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Database Migrations Guide

Migrations are version-controlled changes to your database schema. This guide walks through creating, testing, and deploying migrations in the FindU ecosystem.

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Migration Workflow Overview

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Creating Your First Migration

1

Set up your environment

# Ensure you're in dev environment
./findu env switch dev

# Navigate to supabase directory
cd supabase
2

Create a feature branch

git checkout dev
git pull origin dev
git checkout -b feature/add-user-preferences
3

Generate migration file

supabase migration new add_user_preferences_table
This creates a timestamped file in supabase/migrations/:
20240205123456_add_user_preferences_table.sql
4

Write your migration

Edit the generated file with your SQL:
-- Create user preferences table
CREATE TABLE IF NOT EXISTS public.user_preferences (
  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
  student_id uuid NOT NULL REFERENCES public.students(id) ON DELETE CASCADE,
  theme text DEFAULT 'light' CHECK (theme IN ('light', 'dark', 'auto')),
  notifications_enabled boolean DEFAULT true,
  created_at timestamptz DEFAULT now(),
  updated_at timestamptz DEFAULT now()
);

-- Add RLS policies
ALTER TABLE public.user_preferences ENABLE ROW LEVEL SECURITY;

-- Students can only see their own preferences
CREATE POLICY "Students can view own preferences" 
  ON public.user_preferences FOR SELECT
  USING (auth.uid() IN (
    SELECT user_id FROM public.profiles WHERE student_id = user_preferences.student_id
  ));

-- Students can update their own preferences
CREATE POLICY "Students can update own preferences"
  ON public.user_preferences FOR UPDATE
  USING (auth.uid() IN (
    SELECT user_id FROM public.profiles WHERE student_id = user_preferences.student_id
  ));

-- Create updated_at trigger
CREATE TRIGGER update_user_preferences_updated_at
  BEFORE UPDATE ON public.user_preferences
  FOR EACH ROW
  EXECUTE FUNCTION update_updated_at_column();
5

Test locally

# Reset local database (applies all migrations)
supabase db reset

# Verify your changes
supabase db diff
6

Commit and push

git add .
git commit -m "feat: add user preferences table with RLS"
git push origin feature/add-user-preferences
7

Create pull request

gh pr create --base dev --title "Add user preferences table" \
  --body "Adds table for storing user theme and notification preferences"

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Types of Migrations

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Schema Migrations

-- Always use IF NOT EXISTS for safety
CREATE TABLE IF NOT EXISTS public.feature_flags (
  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
  name text NOT NULL UNIQUE,
  enabled boolean DEFAULT false,
  rollout_percentage integer DEFAULT 0 CHECK (rollout_percentage BETWEEN 0 AND 100),
  created_at timestamptz DEFAULT now()
);

-- Always add RLS
ALTER TABLE public.feature_flags ENABLE ROW LEVEL SECURITY;

-- Add appropriate indexes
CREATE INDEX idx_feature_flags_name ON public.feature_flags(name);

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Data Migrations

Data migrations should be idempotent - running them multiple times should have the same result.
-- Example: Backfill data with proper checks
UPDATE public.students 
SET areas_of_interest = ARRAY['undecided']
WHERE areas_of_interest IS NULL 
  OR array_length(areas_of_interest, 1) = 0;

-- Example: Migrate data between tables
INSERT INTO public.user_preferences (student_id, theme, notifications_enabled)
SELECT 
  id as student_id,
  COALESCE(settings->>'theme', 'light') as theme,
  COALESCE((settings->>'notifications')::boolean, true) as notifications_enabled
FROM public.students
WHERE NOT EXISTS (
  SELECT 1 FROM public.user_preferences WHERE student_id = students.id
);

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Creating Functions

-- Utility function for updated_at timestamps
CREATE OR REPLACE FUNCTION update_updated_at_column()
RETURNS TRIGGER AS $$
BEGIN
  NEW.updated_at = now();
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

-- Domain-specific function
CREATE OR REPLACE FUNCTION calculate_match_score(
  student_id uuid,
  school_id uuid
) RETURNS numeric AS $$
DECLARE
  score numeric;
BEGIN
  -- Your matching logic here
  SELECT 
    CASE 
      WHEN s.gpa >= sch.min_gpa THEN 0.25
      ELSE 0
    END +
    -- Add more scoring logic
    0.5 -- Base score
  INTO score
  FROM public.students s, public.schools sch
  WHERE s.id = student_id AND sch.id = school_id;
  
  RETURN COALESCE(score, 0);
END;
$$ LANGUAGE plpgsql;

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Testing Migrations

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Local Testing Checklist

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Writing Rollback Migrations

For risky changes, prepare a rollback migration: 
-- Migration: 20240205123456_add_complex_feature.sql
-- Rollback: 20240205123457_rollback_complex_feature.sql

-- Drop new constraints
ALTER TABLE public.students DROP CONSTRAINT IF EXISTS check_gpa;

-- Drop new columns
ALTER TABLE public.students DROP COLUMN IF EXISTS new_feature;

-- Drop new tables
DROP TABLE IF EXISTS public.user_preferences CASCADE;

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Deployment Process

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To Development

  1. Automatic: Merging PR to dev branch triggers deployment
  2. Manual: If needed, run supabase db push after switching to dev

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To Production

  1. Create PR: From dev to main branch
  2. Review Required: Another developer must approve
  3. Automatic Deploy: Merging triggers production deployment
  4. Monitor: Check Supabase dashboard for any issues

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Best Practices

Always Include RLS

Every table should have Row Level Security enabled and appropriate policies

Make Migrations Idempotent

Use IF NOT EXISTS, IF EXISTS, and proper checks

One Concern Per Migration

Keep migrations focused on a single feature or change

Test Thoroughly

Always run supabase db reset before pushing

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Common Patterns

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Adding Audit Fields

-- Standard audit fields for new tables
created_at timestamptz DEFAULT now(),
updated_at timestamptz DEFAULT now(),
created_by uuid REFERENCES auth.users(id),
updated_by uuid REFERENCES auth.users(id)

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Setting Up RLS

-- Enable RLS
ALTER TABLE public.table_name ENABLE ROW LEVEL SECURITY;

-- Public read access
CREATE POLICY "Public can view" ON public.table_name
  FOR SELECT USING (true);

-- Authenticated write access
CREATE POLICY "Authenticated can insert" ON public.table_name
  FOR INSERT WITH CHECK (auth.role() = 'authenticated');

-- Owner-only access
CREATE POLICY "Users can manage own records" ON public.table_name
  FOR ALL USING (auth.uid() = user_id);

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Performance Indexes

-- Foreign key indexes (often missed)
CREATE INDEX idx_table_foreign_key ON public.table_name(foreign_key_id);

-- Timestamp indexes for queries
CREATE INDEX idx_table_created_at ON public.table_name(created_at DESC);

-- Text search indexes
CREATE INDEX idx_table_search ON public.table_name USING gin(to_tsvector('english', name || ' ' || description));

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Troubleshooting

Next, learn about schema management or data operations.