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Introduction
Most multi-tenant Spring apps filter by tenant_id in every query:
SELECT * FROM orders WHERE tenant_id = :tenantId;
It works — until it doesn’t. One missing predicate in a new query, an ad-hoc export, or a junior’s quick fix, and you’ve leaked one customer’s data to another.
There’s a safer way: let the database enforce tenancy for you. PostgreSQL’s Row-Level Security (RLS) can make every table automatically filter by the current tenant, so even a forgotten WHERE clause can’t escape the fence.
In this article you’ll wire Postgres RLS + Spring Boot 3 to:
Isolate each tenant by default (no code changes per query)
Support admins who can read across tenants
Pass the tenant from the HTTP request → JDBC safely through the pool
Keep integration tests simple and fast
Everything here is copy-paste ready and framework-light.
