Ecto Essentials

RULES — Follow these with no exceptions

1. Always use changesets for inserts and updates — never pass raw maps to Repo
2. Preload associations before accessing them — avoid N+1 queries
3. Use transactions for multi-step operations that must succeed together
4. Add database constraints (unique_index, foreign_key, check_constraint) AND changeset validations
5. Use contexts for database access — never call Repo directly from web layer
6. Add indexes on foreign keys and frequently queried fields
7. Use timestamps() in every schema — track when records were created/updated

Schema Definition

Define schemas with proper types and associations.