F# Persistence Patterns

Philosophy: I/O at the Edges

Persistence is where data meets the outside world. Keep it isolated, explicit about effects, and separate from business logic. The rest of your code should be pure; persistence is where impurity lives.

Before implementing persistence, ask:

• What's the simplest storage that meets the requirements?
• What queries do I need? (Design for access patterns)
• What needs to be transactional?
• How do I handle "not found" vs errors?

Core Principles:

1. Async Everything: All I/O is async. No blocking database calls in an async application.

2. Options for Absence: When something might not exist, return Option<'T>. Don't return null, don't throw exceptions.

3. Parameterized Always: Every query uses parameters. SQL injection is never acceptable.