Data Modeling And Sync

Data Modeling & Sync

Ensure data integrity across iPhone and Apple Watch, with predictable conflict handling and resilient offline behavior.

When to use this skill

• When adding new data models or persistence changes
• After any WCSession messaging changes
• Before App Store submission
• When users report missing or out-of-sync data

Step 1: Model Stability & Migrations

Checklist:

• Models have stable identifiers (UUID or stable hash)
• Stored models include schema version
• Migration strategy exists for added/removed fields

If using Codable + UserDefaults:

• Provide default values for new fields
• Handle missing keys gracefully

Step 2: WCSession Reliability

WATCH_DIR="YourApp Watch App"

# WCSession usage
rg --type swift 'WCSession|sendMessage|transferUserInfo|updateApplicationContext' "$WATCH_DIR/"
rg --type swift 'WCSession' YourApp/

Checklist:

• WCSession.isReachable only used for interactive UI messages
• transferUserInfo for eventual delivery
• updateApplicationContext for latest state only
• Retries or fallbacks for failures

Step 3: Conflict Resolution

Define a clear strategy:

• Last-write-wins with timestamps, or
• Merge by stable ID, or
• User choice for conflicts

Ensure conflict handling is deterministic and tested.

Step 4: Offline & Edge Cases

Checklist:

• App behaves predictably offline
• Pending changes queued and replayed
• No data loss if watch/app restarts mid-sync

Step 5: Data Integrity Tests

Suggested tests:

• Encode/decode round-trip for each model
• Migration tests between schema versions
• Sync payload validation
• Conflict-resolution unit tests

Output Format