liveview-patterns

# LiveView Patterns Reference Reference for building with Phoenix LiveView 1.0/1.1. ## Iron Laws — Never Violate These 1. **NO UNCONDITIONAL DB QUERIES IN MOUNT** — Mount runs TWICE. Default: `assign_async`. SEO routes: `connected?` guard + cache-backed disconnected branch (crawlers read that HTML) 2. **ALWAYS USE STREAMS FOR LISTS** — Regular assigns = O(n) memory per user. Streams = O(1) 3. **CHECK connected?/1 BEFORE SUBSCRIPTIONS** — Prevents double subscriptions 4. **EXTRACT VARIABLES BEFORE assign_async CLOSURE** — Closures copy entire referenced variables 5. **LOAD PRIMARY DATA IN mount/3, PAGINATION IN handle_params/3** — handle_params runs on EVERY URL change 6. **NEVER PASS SOCKET TO BUSINESS LOGIC** — Extract data before calling contexts 7. **CHECK CHANGESET ERRORS BEFORE UI DEBUGGING** — Silent form save = check `{:error, changeset}` first, not viewport/JS 8. **HIDDEN INPUTS FOR ALL REQUIRED EMBEDDED FIELDS** — Every required field in an embedded schema MUST have a `hidden_input` if not directly editable 9. **NEVER USE `assign_new` FOR LIFECYCLE VALUES** — `assign_new` skips the function if key exists. Use `assign/3` for locale, current user, or any value refreshed every mount ## Memory Impact | Pattern | 3K items | 10K users × 10K items | |---------|----------|----------------------| | Regular assigns | ~5.1 MB | ~10+ GB | | Streams | ~1.1 MB | Minimal (O(1)) | **Decision**: Lists with >100 items → Use streams, not assigns ## Quick Patterns ### Async Assi...