Implementing Row-Based Permissions in Supabase Postgres

What Are Row-Based Permissions?

Row-based permissions—also called row-level security (RLS)—let you decide which individual rows in a table each user can read or modify. Instead of granting blanket access at the table or column level, you write policies that evaluate per-row predicates at query time. In Supabase, RLS is powered by the native PostgreSQL feature, but Supabase layers helpful defaults, session auth, and dashboard tooling on top.

Why Does This Matter?

Nearly every multi-tenant SaaS, analytics platform, or mobile app needs to isolate data between users or organizations. Hard-coding WHERE user_id = :current_user into every query is error-prone and brittle. RLS policies move that logic into the database where it is:

• Centralized — one source of truth, enforced on every access path (SQL, REST, GraphQL).
• Safer — impossible to bypass accidentally in app code.
• Auditable — policy definitions live in version-controlled migrations.
• Performant — evaluated by the PostgreSQL planner with indexed predicates.

How Supabase Implements RLS

Supabase stores an authenticated user’s JWT inside a PostgreSQL session variable via set_config('request.jwt.claims', ...). Inside your policy expressions you can reference claims such as auth.uid() or custom metadata. Once you ENABLE ROW LEVEL SECURITY on a table, PostgreSQL denies all access until at least one policy explicitly grants it.

Policy Life-Cycle

1. Create table and columns.
2. Enable RLS: ALTER TABLE projects ENABLE ROW LEVEL SECURITY;
3. Define policies with CREATE POLICY for each command (SELECT, INSERT, UPDATE, DELETE).
4. Test policies with different role and jwt headers using psql, Supabase Studio, or a SQL editor like Galaxy.

Step-by-Step Guide

1. Example Schema

CREATE TABLE projects (
id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
organization_id uuid REFERENCES organizations(id),
name text NOT NULL,
created_at timestamptz DEFAULT now(),
created_by uuid NOT NULL
);


2. Turn On RLS

ALTER TABLE projects ENABLE ROW LEVEL SECURITY;

3. Add a SELECT Policy

CREATE POLICY "Org members can read their projects"
ON projects
FOR SELECT
USING (organization_id IN (
SELECT organization_id
FROM memberships
WHERE user_id = auth.uid()
));


4. Add an INSERT Policy

CREATE POLICY "Org members can create projects"
ON projects
FOR INSERT WITH CHECK (
organization_id IN (
SELECT organization_id FROM memberships WHERE user_id = auth.uid())
AND created_by = auth.uid()
);


5. Add UPDATE/DELETE Policies (Optional)

You might allow only project owners to update or delete:

CREATE POLICY "Only creator can modify project"
ON projects
FOR UPDATE USING (created_by = auth.uid())
WITH CHECK (created_by = auth.uid());

CREATE POLICY "Only creator can delete project"
ON projects
FOR DELETE USING (created_by = auth.uid());


Best Practices

Principle of Least Privilege

Start with zero access: once ENABLE ROW LEVEL SECURITY is on, no one—including service_key users—can see rows unless a policy explicitly returns TRUE. Add precise policies one command at a time.

Use Database Roles for Admin-Override

Create a PostgreSQL role (e.g., db_admin) that is BYPASSRLS to run migrations, backfills, or analytics without policy interference.

Minimize Cross-Table Sub-queries

While legal, deeply nested sub-queries in policy predicates can hurt performance. Instead, pre-materialize membership relationships in join tables with proper indexes.

Source-Control Your Policies

Store all CREATE POLICY and ALTER TABLE ... RLS statements in migration files so staging and production stay identical.

Test in CI/CD

Write unit tests that connect as different roles and assert allowed/denied behavior. Tools like pgTAP or orval help automate this.

How Galaxy Helps

Because Galaxy is a modern SQL IDE with role switching and AI assistance, you can:

• Connect to Supabase in read-only or service role mode.
• Toggle roles inside a session (SET ROLE end_user;) to validate RLS policies without leaving the editor.
• Let the AI copilot generate CREATE POLICY statements with correct predicates based on your schema.
• Share endorsed test queries in Galaxy Collections so teammates know which scenarios pass.

RLS enforcement happens in Postgres, so all queries executed from Galaxy respect your policies automatically.

Practical Example

Imagine you run a bug-tracking SaaS where each customer (organization) must see only their tickets. The minimal set of policies:

ALTER TABLE tickets ENABLE ROW LEVEL SECURITY;

CREATE POLICY "Org can read their tickets" ON tickets
FOR SELECT USING (organization_id = auth.uid()::uuid);

CREATE POLICY "Org can file tickets" ON tickets
FOR INSERT WITH CHECK (organization_id = auth.uid()::uuid);


Because the policy predicate uses the implicit claim auth.uid(), your API, Realtime, and Edge Functions all inherit the same protections.

Common Misconceptions

"RLS is slow."

Policy predicates are compiled into the query plan. With proper indexes they incur negligible overhead.

"Supabase RLS only works through the REST API."

RLS is enforced at the database layer; psql, SQL editors, GraphQL, and REST all pass through the same gate.

"Using the service_role key is safer."

The service_role bypasses RLS entirely—great for server-side jobs, dangerous for client apps. Prefer anon or custom JWTs.

Troubleshooting Tips

• Unexpected 0 rows? Check pg_row_security view to see which policy blocked you.
• Policy never matches? Confirm auth.uid() returns the expected UUID in the session (select auth.uid();).
• Need to bulk update? Temporarily SET ROLE db_admin; or disable RLS in a transaction, then re-enable.

Conclusion

Row-based permissions in Supabase Postgres leverage PostgreSQL’s battle-tested RLS feature to deliver data isolation that is safe, performant, and centrally managed. By enabling RLS and crafting explicit policies you remove authorization logic from application code and gain a defense-in-depth posture. Tooling like Galaxy streamlines writing and auditing policies, but enforcement always lives in the database—exactly where it belongs.