Add scope config option

Allow the entire backend to use translations only from a subset of
the translation records.

README.md

@@ -85,6 +85,16 @@ I18n::Backend::ActiveRecord.configure do |config|
 end
 ```
 
+The ActiveRecord backend can be configured to use a `scope` to isolate sets of translations. That way, two applications
+using the backend with the same database table can use translation data independently of one another.
+If configured with a scope, all data used will be limited to records with that particular scope identifier:
+
+```ruby
+I18n::Backend::ActiveRecord.configure do |config|
+  config.scope = 'app1' # defaults to nil, disabling scope
+end
+```
+
 ## Usage
 
 You can now use `I18n.t('Your String')` to lookup translations in the database.

lib/generators/i18n/active_record/templates/advanced_initializer.rb.erb

@@ -15,4 +15,5 @@ end
 I18n::Backend::ActiveRecord.configure do |config|
   # config.cache_translations = true # defaults to false
   # config.cleanup_with_destroy = true # defaults to false
+  # config.scope = 'app_scope' # defaults to nil, won't be used
 end

lib/generators/i18n/active_record/templates/migration.rb.erb

@@ -1,6 +1,7 @@
 class <%= migration_class_name %> < ActiveRecord::Migration[<%= ActiveRecord::Migration.current_version %>]
   def change
     create_table :<%= table_name %> do |t|
+      t.string :scope
       t.string :locale
       t.string :key
       t.text :value

lib/generators/i18n/active_record/templates/simple_initializer.rb.erb

@@ -4,4 +4,5 @@ I18n.backend = I18n::Backend::ActiveRecord.new
 I18n::Backend::ActiveRecord.configure do |config|
   # config.cache_translations = true # defaults to false
   # config.cleanup_with_destroy = true # defaults to false
+  # config.scope = 'app_scope' # defaults to nil, won't be used
 end

lib/i18n/backend/active_record/configuration.rb

@@ -4,11 +4,14 @@ module I18n
   module Backend
     class ActiveRecord
       class Configuration
-        attr_accessor :cleanup_with_destroy, :cache_translations
+        attr_accessor :cleanup_with_destroy,
+          :cache_translations,
+          :scope
 
         def initialize
           @cleanup_with_destroy = false
           @cache_translations = false
+          @scope = nil
         end
       end
     end

lib/i18n/backend/active_record/translation.rb

@@ -55,13 +55,24 @@ class Translation < ::ActiveRecord::Base
 
         serialize :value
         serialize :interpolations, Array
+        before_validation :set_scope
         after_commit :invalidate_translations_cache
 
+        default_scope { scoped }
+
         class << self
           def locale(locale)
             where(locale: locale.to_s)
           end
 
+          def scoped
+            if record_scope = ActiveRecord.config.scope
+              where(scope: record_scope)
+            else
+              all
+            end
+          end
+
           def lookup(keys, *separator)
             column_name = connection.quote_column_name('key')
             keys = Array(keys).map!(&:to_s)
@@ -123,6 +134,12 @@ def value=(value)
         def invalidate_translations_cache
           I18n.backend.reload! if I18n::Backend::ActiveRecord.config.cache_translations
         end
+
+        private
+
+          def set_scope
+            self.scope ||= ActiveRecord.config.scope if ActiveRecord.config.scope
+          end
       end
     end
   end

test/active_record_test.rb

@@ -172,4 +172,35 @@ def setup
       I18n.t('foo')
     end
   end
+
+  class ScopeTest < I18nBackendActiveRecordTest
+    def setup
+      super
+
+      I18n::Backend::ActiveRecord.config.scope = 'scope1'
+    end
+
+    test 'scope config option divides translations into isolated sets' do
+      store_translations(:en, foo: 'foo1')
+      assert_equal('foo1', I18n.t(:foo))
+
+      I18n::Backend::ActiveRecord.config.scope = 'scope2'
+      store_translations(:en, foo: 'foo2')
+      assert_equal('foo2', I18n.t(:foo))
+
+      I18n::Backend::ActiveRecord.config.scope = 'scope1'
+      assert_equal('foo1', I18n.t(:foo))
+    end
+
+    test 'scope config of nil disables scope' do
+      store_translations(:en, bar1: 'bar1')
+
+      I18n::Backend::ActiveRecord.config.scope = 'scope2'
+      store_translations(:en, bar2: 'bar2')
+
+      I18n::Backend::ActiveRecord.config.scope = nil
+      assert_equal('bar1', I18n.t(:bar1))
+      assert_equal('bar2', I18n.t(:bar2))
+    end
+  end
 end

test/test_helper.rb

@@ -40,13 +40,14 @@
   ::ActiveRecord::Migration.verbose = false
   ::ActiveRecord::Schema.define(version: 1) do
     create_table :translations, force: true do |t|
+      t.string :scope
       t.string :locale
       t.string :key
       t.text :value
       t.text :interpolations
       t.boolean :is_proc, default: false
     end
-    add_index :translations, %i[locale key], unique: true
+    add_index :translations, %i[scope locale key], unique: true
   end
 end