seed.sql in config.toml

[db.seed]
enabled = true
sql_paths = ["./seed.sql"]

2. Create seed.sql

Location: supabase/seed.sql (same level as migrations/)

Seed File Patterns

Pattern 1: Simple Data Seeding

For basic reference data:

-- Seed: Reference Data
-- Description: Seeds initial reference data
-- Run: npx supabase db reset (local) or npx supabase db push --include-seed (production)

-- Use ON CONFLICT for idempotency (can run multiple times safely)
INSERT INTO public.categories (name, slug)
VALUES
  ('Technology', 'technology'),
  ('Science', 'science'),
  ('Arts', 'arts')
ON CONFLICT (slug) DO UPDATE SET
  name = EXCLUDED.name;

Pattern 2: User-Dependent Seeding

When data depends on auth.users (which doesn't exist until signup):

Step 1: Create config table in migration

-- Migration: Create seed config infrastructure
CREATE TABLE IF NOT EXISTS public.seed_config (
  email TEXT PRIMARY KEY,
  config JSONB NOT NULL,
  created_at TIMESTAMPTZ DEFAULT NOW()
);

Step 2: Create deferred setup function in migration

CREATE OR REPLACE FUNCTION public.apply_seed_config(p_user_id UUID, p_email TEXT)
RETURNS BOOLEAN
LANGUAGE plpgsql
SECURITY DEFINER SET search_path = ''
AS $$
DECLARE
  v_config JSONB;
BEGIN
  SELECT config INTO v_config FROM public.seed_config WHERE email = p_email;
  IF v_config IS NULL THEN RETURN FALSE; END IF;

  -- Apply configuration to user (customize per project)
  UPDATE public.profiles
  SET role = v_config->>'role'
  WHERE id = p_user_id;

  RETURN TRUE;
END;
$$;

Step 3: Hook into handle_new_user trigger in migration

CREATE OR REPLACE FUNCTION public.handle_new_user()
RETURNS TRIGGER
LANGUAGE plpgsql
SECURITY DEFINER SET search_path = ''
AS $$
BEGIN
  INSERT INTO public.profiles (id, email) VALUES (NEW.id, NEW.email);
  PERFORM public.apply_seed_config(NEW.id, NEW.email);
  RETURN NEW;
END;
$$;

Step 4: Seed the configuration data

-- seed.sql
INSERT INTO public.seed_config (email, config)
VALUES ('admin@example.com', '{"role": "admin"}'::jsonb)
ON CONFLICT (email) DO UPDATE SET config = EXCLUDED.config;

-- Backfill for existing users
DO $$
DECLARE v_user RECORD;
BEGIN
  FOR v_user IN SELECT id, email FROM auth.users LOOP
    PERFORM public.apply_seed_config(v_user.id, v_user.email);
  END LOOP;
END $$;

Pattern 3: Domain-Based Seeding

Auto-add users by email domain:

-- Migration: Domain config table
CREATE TABLE public.domain_config (
  domain TEXT PRIMARY KEY,
  config JSONB NOT NULL
);

CREATE OR REPLACE FUNCTION public.apply_domain_config(p_user_id UUID, p_email TEXT)
RETURNS BOOLEAN
LANGUAGE plpgsql
SECURITY DEFINER SET search_path = ''
AS $$
DECLARE
  v_domain TEXT := split_part(p_email, '@', 2);
  v_config JSONB;
BEGIN
  SELECT config INTO v_config FROM public.domain_config WHERE domain = v_domain;
  IF v_config IS NULL THEN RETURN FALSE; END IF;
  -- Apply domain-based configuration
  RETURN TRUE;
END;
$$;

-- seed.sql
INSERT INTO public.domain_config (domain, config)
VALUES
  ('company.com', '{"role": "employee"}'::jsonb),
  ('partner.com', '{"role": "partner"}'::jsonb)
ON CONFLICT (domain) DO UPDATE SET config = EXCLUDED.config;

Commands

Local Development

# Apply migrations only
npx supabase db push --local

# Apply migrations + seed
npx supabase db push --local --include-seed

# Full reset (DESTROYS DATA) + apply migrations + seed
npx supabase db reset

Production

# Apply migrations only (safe)
npx supabase db push --project-id YOUR_PROJECT_ID

# Apply migrations + seed (careful!)
npx supabase db push --project-id YOUR_PROJECT_ID --include-seed

Best Practices

1. Always Use ON CONFLICT

-- CORRECT - Idempotent
INSERT INTO categories (slug, name) VALUES ('tech', 'Technology')
ON CONFLICT (slug) DO UPDATE SET name = EXCLUDED.name;

-- WRONG - Fails on re-run
INSERT INTO categories (slug, name) VALUES ('tech', 'Technology');

2. Use DO Blocks for Complex Logic

DO $$
DECLARE
  v_record RECORD;
BEGIN
  FOR v_record IN SELECT * FROM some_table LOOP
    -- Complex logic here
  END LOOP;
END $$;

3. Comment Your Seeds

-- Seed: Admin Users Configuration
-- Description: Sets up admin users for new signups
-- Dependencies: migrations/20240101_create_profiles.sql
-- Run: npx supabase db push --include-seed

4. Keep Seeds Idempotent

Seeds may run multiple times. Design them to be re-runnable without errors.

5. Separate Concerns

Config data → seed.sql (emails, domains, settings)
Schema → migrations (tables, functions)
Backfill logic → DO blocks in seed.sql

Common Mistakes

Mistake 1: Tables in Seed Files

-- WRONG - Tables belong in migrations
CREATE TABLE IF NOT EXISTS public.users (...);
INSERT INTO public.users ...;

Mistake 2: No Conflict Handling

-- WRONG - Will fail if data exists
INSERT INTO settings (key, value) VALUES ('theme', 'dark');

-- CORRECT
INSERT INTO settings (key, value) VALUES ('theme', 'dark')
ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value;

Mistake 3: Assuming Users Exist

-- WRONG - auth.users may be empty
INSERT INTO profiles SELECT id FROM auth.users;

-- CORRECT - Use deferred pattern with triggers

File Structure

supabase/
├── config.toml          # [db.seed] configuration
├── seed.sql             # Data seeding
└── migrations/
    ├── 001_initial.sql
    └── 002_seed_config.sql  # Seed infrastructure

For the complete deferred seeding pattern, see deferred-seeding.md.

Agent Skills: Supabase Database Seeding

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