SwiftData uses SQLite by default, but its DataStore protocol allows building custom persistence backends. This deep-dive walks through implementing a JSON-based custom store: creating a JSONStoreConfiguration conforming to DataStoreConfiguration, implementing a JSONStore conforming to DataStore with fetch and save functions, and handling snapshots (DefaultSnapshot) as the bridge between live model objects and the persistence layer. Key concepts covered include how SwiftData converts live models to lightweight snapshots before passing them to the store, how temporary identifiers are remapped to permanent ones on save, and how the SwiftUI view layer remains completely unchanged regardless of the backing store. Tradeoffs like manual constraint enforcement (no built-in uniqueness checks) are also discussed.
