Add raise/raiseload relationship loading strategypr/193

- available via `lazy='raise'` or by setting the `raiseload` strategy
  via `options()`
- behaves almost like `lazy='noload'`, but instead of returning `None`
  it raises `InvalidRequestError`
- based on code from Mike Bayer that was posted to the sqlalchemy
  mailing list: https://groups.google.com/forum/#!topic/sqlalchemy/X_wA8K97smE

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index da0730f46..251930873 100644
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -524,6 +524,10 @@ class RelationshipProperty(StrategizedProperty):
             support "write-only" attributes, or attributes which are
             populated in some manner specific to the application.
 
+          * ``raise`` - no loading should occur at any time, and accessing
+            the attribute will fail with an
+            :exc:`~sqlalchemy.exc.InvalidRequestError`.
+
           * ``dynamic`` - the attribute will return a pre-configured
             :class:`.Query` object for all read
             operations, onto which further filtering operations can be