Add cache_model() method to app handler

also make cache_model() always return an OrderedDict, in case the
ordering actually matters to caller

rattail/app.py

@@ -135,6 +135,15 @@ class AppHandler(object):
         from rattail.db import Session
         return Session(**kwargs)
 
+    def cache_model(self, session, model, **kwargs):
+        """
+        Convenience method which invokes
+        :func:`rattail.db.cache.cache_model()` with the given model
+        and keyword arguments.
+        """
+        from rattail.db import cache
+        return cache.cache_model(session, model, **kwargs)
+
     def make_temp_dir(self, **kwargs):
         """
         Create a temporary directory.  This is mostly a convenience wrapper
@@ -258,8 +267,7 @@ class GenericHandler(object):
         Convenience method which invokes :func:`rattail.db.cache.cache_model()`
         with the given model and keyword arguments.
         """
-        from rattail.db import cache
-        return cache.cache_model(session, model, **kwargs)
+        return self.app.cache_model(session, model, **kwargs)
 
 
 def make_app(config, **kwargs):

rattail/db/cache.py

@@ -2,7 +2,7 @@
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2018 Lance Edgar
+#  Copyright © 2010-2021 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -33,6 +33,7 @@ from sqlalchemy.orm import joinedload
 
 from rattail.core import Object
 from rattail.db import model
+from rattail.util import OrderedDict
 
 
 log = logging.getLogger(__name__)
@@ -88,7 +89,7 @@ class ModelCacher(object):
         return q
 
     def get_cache(self, progress):
-        self.instances = {}
+        self.instances = OrderedDict()
         query = self.query()
         count = query.count()
         if not count: