phoenix-context-creator

Phoenix Context Creator

This skill guides the creation of well-designed Phoenix contexts following bounded context principles and Phoenix best practices.

When to Use

• Creating new business domains
• Organizing related functionality
• Refactoring code into contexts
• Designing API boundaries
• Building feature modules

What is a Context?

A context is a module that groups related functionality and provides a public API for that domain. Contexts enforce boundaries between different parts of your application.

Examples:

• Accounts - User management, authentication
• Catalog - Products, categories, inventory
• Sales - Orders, shopping cart, checkout
• CMS - Blog posts, pages, comments
• Notifications - Emails, SMS, push notifications

Context Design Principles

1. Bounded Context

Each context should have clear responsibilities:

# Good: Focused contexts
Accounts.create_user()
Catalog.list_products()
Sales.place_order()

# Bad: Mixed responsibilities
Users.create_user()
Users.list_products()  # Products don't belong here
Users.send_email()     # Email sending doesn't belong here

2. Public API Only

Contexts expose intentional APIs, hide implementation:

# Good: Clear, intention-revealing API
defmodule MyApp.Accounts do
  def list_users, do: Repo.all(User)
  def get_user!(id), do: Repo.get!(User, id)
  def create_user(attrs), do: %User{} |> User.changeset(attrs) |> Repo.insert()
end

# Bad: Exposing internal details
defmodule MyApp.Accounts do
  # Don't expose User schema directly
  def user_schema, do: User

  # Don't expose changesets
  def user_changeset(attrs), do: User.changeset(%User{}, attrs)
end

3. No Cross-Context Dependencies

Contexts should not directly reference other contexts' schemas:

# Bad: Post directly references User schema
defmodule Blog.Post do
  schema "posts" do
    belongs_to :user, Accounts.User  # Direct schema reference
  end
end

# Good: Use IDs to reference across contexts
defmodule Blog.Post do
  schema "posts" do
    field :user_id, :id  # Just store the ID
  end
end

# Then in Blog context, delegate user lookups to Accounts
defmodule Blog do
  def get_post_with_author!(id) do
    post = get_post!(id)
    author = Accounts.get_user!(post.user_id)
    %{post | author: author}
  end
end