add PackageBase SQLAlchemy ORM model

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/db.py

@@ -1,5 +1,7 @@
 import math
 
+from sqlalchemy.orm import backref, relationship
+
 import aurweb.config
 import aurweb.util
 
@@ -51,6 +53,11 @@ def make_random_value(table: str, column: str):
     return string
 
 
+def make_relationship(model, foreign_key, backref_):
+    return relationship(model, foreign_keys=[foreign_key],
+                        backref=backref(backref_, lazy="dynamic"))
+
+
 def query(model, *args, **kwargs):
     return session.query(model).filter(*args, **kwargs)