Added a guard to prevent duplicate starter data.

diner_installer.py

@@ -2,7 +2,11 @@ from sys import stderr
 
 from sqlalchemy.exc import SQLAlchemyError
 
-from diner import DinerDatabase, Menu, Item, Order, OrderItem
+from diner import DinerDatabase, Persisted, Menu, Item, Order, OrderItem
+
+
+def already_has_data(session):
+    return any(session.query(table).first() is not None for table in Persisted.metadata.sorted_tables)
 
 
 def add_starter_data(session):
@@ -27,9 +31,12 @@ def main():
         diner_database.ensure_tables_exist()
         print('Tables created.')
         # session = diner_database.create_session()
-        # add_starter_data(session)
-        # session.commit()
-        # print('Records created.')
+        # if already_has_data(session):
+        #     print('Not creating records because some already exist.')
+        # else:
+        #     add_starter_data(session)
+        #     session.commit()
+        #     print('Records created.')
     except SQLAlchemyError as exception:
         print('Database setup failed!', file=stderr)
         print(f'Cause: {exception}', file=stderr)