lv: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

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

# 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.