ar_relation_scope.rb

require "active_record"
require "rspec/autorun"

class Migrate < ActiveRecord::Migration
  self.verbose = false

  def up
    create_table(:projects)
    create_table(:tasks) do |t|
      t.references :project, null: false
      t.text :external_id
    end
  end
end

class Project < ActiveRecord::Base
  has_many :tasks
end

class Task < ActiveRecord::Base
  ExternalIDAlreadyInUse = Class.new(Exception)

  belongs_to :project

  def self.import_implicit_self(external_id)
    if exists?(external_id: external_id)
      raise ExternalIDAlreadyInUse
    else
      create(external_id: external_id)
    end
  end

  def self.import_explicit_class(external_id)
    if Task.exists?(external_id: external_id)
      raise ExternalIDAlreadyInUse
    else
      create(external_id: external_id)
    end
  end

  def self.import_unscoped(external_id)
    if unscoped.exists?(external_id: external_id)
      raise ExternalIDAlreadyInUse
    else
      create(external_id: external_id)
    end
  end
end

describe "ActiveRecord relation scope" do
  before do
    ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
    Migrate.new.up
  end

  it "has an implicit scope when used with implicit self" do
    one = Project.create
    two = Project.create

    one.tasks.import_implicit_self(1)
    two.tasks.import_implicit_self(1)
  end

  it "has an implicit scope when used with explicit class" do
    one = Project.create
    two = Project.create

    one.tasks.import_explicit_class(1)
    two.tasks.import_explicit_class(1)
  end

  it "can be unscoped" do
    one = Project.create
    two = Project.create

    one.tasks.import_unscoped(1)

    expect {
      two.tasks.import_unscoped(1)
    }.to raise_error(Task::ExternalIDAlreadyInUse)
  end
end