database（数据库）

Database & Data Modeling

Every SaaS app needs a database, and the schema decisions you make early are expensive to change later. This skill helps you choose the right database, design a clean schema, and set up security — explained without jargon.

Core Principles

• Choose the database that matches your hosting platform. Don't fight the defaults.
• Schema design is product design. Get the relationships right early — migrations are painful later.
• Every SaaS app is multi-tenant. Every table needs a way to isolate customer data.
• Start simple. You don't need Redis, Elasticsearch, or a data warehouse at $0-10k MRR.
• Row Level Security is not optional. One leaked customer seeing another's data kills trust.

Choosing a Database

For Most Solo Founders: Use What Your Platform Gives You

The short answer: Use Supabase (PostgreSQL) unless you have a specific reason not to. It gives you database + auth + storage + realtime + Row Level Security in one service.

When You Might Need Something Else

Schema Design for SaaS

The Three Tables Every SaaS Needs

-- 1. Users (who uses the app)
create table users (
  id uuid primary key default gen_random_uuid(),
  email text unique not null,
  full_name text,
  avatar_url text,
  created_at timestamptz default now(),
  updated_at timestamptz default now()
);

-- 2. Organizations / Teams (multi-tenancy)
create table organizations (
  id uuid primary key default gen_random_uuid(),
  name text not null,
  slug text unique not null,
  plan text default 'free',
  stripe_customer_id text,
  created_at timestamptz default now(),
  updated_at timestamptz default now()
);

-- 3. Memberships (who belongs to which org)
create table memberships (
  id uuid primary key default gen_random_uuid(),
  user_id uuid references users(id) on delete cascade,
  org_id uuid references organizations(id) on delete cascade,
  role text default 'member' check (role in ('owner', 'admin', 'member')),
  created_at timestamptz default now(),
  unique(user_id, org_id)
);

Adding Your Core Business Object

Every SaaS has a "main thing" — projects, campaigns, invoices, etc. Connect it to the org:

create table [your_core_object] (
  id uuid primary key default gen_random_uuid(),
  org_id uuid references organizations(id) on delete cascade not null,
  created_by uuid references users(id),
  -- your fields here
  name text not null,
  status text default 'active',
  created_at timestamptz default now(),
  updated_at timestamptz default now()
);

-- Always index the org_id for multi-tenant queries
create index idx_[object]_org_id on [your_core_object](org_id);

Tell AI:

Design a database schema for [describe your SaaS product].
The main objects are: [list your core objects].
Users belong to organizations. Each org has its own data.
Use Supabase (PostgreSQL). Include:
- Table definitions with proper types and constraints
- Foreign key relationships
- Indexes for common queries
- Row Level Security policies

Row Level Security (RLS)

RLS ensures users can only see their own organization's data. This is critical for SaaS.

Basic Pattern

-- Enable RLS on every table with customer data
alter table [your_table] enable row level security;

-- Users can only see rows belonging to their org
create policy "Users see own org data"
  on [your_table]
  for select
  using (
    org_id in (
      select org_id from memberships
      where user_id = auth.uid()
    )
  );

-- Users can only insert into their own org
create policy "Users insert own org data"
  on [your_table]
  for insert
  with check (
    org_id in (
      select org_id from memberships
      where user_id = auth.uid()
    )
  );

RLS Checklist

For every table that contains customer data:
- [ ] RLS is enabled
- [ ] SELECT policy restricts to user's org
- [ ] INSERT policy restricts to user's org
- [ ] UPDATE policy restricts to user's org
- [ ] DELETE policy restricts to user's org (or is blocked)
- [ ] Tested: User A cannot see User B's data

Migrations

What Migrations Are

Database migrations are version-controlled changes to your schema. Like git for your database structure.

Best Practices

• Never edit production tables directly. Always use a migration.
• Each migration does one thing. "Add status column to projects" not "Restructure everything."
• Migrations are forward-only. Don't delete old migrations. Add new ones.
• Test on a branch database first. Supabase has database branching for this.

Tell AI:

Write a Supabase migration to [describe the change].
Current table structure: [describe or paste current schema].
Include: the SQL migration and any RLS policy updates needed.

Common Patterns

Soft Deletes

Don't hard-delete records. Mark them as deleted:

alter table [table] add column deleted_at timestamptz;

-- Update RLS to exclude soft-deleted rows
create policy "Hide deleted rows"
  on [table] for select
  using (deleted_at is null and org_id in (...));

Audit Trail

Track who changed what:

create table audit_log (
  id uuid primary key default gen_random_uuid(),
  org_id uuid references organizations(id),
  user_id uuid references users(id),
  action text not null, -- 'create', 'update', 'delete'
  table_name text not null,
  record_id uuid not null,
  changes jsonb,
  created_at timestamptz default now()
);

Status Workflows

-- Use a check constraint for valid statuses
status text default 'draft' check (
  status in ('draft', 'active', 'paused', 'completed', 'archived')
)

Performance Basics

Index Rules

• Always index foreign keys (org_id, user_id, etc.)
• Index columns you filter or sort by frequently
• Don't index everything — each index slows down writes

Query Tips

• Select only the columns you need, not SELECT *
• Use pagination for lists (LIMIT/OFFSET or cursor-based)
• Use database views for complex repeated queries
• Add explain analyze before queries to check performance

Common Mistakes

Success Looks Like

• Clean schema with clear relationships between tables
• RLS policies on every customer-facing table, tested
• Migrations tracked and versioned
• Queries are fast for your current scale
• You can explain your data model to a contractor or AI tool clearly

Related Skills

• compliance — Encryption and audit trail requirements for regulated industries
• deploy — Get your app and database live in production
• secure — Security beyond RLS: auth, API protection, data encryption
• build — Hand your schema to AI tools and build features on top of it
• payments — Add Stripe tables and subscription tracking to your schema