diff options
Diffstat (limited to 'lib/sqlalchemy')
| -rw-r--r-- | lib/sqlalchemy/ext/declarative/api.py | 21 | ||||
| -rw-r--r-- | lib/sqlalchemy/ext/declarative/base.py | 39 |
2 files changed, 52 insertions, 8 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:: diff --git a/lib/sqlalchemy/ext/declarative/base.py b/lib/sqlalchemy/ext/declarative/base.py index 3a2ac66ae..255373597 100644 --- a/lib/sqlalchemy/ext/declarative/base.py +++ b/lib/sqlalchemy/ext/declarative/base.py @@ -88,6 +88,19 @@ def _as_declarative(cls, classname, dict_): _MapperConfig.setup_mapping(cls, classname, dict_) +def _check_declared_props_nocascade(obj, name, cls): + + if isinstance(obj, declarative_props): + if getattr(obj, '_cascading', False): + util.warn( + "@declared_attr.cascading is not supported on the %s " + "attribute on class %s. This attribute invokes for " + "subclasses in any case." % (name, cls)) + return True + else: + return False + + class _MapperConfig(object): @classmethod @@ -167,9 +180,11 @@ class _MapperConfig(object): for name, obj in vars(base).items(): if name == '__mapper_args__': + check_decl = \ + _check_declared_props_nocascade(obj, name, cls) if not mapper_args_fn and ( not class_mapped or - isinstance(obj, declarative_props) + check_decl ): # don't even invoke __mapper_args__ until # after we've determined everything about the @@ -177,17 +192,21 @@ class _MapperConfig(object): # make a copy of it so a class-level dictionary # is not overwritten when we update column-based # arguments. - mapper_args_fn = lambda: dict(cls.__mapper_args__) + mapper_args_fn = lambda: dict(cls.__mapper_args__) # noqa elif name == '__tablename__': + check_decl = \ + _check_declared_props_nocascade(obj, name, cls) if not tablename and ( not class_mapped or - isinstance(obj, declarative_props) + check_decl ): tablename = cls.__tablename__ elif name == '__table_args__': + check_decl = \ + _check_declared_props_nocascade(obj, name, cls) if not table_args and ( not class_mapped or - isinstance(obj, declarative_props) + check_decl ): table_args = cls.__table_args__ if not isinstance( @@ -220,6 +239,18 @@ class _MapperConfig(object): elif isinstance(obj, declarative_props): oldclassprop = isinstance(obj, util.classproperty) if not oldclassprop and obj._cascading: + if name in dict_: + # unfortunately, while we can use the user- + # defined attribute here to allow a clean + # override, if there's another + # subclass below then it still tries to use + # this. not sure if there is enough information + # here to add this as a feature later on. + util.warn( + "Attribute '%s' on class %s cannot be " + "processed due to " + "@declared_attr.cascading; " + "skipping" % (name, cls)) dict_[name] = column_copies[obj] = \ ret = obj.__get__(obj, cls) setattr(cls, name, ret) |