Rails 37 Style Features Watching

From PR #310:

Before: Separate Subscription Model

# Separate polymorphic subscription table
class Subscription < ApplicationRecord
  belongs_to :user
  delegated_type :subscribable, types: Subscribable::TYPES
end

# Subscribable concern
module Subscribable
  included do
    has_many :subscriptions, as: :subscribable, dependent: :destroy
    has_many :subscribers, through: :subscriptions, source: :user
  end

  def subscribe(user)
    subscriptions.create_or_find_by!(user: user)
  end

  def subscribed_by?(user)
    subscriptions.exists?(user: user)
  end
end

# Bucket model
class Bucket < ApplicationRecord
  include Subscribable
  has_many :accesses
  has_many :users, through: :accesses
end

After: Involvement Enum on Access

# Access model with involvement levels
class Access < ApplicationRecord
  belongs_to :bucket
  belongs_to :user

  enum :involvement, %i[ access_only watching everything ].index_by(&:itself)
end

# Bucket accessible concern
module Bucket::Accessible
  included do
    has_many :accesses, dependent: :destroy
    has_many :users, through: :accesses
    has_many :access_only_users, -> { merge(Access.access_only) },
             through: :accesses, source: :user
  end

  def access_for(user)
    accesses.find_by(user: user)
  end
end

Migration Pattern

class AddInvolvementToAccesses < ActiveRecord::Migration[8.1]
  def change
    change_table :accesses do |t|
      t.string :involvement, null: false, default: "watching"
    end
  end
end

class DropSubscriptions < ActiveRecord::Migration[8.1]
  def change
    # Migrate existing subscription data
    execute <<~SQL
      UPDATE accesses SET involvement = 'access_only'
    SQL

    execute <<~SQL
      UPDATE accesses SET involvement = 'watching'
      FROM (SELECT user_id, subscribable_id as bucket_id FROM subscriptions) AS subscriptions
      WHERE subscriptions.user_id = accesses.user_id
        AND subscriptions.bucket_id = accesses.bucket_id
    SQL

    drop_table :subscriptions
  end
end

Key Takeaway: If you already have a many-to-many relationship (like accesses), consider adding notification preferences there rather than creating a separate subscription system.

2. Simplifying Involvement Levels

Pattern: Start with fewer, clearer notification levels. Resist the temptation to offer too much granularity.

Why it matters: Users rarely understand complex notification settings. Simpler options lead to better UX and easier testing.

From PR #1088:

Before: Three Levels (Confusing)

enum :involvement, %i[ access_only watching everything ].index_by(&:itself)

# Helper labels
def involvement_access_label(collection, involvement)
  case involvement
  when "access_only"
    "Notifications are off for #{collection.name}"
  when "everything"
    "Notifying me about everything in #{collection.name}"
  when "watching"
    "Notifying me only about @mentions and new items in #{collection.name}"
  end
end

After: Two Levels (Clear)

enum :involvement, %i[ access_only watching ].index_by(&:itself)

# Simpler, action-oriented labels
def involvement_access_label(collection, involvement)
  case involvement
  when "access_only"
    "Watch this"
  when "watching"
    "Stop Watching"
  end
end

Notification Logic Simplification

# Before: Different logic for "everything" vs "watching"
def watchers_and_subscribers(include_only_watching: false)
  involvements = include_only_watching ? [:watching, :everything] : :everything
  subscribers = collection.users.where(accesses: { involvement: involvements })
  # ...
end

# After: Single "watching" level
def watchers_and_subscribers(include_only_watching: false)
  involvements = include_only_watching ? [:watching] : []
  subscribers = collection.users.where(accesses: { involvement: involvements })
  # ...
end

Migration to Simplify

class MigrateEverythingAccessesToWatching < ActiveRecord::Migration[8.1]
  def up
    execute <<-SQL
      UPDATE accesses
      SET involvement = 'watching'
      WHERE involvement = 'everything'
    SQL
  end

  def down
    raise ActiveRecord::IrreversibleMigration
  end
end

Key Principles:

• Binary is best: "Watching" vs "Not Watching" is clearer than three+ levels
• Action-oriented labels: "Watch this" is clearer than "Notifications are off"
• Always notify for @mentions and assignments: Don't make users opt into these

3. Separating Resource-Level and Collection-Level Watching

Pattern: Distinguish between watching individual items (cards) vs watching for new items in a collection (boards).

Why it matters: These are different mental models. Users want to watch specific discussions (resource-level) separately from being notified about all new items (collection-level).

From PR #1228 & #1231:

Collection-Level Watching (Boards/Collections)

# Collection accessible concern
module Collection::Accessible
  def watchers
    users.where(accesses: { involvement: :watching })
  end
end

Resource-Level Watching (Cards/Items)

# Card watchable concern
module Card::Watchable
  included do
    has_many :watches, dependent: :destroy
    has_many :watchers, -> { active.merge(Watch.watching) },
             through: :watches, source: :user

    after_create -> { watch_by creator }
  end

  def watched_by?(user)
    watchers.include?(user)
  end

  def watch_by(user)
    watches.where(user: user).first_or_create.update!(watching: true)
  end

  def unwatch_by(user)
    watches.where(user: user).first_or_create.update!(watching: false)
  end
end

Different Notification Logic

# Card events notifier
class Notifier::CardEventNotifier < Notifier
  private
    def recipients
      case source.action
      when "card_assigned"
        # Always notify assignees, regardless of watching status
        source.assignees.excluding(creator)
      when "card_published"
        # Only notify collection watchers for new cards
        collection.watchers.without(creator, *card.mentionees)
      when "comment_created"
        # Only notify card watchers for comments
        card.watchers.without(creator, *source.eventable.mentionees)
      else
        collection.watchers.without(creator)
      end
    end
end

Key Insight: Collection watching is about "notify me of NEW items," while resource watching is about "notify me of UPDATES to this specific item."

4. Toggle UI Patterns with Turbo

Pattern: Use Turbo Streams to update multiple parts of the page when toggling watch status, without full page reloads.

Why it matters: Provides instant feedback and keeps the UI in sync across multiple representations of the same state.

From PR #1239:

Controller Pattern

class Cards::WatchesController < ApplicationController
  include CardScoped

  def create
    @card.watch_by Current.user
    # No redirect - let turbo_stream template handle it
  end

  def destroy
    @card.unwatch_by Current.user
    # No redirect - let turbo_stream template handle it
  end
end

Turbo Stream Template

<!-- app/views/cards/watches/create.turbo_stream.erb -->
<%= render "cards/watches/refresh", card: @card %>

<!-- app/views/cards/watches/_refresh.turbo_stream.erb -->
<%= turbo_stream.replace dom_id(card, :watch_button) do %>
  <%= render "cards/watches/watch_button", card: card %>
<% end %>

<%= turbo_stream.replace dom_id(card, :comment_watchers) do %>
  <%= render "cards/comments/watchers", card: card %>
<% end %>

Partials for Reusability

<!-- app/views/cards/watches/_watch_button.html.erb -->
<div id="<%= dom_id(card, :watch_button) %>">
  <% if card.watched_by? Current.user %>
    <%= button_to card_watch_path(card), method: :delete,
                  class: "btn btn--reversed",
                  data: { controller: "tooltip" } do %>
      <%= icon_tag "bell" %>
      <span class="for-screen-reader">Stop watching</span>
    <% end %>
  <% else %>
    <%= button_to card_watch_path(card),
                  class: "btn",
                  data: { controller: "tooltip" } do %>
      <%= icon_tag "bell-off" %>
      <span class="for-screen-reader">Watch this</span>
    <% end %>
  <% end %>
</div>

<!-- app/views/cards/comments/_watchers.html.erb -->
<div id="<%= dom_id(card, :comment_watchers) %>"
     class="comments__subscribers flex flex-column margin-block-start">
  <strong class="txt-uppercase">Subscribers</strong>

  <p class="margin-none-block-start margin-block-end-half">
    <%= pluralize(card.watchers.without(User.system).count, "person") %>
    will be notified when someone comments on this.
  </p>

  <div class="flex align-center flex-wrap gap-half">
    <% card.watchers.without(User.system).alphabetically.each do |watcher| %>
      <%= avatar_tag watcher %>
    <% end %>
  </div>
</div>

Initial Page Load

<!-- app/views/cards/container/footer/_published.html.erb -->
<aside class="card-perma__actions" role="toolbar">
  <%= turbo_frame_tag card, :watch,
                      src: card_watch_path(card),
                      target: "_top",
                      refresh: :morph %>
</aside>

Key Patterns:

1. Extract partials for the changing UI elements
2. Use dom_id helpers for consistent, unique IDs
3. Update multiple locations in one turbo stream response
4. Lazy load initial state with turbo_frame_tag + src

5. Data Cleanup on Access Removal

Pattern: When a user loses access to a collection/board, automatically clean up their associated watches to prevent orphaned records and privacy issues.

Why it matters: Prevents data leaks where users retain watch subscriptions to resources they can no longer access.

From PR #1519:

Model Pattern

module Board::Accessible
  included do
    # after access is destroyed, clean up related data
    after_destroy_commit :clean_inaccessible_data_for_user,
                         if: -> { user.present? }
  end

  def clean_inaccessible_data_for(user)
    mentions_for_user(user).destroy_all
    notifications_for_user(user).destroy_all
    watches_for(user).destroy_all
  end

  private
    def watches_for(user)
      Watch.where(card: cards, user: user)
    end
end

Add Index for Performance

class AddUserAndCardIndexToWatches < ActiveRecord::Migration[8.2]
  def change
    add_index :watches, %i[ user_id card_id ]
  end
end

Testing Pattern

test "watches are destroyed when access is lost" do
  kevin = users(:kevin)
  board = boards(:writebook)
  card = board.cards.first

  assert card.watched_by?(kevin)

  kevin_access = accesses(:writebook_kevin)

  perform_enqueued_jobs only: Board::CleanInaccessibleDataJob do
    kevin_access.destroy
  end

  assert_not card.watched_by?(kevin)
end

Key Principle: When access is revoked, clean up ALL user-specific state (watches, notifications, mentions, etc.) as part of the same transaction or background job.

6. Cache Invalidation Strategies

Pattern: Use touch: true on associations to automatically invalidate caches when involvement changes.

Why it matters: Keeps cached views up-to-date without manual cache busting logic.

From PR #1088 & #1228:

Touch on Association Changes

class Access < ApplicationRecord
  belongs_to :collection
  belongs_to :user, touch: true  # Invalidates user cache key

  enum :involvement, %i[ access_only watching ].index_by(&:itself)
end

Cache Keys Include User State

class CardsController < ApplicationController
  def index
    @considering = page_and_filter_for @filter.with(engagement_status: "considering")
    @on_deck = page_and_filter_for @filter.with(engagement_status: "on_deck")
    @doing = page_and_filter_for @filter.with(engagement_status: "doing")
    @closed = page_and_filter_for_closed_cards

    # Include user_filtering in cache key (which depends on user.updated_at)
    @cache_key = [@considering, @on_deck, @doing, @closed]
                   .collect { it.page.records }
                   .including([Workflow.all, @user_filtering])

    fresh_when etag: @cache_key
  end
end

Explicit Cache Invalidation for Lists

<!-- Turbo frame to refresh watchers list -->
<%= turbo_frame_tag dom_id(collection, :involvement_button) do %>
  <%= collection_watchers_list(collection) %>
  <%= involvement_button(collection, access, show_watchers) %>
<% end %>

Key Patterns:

1. Touch associations to auto-invalidate when involvement changes
2. Include user state in cache keys for personalized views
3. Use Turbo frames to selectively refresh changed portions

7. Testing Subscription Logic

Pattern: Test the notification logic at multiple levels—model, notifier, and integration.

Why it matters: Notification logic is business-critical and easy to break. Comprehensive tests prevent regressions.

From PRs #310, #1088, #1231:

Model-Level Tests

class Card::WatchableTest < ActiveSupport::TestCase
  setup do
    Watch.destroy_all
    Access.all.update!(involvement: :access_only)
  end

  test "watched_by? when watching" do
    cards(:logo).watch_by users(:kevin)
    assert cards(:logo).watched_by?(users(:kevin))

    cards(:logo).unwatch_by users(:kevin)
    assert_not cards(:logo).watched_by?(users(:kevin))
  end

  test "cards are initially watched by their creator" do
    card = collections(:writebook).cards.create!(creator: users(:kevin))
    assert card.watched_by?(users(:kevin))
  end

  test "watchers" do
    collections(:writebook).access_for(users(:kevin)).watching!
    collections(:writebook).access_for(users(:jz)).watching!

    cards(:logo).watch_by users(:kevin)
    cards(:logo).unwatch_by users(:jz)
    cards(:logo).watch_by users(:david)

    assert_equal [users(:kevin), users(:david)].sort, cards(:logo).watchers.sort

    # Only active users
    users(:david).system!
    assert_equal [users(:kevin)].sort, cards(:logo).watchers.reload.sort
  end
end

Notifier-Level Tests

class Notifier::EventNotifierTest < ActiveSupport::TestCase
  test "published event creates notifications for collection watchers" do
    notifications = Notifier.for(events(:logo_published)).notify
    assert_equal [users(:kevin), users(:jz)], notifications.map(&:user)
  end

  test "assignment events only create a notification for the assignee" do
    collections(:writebook).access_for(users(:jz)).watching!
    collections(:writebook).access_for(users(:kevin)).watching!

    notifications = Notifier.for(events(:logo_assignment_jz)).notify
    assert_equal [users(:jz)], notifications.map(&:user)
  end

  test "assignment events do not notify you if you assigned yourself" do
    collections(:writebook).access_for(users(:david)).watching!

    notifications = Notifier.for(events(:logo_assignment_david)).notify
    assert_empty notifications
  end

  test "assignment events notify assignees regardless of involvement level" do
    # Even access_only users get notified when assigned
    collections(:writebook).access_for(users(:jz)).access_only!

    notifications = Notifier.for(events(:logo_assignment_jz)).notify
    assert_equal [users(:jz)], notifications.map(&:user)
  end

  test "does not create a notification for access-only users" do
    collections(:writebook).access_for(users(:kevin)).access_only!

    notifications = Notifier.for(events(:layout_commented)).notify
    assert_equal [users(:kevin)], notifications.map(&:user)
  end
end

Controller-Level Tests

class Collections::InvolvementsControllerTest < ActionDispatch::IntegrationTest
  setup do
    sign_in_as :kevin
  end

  test "update involvement" do
    collection = collections(:writebook)
    collection.access_for(users(:kevin)).access_only!

    assert_changes -> { collection.access_for(users(:kevin)).involvement },
                   from: "access_only", to: "watching" do
      put collection_involvement_url(collection, involvement: "watching")
    end

    assert_response :success
  end
end

Integration Tests

class Cards::WatchesControllerTest < ActionDispatch::IntegrationTest
  test "create watch" do
    sign_in_as :kevin
    cards(:logo).unwatch_by users(:kevin)

    assert_changes -> { cards(:logo).watched_by?(users(:kevin)) },
                   from: false, to: true do
      post card_watch_path(cards(:logo))
    end
  end

  test "destroy watch" do
    sign_in_as :kevin
    cards(:logo).watch_by users(:kevin)

    assert_changes -> { cards(:logo).watched_by?(users(:kevin)) },
                   from: true, to: false do
      delete card_watch_path(cards(:logo))
    end
  end
end

Test Coverage Checklist:

• Auto-watching on resource creation
• Explicit watch/unwatch actions
• Collection-level involvement changes
• Notification routing based on involvement
• Edge cases (self-assignment, access_only users, etc.)
• Data cleanup when access is removed
• Cache invalidation on involvement changes

Summary of Key Lessons

1. Embed preferences in existing relationships rather than creating separate subscription tables
2. Keep involvement levels simple (binary is best)
3. Separate collection-level and resource-level watching for clarity
4. Use Turbo Streams for high-fidelity toggle UIs that update multiple locations
5. Clean up watches when access is removed to prevent data leaks
6. Touch associations to automatically invalidate caches
7. Test notification logic thoroughly at all levels

These patterns emerged from real-world iteration and refinement in a production application, making them battle-tested and reliable for other Rails apps.