Merge branch 'master' of https://github.com/rails/rails

1 files changed, 60 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/associations/preloader/has_and_belongs_to_many.rb b/activerecord/lib/active_record/associations/preloader/has_and_belongs_to_many.rb
new file mode 100644
index 0000000000..24be279449
--- /dev/null
+++ b/activerecord/lib/active_record/associations/preloader/has_and_belongs_to_many.rb
@@ -0,0 +1,60 @@
+module ActiveRecord
+  module Associations
+    class Preloader
+      class HasAndBelongsToMany < CollectionAssociation #:nodoc:
+        attr_reader :join_table
+
+        def initialize(klass, records, reflection, preload_options)
+          super
+          @join_table = Arel::Table.new(options[:join_table]).alias('t0')
+        end
+
+        # Unlike the other associations, we want to get a raw array of rows so that we can
+        # access the aliased column on the join table
+        def records_for(ids)
+          scope = super
+          klass.connection.select_all(scope.arel.to_sql, 'SQL', scope.bind_values)
+        end
+
+        def owner_key_name
+          reflection.active_record_primary_key
+        end
+
+        def association_key_name
+          'ar_association_key_name'
+        end
+
+        def association_key
+          join_table[reflection.foreign_key]
+        end
+
+        private
+
+        # Once we have used the join table column (in super), we manually instantiate the
+        # actual records, ensuring that we don't create more than one instances of the same
+        # record
+        def associated_records_by_owner
+          records = {}
+          super.each do |owner_key, rows|
+            rows.map! { |row| records[row[klass.primary_key]] ||= klass.instantiate(row) }
+          end
+        end
+
+        def build_scope
+          super.joins(join).select(join_select)
+        end
+
+        def join_select
+          association_key.as(Arel.sql(association_key_name))
+        end
+
+        def join
+          condition = table[reflection.association_primary_key].eq(
+            join_table[reflection.association_foreign_key])
+
+          table.create_join(join_table, table.create_on(condition))
+        end
+      end
+    end
+  end
+end