Override the CORE-API -> Rattail Demo importer for Store data

this lets the demo have random extra Store records and the importer will just
ignore them

rattail_demo/importing/corepos_api.py

@@ -0,0 +1,31 @@
+# -*- coding: utf-8; -*-
+"""
+CORE-POS API -> Rattail Demo importing
+"""
+
+from rattail_corepos.importing.corepos import api as base
+
+
+class FromCOREPOSToRattail(base.FromCOREPOSToRattail):
+    """
+    Override some parts of CORE-POS API -> Rattail importing.
+    """
+
+    def get_importers(self):
+        importers = super(FromCOREPOSToRattail, self).get_importers()
+        importers['Store'] = StoreImporter
+        return importers
+
+
+class StoreImporter(base.StoreImporter):
+    """
+    Tweak how we import Store data from CORE-POS API.
+    """
+
+    def cache_query(self):
+        model = self.model
+        # we ignore any Store records which are not associated with CORE, so
+        # the importer will never be tempted to delete them etc.
+        return self.session.query(model.Store)\
+                           .join(model.CoreStore)\
+                           .filter(model.CoreStore.corepos_id != None)