Agent skill

phoenix-generator

Generate Phoenix resources (contexts, schemas, LiveViews, controllers) using mix phx.gen.* commands with best practices. Use when creating new Phoenix resources, contexts, or LiveView components.

View SKILL.md on GitHub Repository
Stars 163
Forks 31

Install this agent skill to your Project

npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/phoenix-generator

SKILL.md

Phoenix Generator

This skill helps generate Phoenix resources using built-in generators with proper patterns and best practices.

When to Use

  • Creating new Phoenix contexts
  • Adding schemas to existing contexts
  • Generating LiveView CRUD interfaces
  • Creating JSON/HTML resources
  • Scaffolding authentication

Available Generators

Context and Schema Generation

mix phx.gen.context - Generate a context with schema and migration

bash
mix phx.gen.context Accounts User users name:string email:string:unique age:integer

Generates:

  • Context module: lib/my_app/accounts.ex
  • Schema: lib/my_app/accounts/user.ex
  • Migration: priv/repo/migrations/*_create_users.exs
  • Test files

mix phx.gen.schema - Schema and migration only (no context)

bash
mix phx.gen.schema Accounts.User users name:string email:string:unique

LiveView Generators

mix phx.gen.live - Full LiveView CRUD with context

bash
mix phx.gen.live Catalog Product products \
  name:string \
  description:text \
  price:decimal \
  sku:string:unique \
  in_stock:boolean

Generates:

  • Context and schema
  • LiveView modules (Index, Show, Form Component)
  • Routes
  • Tests

mix phx.gen.live.component - Standalone LiveView component

bash
mix phx.gen.live.component Components.Modal

Traditional Web Generators

mix phx.gen.html - HTML resource with controllers

bash
mix phx.gen.html Blog Post posts title:string body:text published:boolean

mix phx.gen.json - JSON API resource

bash
mix phx.gen.json Shop Product products name:string price:decimal

Field Types and Modifiers

Common Field Types

  • string - varchar(255)
  • text - unlimited text
  • integer - whole numbers
  • decimal - precise decimals (for money)
  • float - floating point
  • boolean - true/false
  • date - date only
  • time - time only
  • datetime - timestamp
  • uuid - UUID
  • binary - binary data

Field Modifiers

  • :unique - adds unique index
  • :redact - marks for redaction in logs
  • name:string:unique:redact - chain modifiers

References (Associations)

bash
# belongs_to
mix phx.gen.context Blog Post posts \
  title:string \
  body:text \
  user_id:references:users

# Specify custom reference
mix phx.gen.context Comments Comment comments \
  body:text \
  post_id:references:posts \
  author_id:references:users

Best Practices

1. Context Naming

  • Use plural for context: Accounts, Catalog, Blog
  • Use singular for schema: User, Product, Post
  • Table name matches schema plural: users, products, posts

2. Field Selection

bash
# Good: Specific types
price:decimal         # For money
published_at:datetime # For timestamps
active:boolean        # For flags

# Avoid: Wrong types
price:float          # Loses precision for money
published:string     # Use datetime or boolean

3. Associations

bash
# Always specify references explicitly
user_id:references:users

# Don't use bare integer for foreign keys
user_id:integer  # Missing association metadata

4. Decimal Precision

For money fields, update migration:

elixir
# Generated
add :price, :decimal

# Best Practice - specify precision
add :price, :decimal, precision: 10, scale: 2

5. String Length Limits

Update schema for validation:

elixir
# Add to changeset
|> validate_length(:name, max: 100)
|> validate_length(:email, max: 160)

Generator Workflow

Step 1: Plan Schema

bash
# List fields with types
name:string
email:string:unique
age:integer
bio:text
admin:boolean
inserted_at:datetime
updated_at:datetime  # automatic with timestamps()

Step 2: Generate Resource

bash
# Choose appropriate generator
mix phx.gen.live Accounts User users \
  name:string \
  email:string:unique \
  age:integer \
  bio:text \
  admin:boolean

Step 3: Review Generated Files

  • Check migration for proper indexes and constraints
  • Review schema for additional validations needed
  • Update context functions as needed
  • Review tests and add edge cases

Step 4: Customize Migration

bash
# Before running migration, edit it
vim priv/repo/migrations/*_create_users.exs

Add:

  • Check constraints
  • Default values
  • Additional indexes
  • Precision for decimals

Step 5: Add Routes (if needed)

elixir
# lib/my_app_web/router.ex
scope "/", MyAppWeb do
  pipe_through :browser

  live "/users", UserLive.Index, :index
  live "/users/new", UserLive.Index, :new
  live "/users/:id/edit", UserLive.Index, :edit
  live "/users/:id", UserLive.Show, :show
  live "/users/:id/show/edit", UserLive.Show, :edit
end

Step 6: Run Migration

bash
mix ecto.migrate

Step 7: Update Tests

  • Add validation tests
  • Add association tests
  • Test edge cases

Common Patterns

Money Fields

bash
mix phx.gen.live Shop Product products \
  name:string \
  price:decimal \
  sale_price:decimal

Then update migration:

elixir
add :price, :decimal, precision: 10, scale: 2, null: false
add :sale_price, :decimal, precision: 10, scale: 2

Soft Deletes

Add to schema:

bash
deleted_at:datetime

Update migration:

elixir
add :deleted_at, :utc_datetime
create index(:products, [:deleted_at])

Polymorphic Associations

bash
mix phx.gen.schema Comments.Comment comments \
  body:text \
  commentable_type:string \
  commentable_id:integer

Multi-tenant (Tenant ID)

bash
mix phx.gen.live Accounts User users \
  organization_id:references:organizations \
  name:string \
  email:string

Add unique constraint on tenant + field:

elixir
create unique_index(:users, [:organization_id, :email])

Undoing Generators

If you need to rollback:

bash
# Rollback migration
mix ecto.rollback

# Delete generated files manually or use:
mix phx.gen.context --undo Accounts User users

Troubleshooting

Module already exists:

  • Generator won't overwrite existing files
  • Use --merge-with-existing-context to add to existing context
  • Or manually integrate generated code

Routes not working:

  • Check router.ex was updated
  • Verify pipe_through matches (:browser or :api)
  • Restart server after adding routes

Migration fails:

  • Check for duplicate table names
  • Verify referenced tables exist
  • Ensure field types are valid

Generator Flags

bash
# Skip migration
mix phx.gen.context Accounts User users name:string --no-migration

# Binary ID (UUID)
mix phx.gen.schema Accounts User users name:string --binary-id

# Merge with existing context
mix phx.gen.context Accounts Profile profiles bio:text --merge-with-existing-context

# Specify table name
mix phx.gen.schema Accounts User my_users name:string --table my_users

Recommended Agent Skills

Expand your agent's capabilities with these related and highly-rated skills.

majiayu000/claude-skill-registry

agent-ops-spec

Manage specification documents in .agent/specs/. Use when user provides requirements, acceptance criteria, or feature descriptions that need to be tracked and validated against implementation.

163 31
Explore
majiayu000/claude-skill-registry

agent-ops-state

Maintain .agent state files. Use at session start, after meaningful steps, and before concluding: read/update constitution/memory/focus/issues/baseline consistently.

163 31
Explore
majiayu000/claude-skill-registry

agent-ops-spec

Manage specification documents in .agent/specs/. Use when user provides requirements, acceptance criteria, or feature descriptions that need to be tracked and validated against implementation.

163 31
Explore
majiayu000/claude-skill-registry

agent-ops-testing

Test strategy, execution, and coverage analysis. Use when designing tests, running test suites, or analyzing test results beyond baseline checks.

163 31
Explore
majiayu000/claude-skill-registry

agent-ops-testing

Test strategy, execution, and coverage analysis. Use when designing tests, running test suites, or analyzing test results beyond baseline checks.

163 31
Explore
majiayu000/claude-skill-registry

agent-ops-state

Maintain .agent state files. Use at session start, after meaningful steps, and before concluding: read/update constitution/memory/focus/issues/baseline consistently.

163 31
Explore

Didn't find tool you were looking for?

Be as detailed as possible for better results