Merge pull request #85 from postatum/103410068_update_events

Update set_field_value usage docs

docs/source/event_handlers.rst

@@ -80,7 +80,7 @@ Before vs After
 ``Before`` events should be used to:
     * Transform input
     * Perform validation
-    * Apply changes to object that is being affected by the request using the ``event.set_field_value`` method
+    * Apply changes to object that is being affected by the request using the ``event.set_field_value`` method. Note that if field you change by calling ``event.set_field_value`` is not affected by request, it will be added to ``event.fields`` which will makes field processors which are connected to this field to be triggered, if they are run after this method call(connected to events after handler that performs method call).
 
 ``After`` events should be used to:
     * Change DB objects which are not affected by the request

docs/source/field_validators.rst

@@ -109,3 +109,7 @@ To edit other fields of instance, ``event.set_field_value`` method should be use
         event = kwargs['event']
         event.set_field_value('days_left', days_left)
         return kwargs['new_value']
+
+Note that if field you change by calling ``event.set_field_value`` is not affected by request, it will be added to ``event.fields`` which will makes field processors which are connected to changed field to be triggered, if they are run after this method call(connected to events after handler that performs method call).
+
+E.g. if in addition to above ``calculate_days_left`` processor we had field processors for ``days_left`` field set up, running ``calculate_days_left`` will make ``days_left`` field processors run, because after ``event.set_field_value`` was called in ``calculate_days_left`` field ``days_left`` is considered "updated/changed".