writing-migrations

name	writing-migrations
description	Generate Supabase SQL migrations at deploy time from the session branch diff. Used by simple-developer in the deploy-time migration round only.

Writing Migrations (deploy-time round)

You are simple-developer in migration mode. Your worktree is <WORKTREE_BASE>/simple on <SESSION_SHORT_ID>/simple, forked from session/<SESSION_SHORT_ID> (<WORKTREE_BASE> = /tmp/<$CLAUDE_PROJECT_DIR with every "/" replaced by "_">/<SESSION_ID>). Produce SQL migrations that make the real Supabase schema match what this session's app expects — nothing more.

1. Compute the session's net change

cd <WORKTREE_PATH>
git diff session-base/<SESSION_SHORT_ID>..session/<SESSION_SHORT_ID>

This is the branch's full diff since creation. Do NOT use git merge-base (it collapses after the first promotion). Do NOT diff against main (other sessions pollute it).

2. Identify schema-relevant changes

From that diff, keep only changes that imply a database schema change:

• Entity TypeScript types (e.g. src/**/types.ts, resource type defs).
• Fake-data generators that add/remove fields.
• dataProvider resource registrations (new resource = new table). Ignore CSS, component layout, copy, tests.

3. Compute the delta against what is already deployed

For each changed entity, compare the desired schema (from the TS types) with the schema already in supabase/migrations/ and supabase/schemas/. Emit ONLY the incremental delta. Anything already represented in supabase/migrations/ is already deployed — do not re-emit it. If the net diff has no schema impact, write nothing (a no-op deploy is valid) and report NO_MIGRATION_NEEDED.

4. Write idempotent SQL

Write to supabase/migrations/<YYYYMMDDHHMMSS>_<SESSION_SHORT_ID>_migration_<slug>.sql (timestamp via date -u +%Y%m%d%H%M%S). Use IF NOT EXISTS / IF EXISTS, correct column types matching the TS types, FKs, and RLS for new tables (RLS enabled + policies, never USING (true)).

5. View-recreation rule (BLOCKING correctness)

When a migration adds a column on a table referenced by a view in supabase/schemas/03_views.sql, recreate the view with CREATE OR REPLACE VIEW and place the new column as the very last item in the SELECT list — after every existing column AND after every existing computed AS alias (e.g. count(...) as nb_deals).

PostgreSQL forbids any ordinal shift in an existing view's SELECT list (error 42P16). "Between the raw columns and the computed aggregates" is still a shift — the aggregate's position increases by one. There are no exceptions. The mechanical rule is: positions 1..N of the new view must be identical to positions 1..N of the old view; the new column is position N+1.

Why not DROP VIEW … CASCADE; CREATE VIEW …? It silently drops dependent views/materialized views/rules, loses any explicit REVOKEs on the view (re-granted by default privileges at the next deploy without warning), and reads as a destructive operation in audit. Reserve it for cases CREATE OR REPLACE genuinely can't handle (column removal or rename). If you use it, enumerate dropped dependents in a SQL comment and re-create them in the same migration.

PostgREST queries the view, not the table — a missing update makes the column invisible to the app. The view's column order doesn't matter to API consumers (they address by name), so "append at end" has no API cost.

Example — adding importance to companies_summary (the view ends with count(...) as nb_deals, count(...) as nb_contacts):

create or replace view public.companies_summary with (security_invoker = on) as
select
    c.id, c.created_at, c.name, …, c.logo,
    count(distinct d.id) as nb_deals,
    count(distinct co.id) as nb_contacts,
    c.importance                              -- LAST, after every existing item
from public.companies c
    left join public.deals d on c.id = d.company_id
    left join public.contacts co on c.id = co.company_id
group by c.id;

Then update supabase/schemas/03_views.sql to the same order — the declarative schema must mirror the deployed view, including the chronological "append at end" placement of newer columns. Don't reorder the schema file to look prettier — schema drift breaks future supabase db diff generations.

6. Commit and hand off

Commit the SQL on <SESSION_SHORT_ID>/simple. Stop. SubagentStop hooks (typecheck/prettier/unit/e2e) run automatically. The orchestrator then sends you to quality-reviewer (migration mode) and the merger.

For Postgres correctness you may load Skill({skill: "supabase-postgres-best-practices"}).