Problem: Cannot dynamically set database connection for Supabase Preview Branches

[Nciso]

Problem

When using Supabase Preview Branches, each preview branch has its own database URL. Currently, EDGE_WORKER_DB_URL must be set as a static environment variable, which prevents connecting to the correct preview branch database dynamically.

This is only a problem for preview branches - production/main branch works fine! ✨

What I Want to Do

I want to derive the pooler connection string from SUPABASE_DB_URL (which is already available and branch-aware):

const directUrl = Deno.env.get('SUPABASE_DB_URL');
const poolerUrl = directUrl.replace(':5432/', ':6543/');

EdgeWorker.startFlowWorker(MyFlow, {
  connectionString: poolerUrl, // ❌ Currently doesn't work
});

Why It Doesn't Work

SupabasePlatformAdapter requires EDGE_WORKER_DB_URL as a mandatory environment variable during initialization:

// pkgs/edge-worker/src/platform/SupabasePlatformAdapter.ts
const required = [
  'EDGE_WORKER_DB_URL',  // ❌ Always required
  // ...
];

Even if I provide connectionString in the worker config:

1. The adapter still requires the env var
2. context.sql in handlers uses the env var connection, not the config one

The Solution I'm Hoping For

Make EDGE_WORKER_DB_URL optional when connectionString is provided in config, or auto-derive it from SUPABASE_DB_URL.

Priority:

1. connectionString in worker config (explicit override)
2. EDGE_WORKER_DB_URL env var (backwards compatibility)
3. Auto-derive from SUPABASE_DB_URL → convert :5432/ to :6543/

This way preview branches can automatically connect to their branch-specific database!

Why This Matters

• Can't pre-configure env vars for every preview branch
• SUPABASE_DB_URL is already available and branch-aware
• Just need to convert it to pooler format (:5432/ → :6543/)

Current workaround: Manually set EDGE_WORKER_DB_URL per branch, which doesn't scale.

Related Files

• pkgs/edge-worker/src/platform/SupabasePlatformAdapter.ts - Validation logic
• pkgs/edge-worker/src/EdgeWorker.ts - Worker startup
• pkgs/edge-worker/src/core/workerConfigTypes.ts - Already documents connectionString option

Current workaround: I'm manually setting the env variable after preview creation, but it would be great if this could work automatically. I'd be happy to help with the implementation if needed!

Thanks! 🙏

[jumski]

Hey @enciso, sorry for the delayed response! I replied in the Discord thread a while back but then completely forgot to follow up here with actual details.

Good news: You found a real bug! The connectionString option is documented but doesn't actually work for handler context - only the env var gets used. I'll be fixing this.

However, the auto-derivation approach won't work because the URLs are fundamentally different:

Direct:  postgres://postgres:[pass]@db.{ref}.supabase.co:5432/postgres
Pooler:  postgres://postgres.{ref}:[pass]@aws-1-{region}.pooler.supabase.com:6543/postgres

It's not just a port change - the hostname, username format, AND region all differ.

From the direct URL you can extract:

• Project ref - yes
• Password - yes
• Region - no

The region (e.g., us-east-1, eu-central-1) isn't present in SUPABASE_DB_URL or any other standard Supabase env var. So even if you rebuilt the URL format correctly, you'd have no way to know if it should be aws-0-us-east-1.pooler.supabase.com or aws-0-eu-central-1.pooler.supabase.com.

Why transaction pooler is required:

EdgeWorker needs pooled connections because Edge Functions can be killed at any time. Direct connections would be left hanging, exhausting your connection pool quickly.

The fix:

Once I fix the connectionString bug, you'll be able to:

EdgeWorker.start(MyFlow, {
  connectionString: Deno.env.get('MY_CUSTOM_POOLER_URL'),
});

For preview branches:

Unfortunately, you'll need to get the pooler URL from each preview branch's dashboard (Settings -> Database -> Connection string -> Transaction pooler) and set it as an env var. There's no way to auto-derive it.

Risky alternative: Once the bug is fixed, you could technically use SUPABASE_DB_URL directly:

EdgeWorker.start(MyFlow, {
  connectionString: Deno.env.get('SUPABASE_DB_URL'),
});

But I strongly advise against this - direct connections from serverless workers can quickly exhaust your connection pool, and I can't provide support for issues arising from this approach. The transaction pooler exists for good reason.

Would you be able to test the fix once it's ready?

[jumski]

Update: I checked with the Supabase team - exposing the pooler URL or database region is a known gap they've discussed internally. For now, manually setting the pooler URL is the only option, but it's on their radar.