A SaaS application may serve hundreds or thousands of companies from one platform.
Each company is a tenant.
The challenge is simple to describe:
Company A should never see Company B's data.
The Tenant Model
A common structure is:
organizations
users
projects
records
Each user belongs to an organization.
Application records can then reference an organization ID.
For example:
projects
---------
id
organization_id
name
Why Tenant IDs Matter
The organization_id becomes part of your data model.
Queries can then be scoped to the current organization.
Current organization
↓
organization_id
↓
Application records
Protecting Tenant Data
RLS can enforce tenant boundaries.
A policy can allow users to access rows only when the row belongs to an organization they are authorized to access.
Team Members
One organization may contain multiple users.
For example:
Acme Inc.
├── Owner
├── Manager
└── Employee
Roles can control what each member can do.
Avoid Trusting Client-Supplied IDs
Do not blindly trust an organization_id sent from the browser.
The server and database should determine whether the authenticated user actually belongs to that organization.
Testing Tenant Isolation
Always test:
Tenant A → Tenant A data
Tenant A → Tenant B data
Tenant B → Tenant A data
Cross-tenant access should be blocked.
Scaling
A shared database can work well for many SaaS applications.
For larger or more sensitive workloads, you may eventually consider stronger isolation strategies.
Final Thoughts
Multi-tenancy starts with data modeling.
Define organizations clearly, associate records with tenants and enforce those boundaries at the database level.
Supabase and PostgreSQL provide the building blocks needed for this architecture.