Do all version table writes in one commit

The behaviour of stacking the version decorators does not work as
expected.

What you would expect to happen is that each decorator causes a history
row to be written for its respective model object.

What actually happens is that the first decorator adds history records
to the database session, but then causes the database session to commit.
This means that subsequent uses of this decorator find a clean session,
and therefore no changes to copy to their respective history tables.

This commit changes the intended use of the decorator so that it is only
used once per function, and accepts multiple definitions of what to
record history for. This way it can record everything that needs to go
into the history before doing anything that would risk flushing the
session.

app/dao/dao_utils.py

@@ -1,5 +1,5 @@
 import itertools
-from functools import wraps, partial
+from functools import wraps
 
 from app import db
 from app.history_meta import create_history
@@ -20,8 +20,18 @@ def transactional(func):
     return commit_or_rollback
 
 
-def version_class(model_class, history_cls=None, must_write_history=True):
-    create_hist = partial(create_history, history_cls=history_cls)
+class VersionOptions():
+
+    def __init__(self, model_class, history_class=None, must_write_history=True):
+        self.model_class = model_class
+        self.history_class = history_class
+        self.must_write_history = must_write_history
+
+
+def version_class(*version_options):
+
+    if len(version_options) == 1 and not isinstance(version_options[0], VersionOptions):
+        version_options = (VersionOptions(version_options[0]),)
 
     def versioned(func):
         @wraps(func)
@@ -29,20 +39,35 @@ def version_class(model_class, history_cls=None, must_write_history=True):
 
             func(*args, **kwargs)
 
-            history_objects = [create_hist(obj) for obj in
-                               itertools.chain(db.session.new, db.session.dirty)
-                               if isinstance(obj, model_class)]
+            session_objects = []
 
-            if history_objects == [] and must_write_history:
-                raise RuntimeError((
-                    'Can\'t record history for {} '
-                    '(something in your code has casued the database to '
-                    'flush the session early so there\'s nothing to '
-                    'copy into the history table)'
-                ).format(model_class.__name__))
+            for version_option in version_options:
+                tmp_session_objects = [
+                    (
+                        session_object, version_option.history_class
+                    )
+                    for session_object in itertools.chain(
+                        db.session.new, db.session.dirty
+                    )
+                    if isinstance(
+                        session_object, version_option.model_class
+                    )
+                ]
 
-            for h_obj in history_objects:
-                db.session.add(h_obj)
+                if tmp_session_objects == [] and version_option.must_write_history:
+                    raise RuntimeError((
+                        'Can\'t record history for {} '
+                        '(something in your code has casued the database to '
+                        'flush the session early so there\'s nothing to '
+                        'copy into the history table)'
+                    ).format(version_option.model_class.__name__))
+
+                session_objects += tmp_session_objects
+
+            for session_object, history_class in session_objects:
+                db.session.add(
+                    create_history(session_object, history_cls=history_class)
+                )
 
         return record_version
     return versioned