__init__.py

page_tags = Table('page_tags', meta.metadata,
    Column('page_id', Integer, ForeignKey('pages.id'), primary_key=True),
    Column('tag_id', Integer, ForeignKey('tags.id'), primary_key=True)
)

class Metadata(AppBase, Base):
    __tablename__ = 'metadata'

    id      = Column(Integer, primary_key=True)
    page_id = Column(Integer, ForeignKey('pages.id'))
    name    = Column(String, nullable=False)
    value   = Column(String)

class Tag(AppBase, Base):
    __tablename__ = 'tags'

    id   = Column(Integer, primary_key=True)
    name = Column(String, nullable=False, unique=True)

class Page(AppBase, Base):
    __tablename__ = 'pages'

    id          = Column(Integer, primary_key=True)
    path        = Column(String, nullable=False, unique=True)
    parent      = Column(String)
    last_update = Column(DateTime)
    accesses    = Column(Integer, nullable=False, default=0)

    tags_list = relation('Tag', backref='pages', secondary=page_tags, cascade='all')
    tags      = association_proxy('tags_list', 'name')

    data_map  = relation('Metadata', backref='page', collection_class=column_mapped_collection(Metadata.name), cascade='all')
    data      = association_proxy('data_map', 'value')
    
    def update(self, data):
        removed = set(self.data.keys()) - set(data.keys())
        added   = set(data.keys()) - set(self.data.keys())

        for i in removed:
            del self.data[i]

        for i in added:
            self.data_map[i] = Metadata(name=i, value=data[i])

        print self.data

        if 'tags' in self.data:

            tag_names    = set(self.data['tags'].value.split())
            added_tags   = tag_names - set(self.tags)
            removed_tags = set(self.tags) - tag_names

            for i in added_tags:
                t = meta.Session.query(Tag).filter_by(name=i).first()
                if t is None:
                    t = Tag(name=i)
                self.tags_list.append(t)
                
            for i in removed_tags:
                self.tags.remove(i)

        self.last_update = datetime.now()