discourse/app/models/group_user.rb

require_dependency 'notification_levels'

class GroupUser < ActiveRecord::Base
  belongs_to :group, counter_cache: "user_count"
  belongs_to :user

  after_save :update_title
  after_destroy :grant_other_available_title

  after_save :set_primary_group
  after_destroy :remove_primary_group, :recalculate_trust_level

  before_create :set_notification_level
  after_save :grant_trust_level

  def self.notification_levels
    NotificationLevels.all
  end

  protected

  def set_notification_level
    self.notification_level = group&.default_notification_level || 3
  end

  def set_primary_group
    if group.primary_group
      DB.exec("
        UPDATE users
        SET primary_group_id = :id
        WHERE id = :user_id",
        id: group.id, user_id: user_id
      )
    end
  end

  def remove_primary_group
    DB.exec("
      UPDATE users
      SET primary_group_id = NULL
      WHERE id = :user_id AND primary_group_id = :id",
      id: group.id, user_id: user_id
    )
  end

  def grant_other_available_title
    if group.title.present? && group.title == user.title
      user.update!(title: user.next_best_title)
    end
  end

  def update_title
    if group.title.present?
      DB.exec("
        UPDATE users SET title = :title
        WHERE (title IS NULL OR title = '') AND id = :id",
        id: user_id, title: group.title
      )
    end
  end

  def grant_trust_level
    return if group.grant_trust_level.nil?

    if (user.group_locked_trust_level || 0) < group.grant_trust_level
      user.update!(group_locked_trust_level: group.grant_trust_level)
    end

    TrustLevelGranter.grant(group.grant_trust_level, user)
  end

  def recalculate_trust_level
    return if group.grant_trust_level.nil?

    # Find the highest level of the user's remaining groups
    highest_level = GroupUser
      .where(user_id: user.id)
      .includes(:group)
      .maximum("groups.grant_trust_level")

    user.update!(group_locked_trust_level: highest_level)
    Promotion.recalculate(user)
  end
end

# == Schema Information
#
# Table name: group_users
#
#  id                 :integer          not null, primary key
#  group_id           :integer          not null
#  user_id            :integer          not null
#  created_at         :datetime         not null
#  updated_at         :datetime         not null
#  owner              :boolean          default(FALSE), not null
#  notification_level :integer          default(2), not null
#
# Indexes
#
#  index_group_users_on_group_id_and_user_id  (group_id,user_id) UNIQUE
#  index_group_users_on_user_id_and_group_id  (user_id,group_id) UNIQUE
#