Lazily add `Aggregations` to `composed_of` models

`composed_of` is a fairly rare method to call on models.  This commit
adds the `Aggregations` module to models that call `composed_of` so that
models that *don't* call `composed_of` don't need to instantiate the
`aggregation_cache` hash.  This saves one hash allocation per model
instance that doesn't use `composed_of`

2 files changed, 5 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/aggregations.rb b/activerecord/lib/active_record/aggregations.rb
index 27a641f05b..7286837ac7 100644
--- a/activerecord/lib/active_record/aggregations.rb
+++ b/activerecord/lib/active_record/aggregations.rb
@@ -225,6 +225,10 @@ module ActiveRecord
         def composed_of(part_id, options = {})
           options.assert_valid_keys(:class_name, :mapping, :allow_nil, :constructor, :converter)
 
+          unless self < Aggregations
+            include Aggregations
+          end
+
           name        = part_id.id2name
           class_name  = options[:class_name]  || name.camelize
           mapping     = options[:mapping]     || [ name, name ]
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 7ab9160265..5169f312f5 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -288,6 +288,7 @@ module ActiveRecord #:nodoc:
     extend Enum
     extend Delegation::DelegateCache
     extend CollectionCacheKey
+    extend Aggregations::ClassMethods
 
     include Core
     include DatabaseConfigurations
@@ -314,7 +315,6 @@ module ActiveRecord #:nodoc:
     include ActiveModel::SecurePassword
     include AutosaveAssociation
     include NestedAttributes
-    include Aggregations
     include Transactions
     include TouchLater
     include NoTouching