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| author | Mike Bayer <mike_mp@zzzcomputing.com> | 2017-09-26 11:03:07 -0400 |
|---|---|---|
| committer | Mike Bayer <mike_mp@zzzcomputing.com> | 2017-09-26 11:36:08 -0400 |
| commit | ec1700ba29f7f15859ee6576855a4d6675265640 (patch) | |
| tree | 2b2f19bbcc5906139a1b88c527d46e64eceaf4bd /lib/sqlalchemy/ext/declarative/api.py | |
| parent | 1b0b35f254f545dbeb3ad6e2215ba24ae1c02894 (diff) | |
| download | sqlalchemy-ticket_4091.tar.gz | |
Warnings for @declared_attr.cascadingticket_4091
A warning is emitted if a subclass attempts to override an attribute
that was declared on a superclass using ``@declared_attr.cascading``
that the overridden attribute will be ignored. This use
case cannot be fully supported down to further subclasses without more
complex development efforts, so for consistency the "cascading" is
honored all the way down regardless of overriding attributes.
A warning is emitted if the ``@declared_attr.cascading`` attribute is
used with a special declarative name such as ``__tablename__``, as this
has no effect.
Ensure that documenation refers to the current inconsistency that
__tablename__ can be overridden by subclasses however
@declared_attr.cascading cannot.
Fixes: #4091
Fixes: #4092
Change-Id: I3aecdb2f99d408e404a1223f5ad86ae3c7fdf036
Diffstat (limited to 'lib/sqlalchemy/ext/declarative/api.py')
| -rw-r--r-- | lib/sqlalchemy/ext/declarative/api.py | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/lib/sqlalchemy/ext/declarative/api.py b/lib/sqlalchemy/ext/declarative/api.py index ee13a90f3..0773922d0 100644 --- a/lib/sqlalchemy/ext/declarative/api.py +++ b/lib/sqlalchemy/ext/declarative/api.py @@ -199,11 +199,24 @@ class declared_attr(interfaces._MappedAttribute, property): or MapperProperty-based declared attribute should be configured distinctly per mapped subclass, within a mapped-inheritance scenario. - .. note:: + .. warning:: - The :attr:`.declared_attr.cascading` modifier **only** applies - to the use of :class:`.declared_attr` on declarative mixin classes - and ``__abstract__`` classes. + The :attr:`.declared_attr.cascading` modifier has several + limitations: + + * The flag **only** applies to the use of :class:`.declared_attr` + on declarative mixin classes and ``__abstract__`` classes; it + currently has no effect when used on a mapped class directly. + + * The flag **only** applies to normally-named attributes, e.g. + not any special underscore attributes such as ``__tablename__``. + On these attributes it has **no** effect. + + * The flag currently **does not allow further overrides** down + the class hierarchy; if a subclass tries to override the + attribute, a warning is emitted and the overridden attribute + is skipped. This is a limitation that it is hoped will be + resolved at some point. Below, both MyClass as well as MySubClass will have a distinct ``id`` Column object established:: |