diff --git a/.github/workflows/minitest.yml b/.github/workflows/minitest.yml
index 9d3968f08..a7a28ed34 100644
--- a/.github/workflows/minitest.yml
+++ b/.github/workflows/minitest.yml
@@ -26,6 +26,9 @@ jobs:
       - name: Setup Postgres
         id: setup-postgres
         uses: alphagov/govuk-infrastructure/.github/actions/setup-postgres@main
+        with:
+          POSTGRES_IMAGE_TAG: 16
+          POSTGRES_DB: publisher_test
 
       - name: Setup Redis
         uses: alphagov/govuk-infrastructure/.github/actions/setup-redis@main
@@ -57,10 +60,13 @@ jobs:
       - name: Initialize database
         env:
           RAILS_ENV: test
+          TEST_DATABASE_URL: ${{ steps.setup-postgres.outputs.db-url }}
         run: bundle exec rails db:setup
 
       - name: Run Minitest
         env:
           RAILS_ENV: test
+          TEST_DATABASE_URL: ${{ steps.setup-postgres.outputs.db-url }}
+          TEST_MONGODB_URI: mongodb://localhost:27017/publisher_test
           GOVUK_CONTENT_SCHEMAS_PATH: vendor/publishing-api/content_schemas
         run: bundle exec rake test
diff --git a/Gemfile b/Gemfile
index b2b919c34..243dbe6da 100644
--- a/Gemfile
+++ b/Gemfile
@@ -32,6 +32,7 @@ gem "mongoid-sadstory"
 gem "mousetrap-rails"
 gem "nested_form", git: "https://github.com/alphagov/nested_form.git", branch: "add-wrapper-class"
 gem "null_logger"
+gem "pg"
 gem "plek"
 gem "prometheus-client"
 gem "rails_autolink"
@@ -41,20 +42,17 @@ gem "sentry-sidekiq"
 gem "sidekiq", "< 8" # Disables Sidekiq 7 beta opt-in.
 gem "sprockets-rails"
 gem "state_machines"
+gem "state_machines-activerecord"
 gem "state_machines-mongoid"
 gem "strip_attributes"
 gem "terser"
 gem "whenever", require: false
 
-# postgres dependencies
-gem "pg"
-gem "state_machines-activerecord"
-gem "database_cleaner-active_record"
-
 group :test do
   gem "capybara-select-2"
   gem "ci_reporter_minitest"
   gem "climate_control"
+  gem "database_cleaner-active_record"
   gem "database_cleaner-mongoid"
   gem "factory_bot_rails"
   gem "govuk_schemas"
diff --git a/app/helpers/publications_helper.rb b/app/helpers/publications_helper.rb
index 1fca9d6b3..16ca6862e 100644
--- a/app/helpers/publications_helper.rb
+++ b/app/helpers/publications_helper.rb
@@ -15,7 +15,7 @@ def content_tagger_url(edition)
   end
 
   def enabled_users_select_options
-    options = User.enabled.order_by([%i[name asc]]).collect { |u| [u.name, u.id] }
+    options = User.enabled.order([:name]).collect { |u| [u.name, u.id] }
     options.unshift(["", ""])
   end
 end
diff --git a/app/helpers/tabbed_nav_helper.rb b/app/helpers/tabbed_nav_helper.rb
index 08c8e965b..5713f7990 100644
--- a/app/helpers/tabbed_nav_helper.rb
+++ b/app/helpers/tabbed_nav_helper.rb
@@ -84,7 +84,7 @@ def available_assignee_items(edition)
       items << { value: "none", text: "None" }
       items << :or
     end
-    User.enabled.order_by([%i[name asc]]).each do |user|
+    User.enabled.order([:name]).each do |user|
       items << { value: user.id, text: user.name } unless user.name == edition.assignee || !user.has_editor_permissions?(edition)
     end
     items
diff --git a/app/lib/govuk_content_models/action_processors/assign_processor.rb b/app/lib/govuk_content_models/action_processors/assign_processor.rb
index b74f0ca32..c930c5d07 100644
--- a/app/lib/govuk_content_models/action_processors/assign_processor.rb
+++ b/app/lib/govuk_content_models/action_processors/assign_processor.rb
@@ -2,8 +2,10 @@ module GovukContentModels
   module ActionProcessors
     class AssignProcessor < BaseProcessor
       def process
-        edition.set(assigned_to_id: action_attributes[:recipient_id])
+        # rubocop:disable Rails/SaveBang
+        edition.update(assigned_to_id: action_attributes[:recipient_id])
         edition.reload
+        # rubocop:enable Rails/SaveBang
       end
     end
   end
diff --git a/app/lib/tagging/tagging_update_form.rb b/app/lib/tagging/tagging_update_form.rb
index d55b7aa68..5ba3c363e 100644
--- a/app/lib/tagging/tagging_update_form.rb
+++ b/app/lib/tagging/tagging_update_form.rb
@@ -6,7 +6,7 @@ class TaggingUpdateForm
     validate :ordered_related_items_paths_exist
 
     def self.build_from_publishing_api(content_id, locale)
-      link_set = LinkSet.find(content_id, locale)
+      link_set = Tagging::LinkSet.find(content_id, locale)
 
       new(
         content_id:,
diff --git a/app/models/action.rb b/app/models/action.rb
index d2dd37529..de53aba8e 100644
--- a/app/models/action.rb
+++ b/app/models/action.rb
@@ -30,8 +30,13 @@ class Action
 
   embedded_in :edition
 
-  belongs_to :recipient, class_name: "User", optional: true
-  belongs_to :requester, class_name: "User", optional: true
+  # Temp-to-be-brought-back
+  # Currently we are using recipient_id & requester_id as a field to store the id's
+  # to bypass the issue of having a belongs_to between a postgres table and a mongo table
+  # we will most likely bring back the belongs_to relationship once we move action table to postgres.
+
+  # belongs_to :recipient, class_name: "User", optional: true
+  # belongs_to :requester, class_name: "User", optional: true
 
   field :approver_id,        type: Integer
   field :approved,           type: DateTime
@@ -43,6 +48,12 @@ class Action
   field :customised_message, type: String
   field :created_at,         type: DateTime, default: -> { Time.zone.now }
 
+  # Temp-to-be-removed
+  # This will be removed once we move action table to postgres, this temporarily
+  # allows to support the belongs to relation between action and user
+  field :recipient_id,       type: BSON::ObjectId
+  field :requester_id,       type: BSON::ObjectId
+
   def container_class_name(edition)
     edition.container.class.name.underscore.humanize
   end
@@ -65,4 +76,27 @@ def is_fact_check_request?
     # SEND_FACT_CHECK is now a state - in older publications it isn't
     [SEND_FACT_CHECK, "fact_check_requested"].include?(request_type)
   end
+
+  # Temp-to-be-removed
+  # The method below are getters and setters for assigned_to that allows us to set the requester & requester_id and get recipient & recipient_id.
+  # We are unable to use [belongs_to :recipient, class_name: "User", optional: true & belongs_to :requester, class_name: "User", optional: true] as the User table is
+  # in postgres and using a combination of setter and getter methods with a recipient_id & requester_id field
+  # to be able to achieve congruent result as having a belongs to while we are moving other table to postgres
+  def recipient
+    User.find(recipient_id) if recipient_id
+  end
+
+  def requester
+    User.find(requester_id) if requester_id
+  rescue StandardError
+    nil
+  end
+
+  def recipient=(user)
+    self.recipient_id = user.id
+  end
+
+  def requester=(user)
+    self.requester_id = user.id
+  end
 end
diff --git a/app/models/application_record.rb b/app/models/application_record.rb
new file mode 100644
index 000000000..10a4cba84
--- /dev/null
+++ b/app/models/application_record.rb
@@ -0,0 +1,3 @@
+class ApplicationRecord < ActiveRecord::Base
+  self.abstract_class = true
+end
diff --git a/app/models/artefact.rb b/app/models/artefact.rb
index 8c0465bba..063598c9d 100644
--- a/app/models/artefact.rb
+++ b/app/models/artefact.rb
@@ -216,6 +216,12 @@ def record_action(action_type, options = {})
       attributes[:user] = user if user
       attributes[:task_performed_by] = task_name if task_name
 
+      # Temp-to-be-removed
+      # This will be removed once we move artefact table to postgres, currently record_action
+      # when called with options contains the user object attributes that is supported by belongs to
+      # the below code allows to use the user id foreign key instead as we are temporarily not using belongs to
+      # relationship between artefact and user
+      add_user_id_and_delete_user_key(attributes)
       new_action = actions.build(attributes)
       # Mongoid will not fire creation callbacks on embedded documents, so we
       # need to trigger this manually. There is a `cascade_callbacks` option on
@@ -225,6 +231,13 @@ def record_action(action_type, options = {})
     end
   end
 
+  def add_user_id_and_delete_user_key(attributes)
+    if attributes[:user]
+      attributes[:user_id] = attributes[:user].id
+      attributes.delete(:user)
+    end
+  end
+
   def archived?
     state == "archived"
   end
diff --git a/app/models/artefact_action.rb b/app/models/artefact_action.rb
index df18f8adc..533bce5fd 100644
--- a/app/models/artefact_action.rb
+++ b/app/models/artefact_action.rb
@@ -6,12 +6,27 @@ class ArtefactAction
   field "snapshot", type: Hash
   field "task_performed_by", type: String
 
+  # Temp-to-be-removed
+  # This will be removed once we move artefact_action table to postgres, this temporarily
+  # allows to support the belongs_to relation between artefact_action and user
+  field "user_id", type: BSON::ObjectId
+
   embedded_in :artefact
 
   # Ideally we would like to use the UID field here, since that will be the
   # same across all applications, but Mongoid doesn't yet support using a
   # custom primary key on a related field
-  belongs_to :user, optional: true
+
+  # Temp-to-be-brought-back
+  # Currently we are using user_id as a field to store the user_id
+  # to bypass the issue of having a belongs_to between a postgres table and a mongo table
+  # we will most likely bring back the belongs_to relationship once we move artefact_action table to postgres.
+
+  # belongs_to :user, optional: true
+
+  def user
+    User.find(user_id) if user_id
+  end
 
   # Not validating presence of a user just yet, since there may be some
   # circumstances where we can't reliably determine the user. As an example
diff --git a/app/models/edition.rb b/app/models/edition.rb
index fe571ad09..92e21d487 100644
--- a/app/models/edition.rb
+++ b/app/models/edition.rb
@@ -33,11 +33,21 @@ class ResurrectionError < RuntimeError
   field :change_note,          type: String
   field :review_requested_at,  type: DateTime
 
+  # Temp-to-be-removed
+  # This will be removed once we move edition table to postgres, this temporarily
+  # allows to support the belongs_to relation between edition and user
+  field :assigned_to_id,       type: BSON::ObjectId
+
   field :auth_bypass_id,       type: String, default: -> { SecureRandom.uuid }
 
   field :owning_org_content_ids, type: Array, default: []
 
-  belongs_to :assigned_to, class_name: "User", optional: true
+  # Temp-to-be-brought-back
+  # Currently we are using assigned_to_id as a field to store the assigned_to_id
+  # to bypass the issue of having a belongs_to between a postgres table and a mongo table
+  # we will most likely bring back the belongs_to relationship once we move edition table to postgres.
+
+  # belongs_to :assigned_to, class_name: "User", optional: true
 
   embeds_many :link_check_reports
 
@@ -521,6 +531,24 @@ def is_accessible_to?(user)
     owning_org_content_ids.include?(user.organisation_content_id)
   end
 
+  # Temp-to-be-removed
+  # The method below are getters and setters for assigned_to that allows us to set the assigned_to_id and get assigned_to.
+  # We are unable to use belongs_to :assigned_to, class_name: "User as the User table is
+  # in postgres and using a combination of setter and getter methods with a assigned_to_id field
+  # to be able to achieve congruent result as  having a belongs to while we are moving other table to postgres
+
+  def assigned_to_id=(id)
+    self[:assigned_to_id] = id
+  end
+
+  def assigned_to=(user)
+    self[:assigned_to_id] = user.id
+  end
+
+  def assigned_to
+    User.find(assigned_to_id) if assigned_to_id
+  end
+
 private
 
   def base_field_keys
diff --git a/app/models/user.rb b/app/models/user.rb
index 81a0666f3..2e82b1fac 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -3,40 +3,11 @@
 require "gds-sso/user"
 require_dependency "safe_html"
 
-class User
-  include Mongoid::Document
-  include Mongoid::Timestamps
+class User < ApplicationRecord
   include GDS::SSO::User
 
-  # Let an app configure the symbolized collection name to use,
-  # e.g. set a constant in an initializer.
-  if defined?(USER_COLLECTION_NAME)
-    store_in collection: USER_COLLECTION_NAME.to_sym
-  else
-    store_in collection: :users
-  end
-
-  field "name",                    type: String
-  field "uid",                     type: String
-  field "version",                 type: Integer
-  field "email",                   type: String
-  field "permissions",             type: Array, default: []
-  field "remotely_signed_out",     type: Boolean, default: false
-  field "organisation_slug",       type: String
-  field "disabled",                type: Boolean, default: false
-  field "organisation_content_id", type: String
-
-  index({ uid: 1 }, unique: true)
-  index disabled: 1
-
-  scope :alphabetized, -> { order_by(name: :asc) }
-  scope :enabled,
-        lambda {
-          any_of(
-            { :disabled.exists => false },
-            { :disabled.in => [false, nil] },
-          )
-        }
+  scope :alphabetized, -> { order(name: :asc) }
+  scope :enabled, -> { where("disabled IS NULL OR disabled = ?", false) }
 
   def to_s
     name || email || ""
diff --git a/app/models/workflow.rb b/app/models/workflow.rb
index 7504e007a..6c09be1f7 100644
--- a/app/models/workflow.rb
+++ b/app/models/workflow.rb
@@ -12,7 +12,18 @@ class CannotDeletePublishedPublication < RuntimeError; end
     after_create :notify_siblings_of_new_edition
 
     field :state, type: String, default: "draft"
-    belongs_to :assigned_to, class_name: "User", optional: true
+
+    # Temp-to-be-removed
+    # This will be removed once we move workflow module to support postgres models, this temporarily
+    # allows to support the belongs_to relation between workflow and user
+    field :assigned_to_id, type: BSON::ObjectId
+
+    # Temp-to-be-brought-back
+    # Currently we are using assigned_to_id as a field to store the assigned_to_id
+    # to bypass the issue of having a belongs_to between a postgres table and a mongo table
+    # we will most likely bring back the belongs_to relationship once we move workflow to support postgres.
+
+    # belongs_to :assigned_to, class_name: "User", optional: true
 
     state_machine initial: :draft do
       after_transition on: :request_amendments do |edition, _transition|
@@ -191,6 +202,17 @@ def important_note
     action if action.try(:request_type) == Action::IMPORTANT_NOTE
   end
 
+  # Temp-to-be-removed
+  # The method below are getters and setters for assigned_to that allows us to set the assigned_to_id and get assigned_to.
+  # We are unable to use belongs_to :assigned_to, class_name: "User as the User table is
+  # in postgres and using a combination of setter and getter methods with a assigned_to_id field
+  # to be able to achieve congruent result as  having a belongs to while we are moving other table to postgres
+  delegate :assigned_to_id=, to: self
+
+  def assigned_to
+    User.find(assigned_to_id) if assigned_to_id
+  end
+
 private
 
   def notify_siblings_of_published_edition
diff --git a/app/presenters/filtered_editions_presenter.rb b/app/presenters/filtered_editions_presenter.rb
index e87b025fc..fad72db9c 100644
--- a/app/presenters/filtered_editions_presenter.rb
+++ b/app/presenters/filtered_editions_presenter.rb
@@ -129,9 +129,9 @@ def apply_assigned_to_filter(editions)
       editions = editions.assigned_to(nil)
     else
       begin
-        assigned_user = User.find(assigned_to_filter)
+        assigned_user = User.find(assigned_to_filter) if assigned_to_filter.present?
         editions = editions.assigned_to(assigned_user) if assigned_user
-      rescue Mongoid::Errors::DocumentNotFound
+      rescue ActiveRecord::RecordNotFound
         Rails.logger.warn "An attempt was made to filter by an unknown user ID: '#{assigned_to_filter}'"
       end
     end
diff --git a/app/views/legacy_editions/_reviewer_field.html.erb b/app/views/legacy_editions/_reviewer_field.html.erb
index 390dcae1d..7d82746fe 100644
--- a/app/views/legacy_editions/_reviewer_field.html.erb
+++ b/app/views/legacy_editions/_reviewer_field.html.erb
@@ -1,3 +1,3 @@
 <%= form_group(f, :reviewer, label: "Reviewer") do %>
-  <%= f.select :reviewer, User.enabled.order_by([[:name, :asc]]).collect{ |p| [p.name, p.name] }, { :include_blank => true }, { :class => "form-control input-md-3", :disabled => @resource.locked_for_edits?, "data-module" => "assignee-select"} %>
+  <%= f.select :reviewer, User.enabled.order([:name]).collect{ |p| [p.name, p.name] }, { :include_blank => true }, { :class => "form-control input-md-3", :disabled => @resource.locked_for_edits?, "data-module" => "assignee-select"} %>
 <% end %>
diff --git a/config/application.rb b/config/application.rb
index 64d79e477..9e0dd3d35 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -3,6 +3,7 @@
 require "rails"
 # Pick the frameworks you want:
 require "active_model/railtie"
+require "active_record/railtie"
 require "active_job/railtie"
 require "action_controller/railtie"
 require "action_mailer/railtie"
@@ -67,7 +68,7 @@ class Application < Rails::Application
     }
 
     config.generators do |g|
-      g.orm :mongoid
+      g.orm :active_record
       g.template_engine :erb # this could be :haml or whatever
       g.test_framework :test_unit, fixture: false # this could be :rpsec or whatever
     end
diff --git a/config/database.yml b/config/database.yml
index aa9fc33ca..dc534671a 100644
--- a/config/database.yml
+++ b/config/database.yml
@@ -7,34 +7,23 @@ default: &default
 
 development:
   <<: *default
-  database: publisher_development
-  username: publisher
-  password: publisher
   clients:
     default:
-      uri: <%= "postgresql://postgres@postgres-13/publisher" %>
+      uri: <%= ENV['DATABASE_URL'] || "postgresql://postgres@postgres-16/publisher" %>
   options:
-#    use_activesupport_time_zone: true
-#    belongs_to_required_by_default: false
 
-test:
+test: &test
   <<: *default
-  clients:
-    default:
-      uri: <%= "postgresql://postgres@postgres-13/publisher" %>
-      options:
-        read:
-          mode: :primary
-        max_pool_size: 1
-  options:
-#    use_activesupport_time_zone: true
-#    belongs_to_required_by_default: false
+  database: publisher_test
+  username: publisher
+  password: publisher
+  url: <%= ENV["TEST_DATABASE_URL"] %>
 
 # set these environment variables on your prod server
 production:
   clients:
     default:
-      uri: <%= ENV['MONGODB_URI'] %>
+      uri: <%= ENV['DATABASE_URL'] %>
   options:
 #    use_activesupport_time_zone: true
   #    belongs_to_required_by_default: false
\ No newline at end of file
diff --git a/db/migrate/20250212162143_create_user.rb b/db/migrate/20250212162143_create_user.rb
new file mode 100644
index 000000000..67ce08f62
--- /dev/null
+++ b/db/migrate/20250212162143_create_user.rb
@@ -0,0 +1,17 @@
+class CreateUser < ActiveRecord::Migration[7.1]
+  def change
+    create_table :users do |t|
+      t.string   :name
+      t.string   :email
+      t.string   :uid
+      t.string   :organisation_slug
+      t.string   :organisation_content_id
+      t.string   :app_name
+      t.string   :permissions, array: true, default: []
+      t.boolean  :remotely_signed_out, default: false
+      t.boolean  :disabled, default: false
+      t.timestamps
+      t.index :disabled
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
new file mode 100644
index 000000000..a2a28821b
--- /dev/null
+++ b/db/schema.rb
@@ -0,0 +1,32 @@
+# This file is auto-generated from the current state of the database. Instead
+# of editing this file, please use the migrations feature of Active Record to
+# incrementally modify your database, and then regenerate this schema definition.
+#
+# This file is the source Rails uses to define your schema when running `bin/rails
+# db:schema:load`. When creating a new database, `bin/rails db:schema:load` tends to
+# be faster and is potentially less error prone than running all of your
+# migrations from scratch. Old migrations may fail to apply correctly if those
+# migrations use external dependencies or application code.
+#
+# It's strongly recommended that you check this file into your version control system.
+
+ActiveRecord::Schema[7.1].define(version: 2025_02_12_162143) do
+  # These are extensions that must be enabled in order to support this database
+  enable_extension "plpgsql"
+
+  create_table "users", force: :cascade do |t|
+    t.string "name"
+    t.string "email"
+    t.string "uid"
+    t.string "organisation_slug"
+    t.string "organisation_content_id"
+    t.string "app_name"
+    t.string "permissions", default: [], array: true
+    t.boolean "remotely_signed_out", default: false
+    t.boolean "disabled", default: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["disabled"], name: "index_users_on_disabled"
+  end
+
+end
diff --git a/db/seeds/user.rb b/db/seeds/user.rb
index 119c58da3..29dc30d02 100644
--- a/db/seeds/user.rb
+++ b/db/seeds/user.rb
@@ -1,10 +1,8 @@
 if User.where(name: "Test user").blank?
   gds_organisation_id = "af07d5a5-df63-4ddc-9383-6a666845ebe9"
-  user_id = SecureRandom.uuid
 
   User.create!(
     name: "Test user",
-    uid: user_id,
     permissions: %w[signin govuk_editor skip_review],
     organisation_content_id: gds_organisation_id,
   )
diff --git a/test/functional/event_mailer_test.rb b/test/functional/event_mailer_test.rb
index 972e584d7..de246711a 100644
--- a/test/functional/event_mailer_test.rb
+++ b/test/functional/event_mailer_test.rb
@@ -17,6 +17,7 @@ def fact_check_email
   def action_email(action_name)
     guide = FactoryBot.create(:guide_edition, title: "Test Guide 2")
     requester = User.new(name: "Testing Person")
+    requester.save!
     action = guide.actions.create!(request_type: action_name, requester:)
     EventMailer.any_action(action, ["fake@not-a-real-email-address"])
   end
diff --git a/test/functional/event_notifications_test.rb b/test/functional/event_notifications_test.rb
index 35b01cb98..7bb5c1349 100644
--- a/test/functional/event_notifications_test.rb
+++ b/test/functional/event_notifications_test.rb
@@ -11,6 +11,7 @@ def fact_check_email
   def action_email(action)
     guide = FactoryBot.create(:guide_edition, title: "Test Guide 2")
     requester = User.new(name: "Testing Person")
+    requester.save!
     action = guide.actions.create!(request_type: action, requester:)
     EventNotifierService.any_action(action)
   end
diff --git a/test/legacy_integration_test_helper.rb b/test/legacy_integration_test_helper.rb
index 5820d1069..0e9967907 100644
--- a/test/legacy_integration_test_helper.rb
+++ b/test/legacy_integration_test_helper.rb
@@ -10,11 +10,15 @@ class LegacyIntegrationTest < ActionDispatch::IntegrationTest
   include Warden::Test::Helpers
 
   setup do
+    DatabaseCleaner[:mongoid].start
+    DatabaseCleaner.start
     test_strategy = Flipflop::FeatureSet.current.test!
     test_strategy.switch!(:design_system_edit, false)
   end
 
   teardown do
+    DatabaseCleaner[:mongoid].clean
+    DatabaseCleaner.clean
     Capybara.reset_sessions! # Forget the (simulated) browser state
     Capybara.use_default_driver # Revert Capybara.current_driver to Capybara.default_driver
     GDS::SSO.test_user = nil
diff --git a/test/models/user_test.rb b/test/models/user_test.rb
index f0ddeb71e..62ea48c1d 100644
--- a/test/models/user_test.rb
+++ b/test/models/user_test.rb
@@ -75,7 +75,7 @@ def setup
   test "should return enabled users" do
     disabled = FactoryBot.create(:user, disabled: true)
 
-    FactoryBot.create(:user).unset(:disabled)
+    FactoryBot.create(:user, disabled: false)
     FactoryBot.create(:user, disabled: false)
     FactoryBot.create(:user, disabled: nil)
 
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 759020e18..f6c374abc 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,5 +1,4 @@
 ENV["RAILS_ENV"] = "test"
-
 # Must go at top of file
 require "simplecov"
 SimpleCov.start
@@ -10,6 +9,7 @@
 require "minitest/autorun"
 require "mocha/minitest"
 require "database_cleaner/mongoid"
+require "database_cleaner/active_record"
 require "webmock/minitest"
 require "gds_api/test_helpers/publishing_api"
 require "support/tag_test_helpers"
@@ -27,8 +27,11 @@
 
 WebMock.disable_net_connect!(allow_localhost: true)
 
-DatabaseCleaner.strategy = :deletion
+DatabaseCleaner[:mongoid].strategy = :deletion
 # initial clean
+DatabaseCleaner[:mongoid].clean
+DatabaseCleaner.allow_remote_database_url = true
+DatabaseCleaner.strategy = :deletion
 DatabaseCleaner.clean
 
 Rails.application.load_tasks if Rake::Task.tasks.empty?
@@ -46,16 +49,18 @@ class ActiveSupport::TestCase
   include WebMock::API
   include GovukSchemas::AssertMatchers
 
-  def clean_db
-    DatabaseCleaner.clean
-  end
-  set_callback :teardown, :after, :clean_db
-
   setup do
+    DatabaseCleaner[:mongoid].start
+    DatabaseCleaner.start
     Sidekiq::Testing.inline!
     stub_any_publishing_api_call
   end
 
+  teardown do
+    DatabaseCleaner[:mongoid].clean
+    DatabaseCleaner.clean
+  end
+
   def without_metadata_denormalisation(*klasses, &_block)
     klasses.each { |klass| klass.any_instance.stubs(:denormalise_metadata).returns(true) }
     result = yield
diff --git a/test/unit/helpers/admin/publications_table_helper_test.rb b/test/unit/helpers/admin/publications_table_helper_test.rb
index 44be3f879..011cb8a26 100644
--- a/test/unit/helpers/admin/publications_table_helper_test.rb
+++ b/test/unit/helpers/admin/publications_table_helper_test.rb
@@ -176,11 +176,12 @@ class PublicationsTableHelperTest < ActionView::TestCase
 
     should "return a form for claiming a review when an edition assigned to another user is in review and has not been claimed and the current user may do so" do
       current_user = FactoryBot.create(:user, name: "David Cameron", permissions: %w[govuk_editor])
+      another_user = FactoryBot.create(:user, name: "Another User", permissions: %w[govuk_editor])
       edition = FactoryBot.create(
         :edition,
         state: "in_review",
         review_requested_at: "2024-07-12",
-        assigned_to_id: "66911dbf2c88ee0001d8af62",
+        assigned_to_id: another_user.id,
       )
 
       assert_includes reviewer(edition, current_user), '<button class="gem-c-button govuk-button" type="submit">Claim 2i</button>'
@@ -188,11 +189,12 @@ class PublicationsTableHelperTest < ActionView::TestCase
 
     should "return nil when an edition assigned to another user is in review and has not been claimed and the current user may not do so" do
       current_user = FactoryBot.create(:user, name: "Gordon Brown")
+      another_user = FactoryBot.create(:user, name: "Another User")
       edition = FactoryBot.create(
         :edition,
         state: "in_review",
         review_requested_at: "2024-07-12",
-        assigned_to_id: "66911dbf2c88ee0001d8af62",
+        assigned_to_id: another_user.id,
       )
 
       assert_nil reviewer(edition, current_user)
diff --git a/test/unit/presenters/filtered_editions_presenter_test.rb b/test/unit/presenters/filtered_editions_presenter_test.rb
index 1f2f4da82..80e60917d 100644
--- a/test/unit/presenters/filtered_editions_presenter_test.rb
+++ b/test/unit/presenters/filtered_editions_presenter_test.rb
@@ -84,7 +84,8 @@ def a_gds_user
 
     should "filter by 'assigned to'" do
       anna = FactoryBot.create(:user, name: "Anna")
-      assigned_to_anna = FactoryBot.create(:guide_edition, assigned_to: anna.id)
+      # reference: note_for_postgres_migration
+      assigned_to_anna = FactoryBot.create(:guide_edition, assigned_to_id: anna.id)
       FactoryBot.create(:guide_edition)
 
       filtered_editions = FilteredEditionsPresenter.new(a_gds_user, assigned_to_filter: anna.id).editions
@@ -94,7 +95,8 @@ def a_gds_user
 
     should "filter by 'not assigned'" do
       anna = FactoryBot.create(:user, name: "Anna")
-      FactoryBot.create(:guide_edition, assigned_to: anna.id)
+      # reference: note_for_postgres_migration
+      FactoryBot.create(:guide_edition, assigned_to_id: anna.id)
       not_assigned = FactoryBot.create(:guide_edition)
 
       filtered_editions = FilteredEditionsPresenter.new(a_gds_user, assigned_to_filter: "nobody").editions
@@ -104,7 +106,8 @@ def a_gds_user
 
     should "ignore invalid 'assigned to'" do
       anna = FactoryBot.create(:user, name: "Anna")
-      FactoryBot.create(:guide_edition, assigned_to: anna.id)
+      # reference: note_for_postgres_migration
+      FactoryBot.create(:guide_edition, assigned_to_id: anna.id)
       FactoryBot.create(:guide_edition)
 
       filtered_editions =
@@ -288,4 +291,11 @@ def a_gds_user
       assert_not_includes users.map { |user| user[:text] }, disabled_user.name
     end
   end
+
+  def note_for_postgres_migration
+    # Temp-to-be-brought-back:
+    # Currently we are using assigned_to_id as a field to store the assigned_to_id
+    # to bypass the issue of having a belongs_to between a postgres table and a mongo table
+    # we will most likely bring back the belongs_to relationship once we move edition table to postgres.
+  end
 end