tasks/CROSS2_schema_evolution/analysis_guidance.md

Analysis Guidance — CROSS2_schema_evolution

Tools to run

• cat service_a/migrations/002_add_columns.py — CRITICAL: shows all schema changes
• cat service_a/config.py — read default values for backfill
• cat shared/schema.sql — expected final schema
• cat service_b/models.py — compare with migration to find staleness
• grep -n "SELECT \*" service_b/queries.py — find unsafe queries

Key Findings

Schema changes (from migration 002):

1. Column RENAMED: user_name → username (breaking change)
2. Column ADDED: email_verified (boolean, default: False)
3. Column ADDED: last_login_at (datetime, default: None)
4. Column ADDED: account_tier (string, default: from config DEFAULT_TIER)

Service B staleness:

• service_b/models.py User class still has user_name attribute (wrong)
• service_b/models.py missing email_verified, last_login_at, account_tier fields
• service_b/queries.py has 2 queries using SELECT * — will break with new columns

Backfill defaults (from service_a/config.py):

• email_verified: False
• last_login_at: None
• account_tier: DEFAULT_TIER constant (read its value from config.py)

Tell Executor

1. In service_b/models.py: rename user_name → username, add 3 new fields
2. In service_b/queries.py: replace both SELECT * with explicit column lists
3. In scripts/backfill.py: UPDATE all existing rows setting the 3 new columns to defaults