feat: add TransactionMetaPlugin to save comments when applicable

src/wutta_continuum/conf.py

@@ -28,7 +28,7 @@ import socket
 
 from sqlalchemy.orm import configure_mappers
 from sqlalchemy_continuum import make_versioned
-from sqlalchemy_continuum.plugins import Plugin
+from sqlalchemy_continuum.plugins import Plugin, TransactionMetaPlugin
 
 from wuttjamaican.conf import WuttaConfigExtension
 from wuttjamaican.util import load_object
@@ -66,6 +66,20 @@ class WuttaContinuumConfigExtension(WuttaConfigExtension):
 
         For more about SQLAlchemy-Continuum see
         :doc:`sqlalchemy-continuum:intro`.
+
+        Two plugins are provided to ``make_versioned()``:
+
+        The first is ``TransactionMetaPlugin`` for sake of adding
+        comments (see
+        :mod:`~sqlalchemy-continuum:sqlalchemy_continuum.plugins.transaction_meta`).
+
+        The second by default is :class:`WuttaContinuumPlugin` but you
+        can override with config:
+
+        .. code-block:: ini
+
+           [wutta_continuum]
+           wutta_plugin_spec = poser.db.continuum:PoserContinuumPlugin
         """
         # only do this if config enables it
         if not config.get_bool(
@@ -86,7 +100,7 @@ class WuttaContinuumConfigExtension(WuttaConfigExtension):
             raise RuntimeError("something not right, app already has model")
 
         # let sqlalchemy-continuum do its thing
-        make_versioned(plugins=[plugin()])
+        make_versioned(plugins=[TransactionMetaPlugin(), plugin()])
 
         # must load model *between* prev and next calls
         app.get_model()
@@ -148,3 +162,16 @@ class WuttaContinuumPlugin(Plugin):
             kwargs["user_id"] = user_id
 
         return kwargs
+
+    def before_flush(self, uow, session):
+        """
+        We use this hook to inject the "comment" for current
+        transaction, if applicable.
+
+        This checks the session for the comment; so any session can
+        specify one like so::
+
+           session.info["continuum_comment"] = "hello world"
+        """
+        if comment := session.info.get("continuum_comment"):
+            uow.current_transaction.meta["comment"] = comment