ADR-0020: Single business database (drop martin / erd dual DB)

• Status: Accepted (2026-08-03)
• Decision makers: Project maintainers

Context

Application long used two DBs on same MySQL instance: martin (system/auth) and erd (modeling metadata), dual Hikari + SqlSessionFactory routed by mapper package. Railway / remote plugin MySQL defaults one DB name (often railway); dual DB creation and db/init seeding became deployment main pain.

Historical comment said sys_user / sys_role name collision prevents merge. Audit result:

Source	Conflicting tables	Conclusion
martin	Full sys_user / sys_role (auth source of truth)	Keep
Old erd dump	Same-name stub tables (id/username/password only)	Zero erd mapper references, discard on merge

No other table name overlap; can coexist same DB.

Decision

1. Physically single DB: default name erd (env MYSQLDATABASE; no DB_ERD / DB_MARTIN / DB_NAME fallback).
2. db/init schema only: 01_create_database.sql + 02_tables.sql (CREATE TABLE); no seeds, demo, privileges scripts.
3. Seeds in Flyway: backend/.../db/migration/erd/ V3+ (system baseline / new user permissions / public demo / E2E accounts); backend startup runs via ErdFlywayConfig.
4. Transition keeps dual SqlSessionFactory: martinDataSource and erdDataSource still separated by package scan, but JDBC URL points to same MYSQLDATABASE, credentials same MYSQLUSER / MYSQLPASSWORD (avoid mapper explosion this round). Single DS merge can be future ADR.
5. Env vars: Spring reads Railway plugin native names directly (MYSQLHOST / MYSQLPORT / MYSQLDATABASE / MYSQLUSER / MYSQLPASSWORD), each single placeholder, no nested fallback. Compose: MySQL container official MYSQL_DATABASE / MYSQL_USER / MYSQL_PASSWORD, backend injects same MYSQL*.

Consequences

• Railway: Link MySQL injects MYSQL*; create one DB + import schema; Redeploy then Flyway seeds. No longer require DB_MARTIN≠DB_ERD two DBs, nor DB_* Variable Reference.
• Local existing dual DB data volume: must rebuild volume (docker compose down -v then up) or manually migrate martin.* tables into erd and set MYSQLDATABASE=erd.
• Production existing dual DB data: export both sides → import single business DB (discard erd stub sys_*) → MYSQLDATABASE points there → confirm flyway_schema_history then baseline / run missing versions as needed.
• E2E seeds enter DB via Flyway; public login still rejected by erd.security.e2e-accounts-enabled=false.

Verification

• mvn -q -DskipTests compile
• ./scripts/railway-mysql-init.sh --dry-run lists only 01+02
• Empty volume compose first start backend Flyway ≥ V6; SELECT COUNT(*) FROM erd.sys_user > 0