LiveView Assigns Audit

Analyze LiveView socket assigns for memory efficiency, clarity, and best practices.

Iron Laws - Never Violate These

1. Use streams for lists > 100 items - Never store large lists directly in assigns
2. Use temporary_assigns for transient data - Flash messages, temp errors, notifications
3. Preload only needed fields - Don't store full Ecto schemas when only needing subset
4. Initialize all assigns in mount - Never access assigns that might not exist

Quick Audit Commands

Extract All Assigns

grep -E "assign\(|assign_new\(" path/to/live_view.ex

Find Large Data Patterns

# 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

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:

# 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

# 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.