Add writing_role configuration for database connection switching

README.md

@@ -121,6 +121,16 @@ Time zone objects also work. To see a list of available time zones in Rails, run
 
 See [date storage](#date-storage) for how dates are stored.
 
+### Multiple Databases
+
+Specify a `writing_role` when you want to explicitly switch the database role when writing the rollup to the database.
+
+```ruby
+Rollup.writing_role = :writing
+```
+
+See [ActiveRecord::Base.connected_to](https://guides.rubyonrails.org/active_record_multiple_databases.html#connecting-to-the-database) for more information.
+
 ### Calculations
 
 Rollups use `count` by default. For other calculations, use:

lib/rollup.rb

@@ -5,6 +5,7 @@ class Rollup < ActiveRecord::Base
 
   class << self
     attr_accessor :week_start
+    attr_accessor :writing_role
     attr_writer :time_zone
   end
   self.week_start = :sunday

lib/rollup/aggregator.rb

@@ -19,7 +19,9 @@ def rollup(name, column: nil, interval: "day", dimension_names: nil, time_zone:
       records = prepare_result(result, name, dimension_names, interval)
 
       maybe_clear(clear, name, interval) do
-        save_records(records) if records.any?
+        with_writing_role do
+          save_records(records) if records.any?
+        end
       end
     end
 
@@ -184,6 +186,14 @@ def maybe_clear(clear, name, interval)
       end
     end
 
+    def with_writing_role(&block)
+      if Rollup.writing_role.present?
+        ActiveRecord::Base.connected_to(role: Rollup.writing_role, &block)
+      else
+        block.call
+      end
+    end
+
     def save_records(records)
       # order must match unique index
       # consider using index name instead

test/aggregator_test.rb

@@ -133,4 +133,37 @@ def test_range_current
     end
     assert_equal "Cannot use range and current together", error.message
   end
+
+  def test_writing_role_switching
+    connected_to_args = nil
+    ActiveRecord::Base.singleton_class.define_method(:connected_to) do |role:, &block|
+      connected_to_args = role
+      block.call
+    end
+
+    create_users
+    Rollup.writing_role = :writing
+    User.rollup("Test")
+
+    assert_equal :writing, connected_to_args, "Expected connected_to to be called with writing role"
+  ensure
+    ActiveRecord::Base.singleton_class.remove_method(:connected_to)
+    Rollup.writing_role = nil
+  end
+
+  def test_no_writing_role_switching
+    connected_to_called = false
+    ActiveRecord::Base.singleton_class.define_method(:connected_to) do |role:, &block|
+      connected_to_called = true
+      block.call
+    end
+
+    create_users
+    Rollup.writing_role = nil
+    User.rollup("Test")
+
+    refute connected_to_called, "Expected connected_to not to be called when writing_role is nil"
+  ensure
+    ActiveRecord::Base.singleton_class.remove_method(:connected_to)
+  end
 end