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

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.