old_contents: from django.conf import settings
  from django.db.models.aggregates import Sum
  from django.db.models.sql.aggregates import Sum as BaseSQLSum
  
  
  class SQLSum(BaseSQLSum):
      @property
      def sql_template(self):
          if settings.DATABASES['default']['ENGINE'] == \
                  'django.db.backends.postgresql_psycopg2':
              return '%(function)s(%(field)s::int)'
          return '%(function)s(%(field)s)'
  
  
  class BooleanSum(Sum):
      function = None
  
      def add_to_query(self, query, alias, col, source, is_summary):
          aggregate = SQLSum(col, source=source, is_summary=is_summary,
                             **self.extra)
          query.aggregates[alias] = aggregate
  
new_contents: from django.conf import settings
  from django.db.models.aggregates import Sum
  
  
  class SQLSum(Sum):
      @property
      def sql_template(self):
          if settings.DATABASES['default']['ENGINE'] == \
                  'django.db.backends.postgresql_psycopg2':
              return '%(function)s(%(field)s::int)'
          return '%(function)s(%(field)s)'
  
  
  class BooleanSum(Sum):
      def add_to_query(self, query, alias, col, source, is_summary):
          aggregate = SQLSum(col, source=source, is_summary=is_summary,
                             **self.extra)
          query.aggregates[alias] = aggregate
  
subject: Add support for Django 1.10+