On May 5, 2010, at 5:12 PM, Michael Bayer wrote: > > Since Python allows dynamic generation of classes, there are easy ways to > deal with this.
I forgot to mention a system that works almost like the recipe I gave is the SQLSoup extension, you might like it a lot: http://www.sqlalchemy.org/docs/reference/ext/sqlsoup.html > >> >> This presents a maintenance issue I would like to avoid. So I tried >> using 'meta.reflect(bind=engine)' which does indeed read all my tables >> in without the maintenance issues. However it creates generic Table() >> classes with no interface additions for the columns. This makes my >> queries basic SQL with some added sqlalchemy calls to get the table >> and dereference the columns. Also not desirable. > >> >> I believe this is due to the fact that Sqlalchemy chooses to modify >> the class definitions on reflection as opposed to class instances. > > I am assuming there is a breakdown of terminology occuring here. The > reflection process produces instances of the Table object with contained > Columns. These are not classes, they are instances. The classes in use are > sqlalchemy.schema.Table and sqlalchemy.schema.Column, and these do not change > nor are they dynamically extended. There is also no "dereferencing" step > I'm aware of unless you are referring to the present of the Column objects on > the .c. collection. The table metadata produced by the MetaData object has > no knowledge of the ORM or the declarative extension, but the ORM builds upon > these constructs. > > It sounds like you'd like a reflection process that produces > declarative-bound ORM classes, not Table instances. The recipe below > achieves this, by generating a new declarative class for each Table reflected > by the metadata. > > from sqlalchemy import * > from sqlalchemy.orm import * > from sqlalchemy.ext.declarative import declarative_base > > def declared_classes_for_tables(Base, engine): > result = {} > Base.metadata.reflect(engine) > for table in Base.metadata.tables.values(): > cls_ = type(str(table.name), (Base,), {'__table__':table}) > result[cls_.__name__] = cls_ > return result > > # demo > if __name__ == '__main__': > engine = create_engine('sqlite://', echo=True) > metadata = MetaData() > for name in ('peas', 'carrots', 'celery', 'brocolli'): > Table(name, metadata, > Column('id', Integer, primary_key=True), > Column('data', String(50)) > ) > metadata.create_all(engine) > > # now reflect the database into classes > Base = declarative_base() > classes = declared_classes_for_tables(Base, engine) > > sess = sessionmaker(engine)() > sess.add_all([ > classes['carrots'](data='carrot1'), > classes['peas'](data='pea1') > ]) > > print sess.query(classes['carrots']).all() > print sess.query(classes['peas']).all() > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalch...@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
