Add interactor MergeContactLists

app/interactors/merge_contact_lists.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class MergeContactLists
+  include Interactor
+
+  after do
+    context.from.contacts.reload
+    context.to.contacts.reload
+  end
+
+  def call
+    ActiveRecord::Base.transaction do
+      context.from.contacts.each do |contact|
+        contact.update! contact_list: context.to
+      end
+    end
+  end
+end

app/models/contact_list.rb

@@ -8,4 +8,6 @@ class ContactList < ApplicationRecord
   has_one :account
 
   has_one :person
+
+  has_many :contacts, dependent: :restrict_with_exception
 end

factories/contact_lists.rb

@@ -2,4 +2,16 @@
 
 FactoryBot.define do
   factory :empty_contact_list, class: ContactList
+
+  factory :some_contact_list, parent: :empty_contact_list do
+    transient do
+      contacts_count { rand 1..5 }
+    end
+
+    after :create do |contact_list, evaluator|
+      create_list :some_contact,
+                  evaluator.contacts_count,
+                  contact_list: contact_list
+    end
+  end
 end

spec/interactors/merge_contact_lists_spec.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe MergeContactLists do
+  subject { described_class.call from: from, to: to }
+
+  let(:from) { create :some_contact_list }
+  let(:to)   { create :some_contact_list }
+
+  specify do
+    expect { subject }.to \
+      change(from.contacts, :count)
+      .from(from.contacts.count)
+      .to(0)
+  end
+
+  specify do
+    expect { subject }.to \
+      change(to.contacts, :count)
+      .from(to.contacts.count)
+      .to(from.contacts.count + to.contacts.count)
+  end
+
+  specify do
+    expect { subject }.to \
+      change(from.contacts, :to_a)
+      .from(from.contacts.to_a)
+      .to([])
+  end
+
+  specify do
+    expect { subject }.to \
+      change(to.contacts, :to_a)
+      .from(to.contacts.to_a)
+      .to(to.contacts.to_a + from.contacts.to_a)
+  end
+end

spec/models/contact_list_spec.rb

@@ -20,4 +20,12 @@ RSpec.describe ContactList do
         .dependent(:restrict_with_exception)
     end
   end
+
+  describe '#contacts' do
+    it do
+      is_expected.to \
+        have_many(:contacts)
+        .dependent(:restrict_with_exception)
+    end
+  end
 end