If I understand the problem correctly your best shot would be using sqlalchemy magical `hybrid_property` , hybrid_method, etc.
here: http://docs.sqlalchemy.org/ru/latest/orm/extensions/hybrid.html On Monday, March 18, 2013 9:20:15 PM UTC+2, millerdev wrote: > > Hi, > > Using declarative here, and I'm trying to create a column_property with a > correlated subquery that returns a count of records with a matching value > in some other column. Here's what I've tried. Option 1 is the best, option > 2 is ugly but second best, option 3 is not a good option since there are > many other classes involved and the place where I'd need to put that code > is far away from where it logically belongs. > > from sqlalchemy import * > from sqlalchemy.orm import * > from sqlalchemy.ext.declarative import * > from sqlalchemy.ext.declarative import declared_attr > > Base = declarative_base() > option = 1 > > class Foo(Base): > __tablename__ = 'foo' > id = Column(Integer, primary_key=True) > bar_id = Column(Integer, ForeignKey("bar.id")) > name = Column(String) > > if option == 1: > # does not work (see first traceback below) > @declared_attr > def name_count(cls): > clx = aliased(cls) > return column_property( > select(func.count([clx.id])) > .where(clx.name == cls.name) > .correlate(cls.__table__)) > > if option == 2: > # does not work (see second traceback below) > _foo = aliased(Foo) > Foo.name_count = column_property( > select([func.count(_foo.id)]) > .where(_foo.name == Foo.name) > .correlate(Foo.__table__)) > > > class Bar(Base): > __tablename__ = 'bar' > id = Column(Integer, primary_key=True) > name = Column(String) > > > if option == 3: > # works, but really not where I want to put this code > _foo = aliased(Foo) > Foo.name_count = column_property( > select([func.count(_foo.id)]) > .where(_foo.name == Foo.name) > .correlate(Foo.__table__)) > > > Option 1 traceback: > > Traceback (most recent call last): > File "temp/example.py", line 8, in <module> > class Foo(Base): > File ".../python2.7/site-packages/sqlalchemy/ext/declarative.py", line > 1348, in __init__ > _as_declarative(cls, classname, cls.__dict__) > File ".../python2.7/site-packages/sqlalchemy/ext/declarative.py", line > 1181, in _as_declarative > value = getattr(cls, k) > File ".../python2.7/site-packages/sqlalchemy/ext/declarative.py", line > 1554, in __get__ > return desc.fget(cls) > File "temp/example.py", line 15, in name_count > clx = aliased(cls) > File ".../python2.7/site-packages/sqlalchemy/orm/util.py", line 385, in > aliased > return AliasedClass(element, alias=alias, name=name, > adapt_on_names=adapt_on_names) > File ".../python2.7/site-packages/sqlalchemy/orm/util.py", line 298, in > __init__ > self.__mapper = _class_to_mapper(cls) > File ".../python2.7/site-packages/sqlalchemy/orm/util.py", line 673, in > _class_to_mapper > raise exc.UnmappedClassError(class_or_mapper) > sqlalchemy.orm.exc.UnmappedClassError: Class '__main__.Foo' is not mapped > > > Option 2 traceback: > > Traceback (most recent call last): > File "temp/example.py", line 16, in <module> > select([func.count(_foo.id)]) > File ".../python2.7/site-packages/sqlalchemy/sql/expression.py", line > 1229, in __call__ > return func(*c, **o) > File ".../python2.7/site-packages/sqlalchemy/sql/functions.py", line 16, > in __call__ > args = [_literal_as_binds(c) for c in args] > File ".../python2.7/site-packages/sqlalchemy/sql/expression.py", line > 1440, in _literal_as_binds > return element.__clause_element__() > File ".../python2.7/site-packages/sqlalchemy/orm/attributes.py", line > 117, in __clause_element__ > return self.comparator.__clause_element__() > File ".../python2.7/site-packages/sqlalchemy/util/langhelpers.py", line > 506, in oneshot > result = self.fget(obj, *args, **kw) > File ".../python2.7/site-packages/sqlalchemy/orm/properties.py", line > 156, in __clause_element__ > return self.adapter(self.prop.columns[0]) > File ".../python2.7/site-packages/sqlalchemy/orm/util.py", line 334, in > __adapt_element > return self.__adapter.traverse(elem).\ > File ".../python2.7/site-packages/sqlalchemy/sql/visitors.py", line 185, > in traverse > return replacement_traverse(obj, self.__traverse_options__, replace) > File ".../python2.7/site-packages/sqlalchemy/sql/visitors.py", line 281, > in replacement_traverse > obj = clone(obj, **opts) > File ".../python2.7/site-packages/sqlalchemy/sql/visitors.py", line 270, > in clone > newelem = replace(elem) > File ".../python2.7/site-packages/sqlalchemy/sql/visitors.py", line 182, > in replace > e = v.replace(elem) > File ".../python2.7/site-packages/sqlalchemy/sql/util.py", line 720, in > replace > return self._corresponding_column(col, True) > File ".../python2.7/site-packages/sqlalchemy/sql/util.py", line 695, in > _corresponding_column > require_embedded=require_embedded) > File ".../python2.7/site-packages/sqlalchemy/sql/expression.py", line > 2492, in corresponding_column > if self.c.contains_column(column): > File ".../python2.7/site-packages/sqlalchemy/util/langhelpers.py", line > 485, in __get__ > obj.__dict__[self.__name__] = result = self.fget(obj) > File ".../python2.7/site-packages/sqlalchemy/sql/expression.py", line > 2558, in columns > self._populate_column_collection() > File ".../python2.7/site-packages/sqlalchemy/sql/expression.py", line > 3704, in _populate_column_collection > col._make_proxy(self) > File ".../python2.7/site-packages/sqlalchemy/schema.py", line 1103, in > _make_proxy > fk = [ForeignKey(f.column) for f in self.foreign_keys] > File ".../python2.7/site-packages/sqlalchemy/util/langhelpers.py", line > 485, in __get__ > obj.__dict__[self.__name__] = result = self.fget(obj) > File ".../python2.7/site-packages/sqlalchemy/schema.py", line 1392, in > column > tname) > sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column > 'foo.bar_id' could not find table 'bar' with which to generate a foreign > key to target column 'id' > > > It looks like the problem is that mapper state is not being initialized > properly prior to setting up the column_property in the first two options. > Is there another type of property similar to declared_attr that will allow > me to add the column_property some place in the initialization sequence > where mappers have been sufficiently initialized to allow constructing a > select statement? > > ~ Daniel > > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. 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