fix: add startup workaround for CORE model imports, to avoid error

still not 100% clear why this has started happening but clearly has
something to do with changes to wuttjamaican / rattail config startup
sequence..

tailbone_corepos/provider.py

@@ -2,7 +2,7 @@
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2023 Lance Edgar
+#  Copyright © 2010-2024 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -24,6 +24,7 @@
 Tailbone Provider for CORE-POS Integration
 """
 
+import sqlalchemy as sa
 from sqlalchemy.orm import sessionmaker, scoped_session
 from zope.sqlalchemy import register
 
@@ -71,6 +72,37 @@ class TailboneCorePosProvider(TailboneProvider):
                 register(Session)
                 ExtraCoreTransArchiveSessions[key] = Session
 
+        # must import all sqlalchemy models before things get rolling,
+        # otherwise can have errors about continuum TransactionMeta class
+        # not yet mapped, when relevant pages are first requested...
+        # cf. https://docs.pylonsproject.org/projects/pyramid_cookbook/en/latest/database/sqlalchemy.html#importing-all-sqlalchemy-models
+        # hat tip to https://stackoverflow.com/a/59241485
+        if rattail_config.core_office_op_engine:
+            app = rattail_config.get_app()
+            corepos = app.get_corepos_handler()
+
+            # nb. use fake db to avoid true cxn errors, since the only
+            # point of this is to load the models
+            engine = sa.create_engine('sqlite://')
+
+            # office_op
+            core_model = corepos.get_model_office_op()
+            core_session = corepos.make_session_office_op(bind=engine)
+            try:
+                core_session.query(core_model.Store).first()
+            except sa.exc.OperationalError:
+                pass
+            core_session.close()
+
+            # office_trans
+            core_model = corepos.get_model_office_trans()
+            core_session = corepos.make_session_office_trans(bind=engine)
+            try:
+                core_session.query(core_model.TransactionDetail).first()
+            except sa.exc.OperationalError:
+                pass
+            core_session.close()
+
     def get_provided_views(self):
         return {