LiveView Patterns Reference

Reference for building with Phoenix LiveView 1.0/1.1.

Iron Laws — Never Violate These

1. NO DATABASE QUERIES IN DISCONNECTED MOUNT — Queries run TWICE (HTTP + WebSocket). Use assign_async
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