Cannot use classproperty for class attributes

[Former user]

Well, there is a simple usecase:

class MyHistoryMixin:
    @classproperty
    def __tablename__(cls):
        return cls.parent_name + '_changelog'

class MyModel(Base, MyHistoryMixin):
    parent_name = 'foo'

gives me that traceback:

Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/nose/case.py", line 183, in runTest
    self.test(*self.arg)
  File "/home/ente/Projects/sqlalchemy/test/ext/test_declarative.py", line 1938, in test_table_name_inhertited_from_property
    class MyModel(Base, MyHistoryMixin):
  File "/home/ente/Projects/sqlalchemy/lib/sqlalchemy/ext/declarative.py", line 712, in __init__
    _as_declarative(cls, classname, cls.__dict__)
  File "/home/ente/Projects/sqlalchemy/lib/sqlalchemy/ext/declarative.py", line 656, in _as_declarative
    "specified and does not inherit from an existing table-mapped class." % cls
InvalidRequestError: Class <class 'test.ext.test_declarative.MyModel'> does not have a __table__ or __tablename__ specified and does not inherit from an existing table-mapped class.

I just already created a testcase for that: http://paste.pocoo.org/show/194202/

I guess SQLAlchemy is doing something wrong here, since it works properly on other classes not using sqlalchemy stuff.

Would be cool if something like that is possible.

Regards, Christopher.

[Mike Bayer]

this is the likely patch:

--- a/lib/sqlalchemy/ext/declarative.py Fri Mar 26 13:48:13 2010 -0400
+++ b/lib/sqlalchemy/ext/declarative.py Fri Mar 26 13:58:05 2010 -0400
@@ -548,9 +548,9 @@
                 obj = getattr(base,name, None)
                 if isinstance(obj, Column):
                     dict_[name](name)=column_copies[obj](obj)=obj.copy()
-            get_mapper_args = get_mapper_args or getattr(base,'__mapper_args__',None)
-            get_table_args = get_table_args or getattr(base,'__table_args__',None)
-            tablename = getattr(base,'__tablename__',None)
+            get_mapper_args = get_mapper_args or getattr(cls,'__mapper_args__',None)
+            get_table_args = get_table_args or getattr(cls,'__table_args__',None)
+            tablename = getattr(cls,'__tablename__',None)
             if tablename:
                 # subtle: if tablename is a descriptor here, we actually
                 # put the wrong value in, but it serves as a marker to get

[Mike Bayer]

this is a refinement of that patch. but I'm still not remembering why we have to dance around cls.foo as much as we are here.

--- a/lib/sqlalchemy/ext/declarative.py Fri Mar 26 13:48:13 2010 -0400
+++ b/lib/sqlalchemy/ext/declarative.py Fri Mar 26 14:12:14 2010 -0400
@@ -531,31 +531,32 @@

 def _as_declarative(cls, classname, dict_):

-    # doing it this way enables these attributes to be descriptors,
-    # see below...
-    get_mapper_args = '__mapper_args__' in dict_
-    get_table_args = '__table_args__' in dict_
-    
     # dict_ will be a dictproxy, which we can't write to, and we need to!
     dict_ = dict(dict_)

     column_copies = dict()
-
+    unmapped_mixins = False
     for base in cls.__bases__:
         names = dir(base)
         if not _is_mapped_class(base):
+            unmapped_mixins = True
             for name in names:
                 obj = getattr(base,name, None)
                 if isinstance(obj, Column):
                     dict_[name](name)=column_copies[obj](obj)=obj.copy()
-            get_mapper_args = get_mapper_args or getattr(base,'__mapper_args__',None)
-            get_table_args = get_table_args or getattr(base,'__table_args__',None)
-            tablename = getattr(base,'__tablename__',None)
-            if tablename:
-                # subtle: if tablename is a descriptor here, we actually
-                # put the wrong value in, but it serves as a marker to get
-                # the right value value...
-                dict_['__tablename__']('__tablename__')=tablename
+
+    # doing it this way enables these attributes to be descriptors
+    get_mapper_args = '__mapper_args__' in dict_
+    get_table_args = '__table_args__' in dict_
+    if unmapped_mixins:
+        get_mapper_args = get_mapper_args or getattr(cls,'__mapper_args__',None)
+        get_table_args = get_table_args or getattr(cls,'__table_args__',None)
+        tablename = getattr(cls,'__tablename__',None)
+        if tablename:
+            # subtle: if tablename is a descriptor here, we actually
+            # put the wrong value in, but it serves as a marker to get
+            # the right value value...
+            dict_['__tablename__']('__tablename__')=tablename

     # now that we know whether or not to get these, get them from the class
     # if we should, enabling them to be decorators

[Mike Bayer]

it appears uncontroversial. 15159a844d11b4a081bea4d7f6e3e3cf7dec937d

[Mike Bayer]

Removing milestone: 0.6.0 (automated comment)