---
name: lv-assigns
description: Inspect LiveView socket assigns for memory bloat — missing temporary_assigns,
unused assigns, unbounded lists needing streams, memory estimates. Use when LiveView
memory grows or you need to add temporary_assigns.
---
# 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
5. **NEVER modify assigns or code during audit** — this is a read-only diagnostic; report findings only
## Quick Audit Commands
### Extract All Assigns
Use Grep to find all `assign(` and `assign_new(` calls in the target LiveView file.
### Find Large Data Patterns
Use Grep to find large data patterns: lists stored in assigns (`assign.*\[\]`, `assign.*Repo\.all`) and full schema storage (`assign.*Repo\.get`) in the target file.
## 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:
Use Grep to extract all assign names (`assign\(:(\w+)`) from the LiveView file, then use Grep to find all `@\w+` references in the corresponding `.heex` template. Compare to find unused assigns.
### 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.