Database Transaction Management

Implement transaction management for:

Database: [PostgreSQL/MySQL/SQL Server]
Framework/ORM: [Prisma/TypeORM/SQLAlchemy/etc.]
Language: [Node.js/Python/Java/etc.]

Use Case:
[DESCRIBE THE OPERATIONS THAT NEED TRANSACTION HANDLING]

Requirements:
- Concurrent access patterns: [DESCRIBE]
- Consistency requirements: [STRONG/EVENTUAL]
- Deadlock risk: [HIGH/LOW]

Please provide:
1. Appropriate isolation level selection with justification
2. Transaction implementation code
3. Error handling and rollback procedures
4. Deadlock prevention strategies
5. Nested transaction handling (savepoints)
6. Testing strategies for transaction behavior