LiveView Assigns Audit
Analyze LiveView socket assigns for memory efficiency, clarity, and best practices.
Iron Laws - Never Violate These
- •Use streams for lists > 100 items - Never store large lists directly in assigns
- •Use temporary_assigns for transient data - Flash messages, temp errors, notifications
- •Preload only needed fields - Don't store full Ecto schemas when only needing subset
- •Initialize all assigns in mount - Never access assigns that might not exist
Quick Audit Commands
Extract All Assigns
bash
grep -E "assign\(|assign_new\(" path/to/live_view.ex
Find Large Data Patterns
bash
# Lists stored in assigns
grep -E "assign.*\[\]|assign.*Repo\.all" path/to/live_view.ex
# Full schema storage
grep -E "assign.*Repo\.get|assign.*%.*\{\}" path/to/live_view.ex
Audit Checklist
1. Memory Issues
| Pattern | Problem | Solution |
|---|---|---|
assign(:items, Repo.all(...)) | Unbounded list | Use stream/3 |
assign(:user, Repo.get!(...)) | Full schema | Select only needed fields |
assign(:file_data, binary) | Large binary | Store reference, not data |
| Nested preloads | Excessive data | Preload only what's rendered |
2. Missing temporary_assigns
Should use temporary_assigns:
- •Flash messages
- •Form errors after submission
- •One-time notifications
- •Upload progress
elixir
def mount(_params, _session, socket) do
{:ok, socket, temporary_assigns: [flash_message: nil]}
end
3. Unused Assigns
Search for assigns defined but never used in templates:
bash
# Find assigns grep -oE "assign\(:(\w+)" live_view.ex | sort -u # Compare with template usage grep -oE "@\w+" template.html.heex | sort -u
4. Missing Initialization
elixir
# BAD: @items might not exist
def render(assigns) do
~H"<%= for item <- @items do %>"
end
# GOOD: Initialize in mount
def mount(_params, _session, socket) do
{:ok, assign(socket, items: [])}
end
Memory Estimation
For each assign, estimate memory footprint:
| Data Type | Approx Size | Concern Level |
|---|---|---|
| Integer | 8 bytes | Low |
| String (100 chars) | ~200 bytes | Low |
| List of 100 maps | ~10-50 KB | Medium |
| List of 1000 items | ~100-500 KB | High |
| Binary (image) | Varies | Critical |
| Full Ecto schema | ~1-5 KB each | Medium |
Usage
Run /lv:assigns path/to/live_view.ex to generate an assigns inventory with memory estimates and optimization recommendations.