How to use the ming.odm.base.state function in Ming

def __get__(self, instance, cls=None):
        if instance is None: return self
        st = state(instance)
        if not st.options.instrument:
            return st.document[self.name]
        try:
            return st.instrumented(self.name)
        except KeyError:
            value = self.field.schema.validate(S.Missing)
            if value is S.Missing:
                raise AttributeError(self.name)
            else:
                st.document[self.name] = value
            return value

def _next_impl(self):
        doc = next(self.ming_cursor)
        obj = self.session.imap.get(self.cls, doc['_id'])
        if obj is None:
            obj = self.mapper.create(doc, self._options, remake=False)
            state(obj).status = ObjectState.clean
            self.session.save(obj)
        elif self._options.refresh:
            # Refresh object
            state(obj).update(doc)
            state(obj).status = ObjectState.clean
        else:
            # Never refresh objects from the DB unless explicitly requested
            pass
        other_session = session(obj)
        if other_session is not None and other_session != self:
            other_session.expunge(obj)
            self.session.save(obj)
        if self._options.decorate is not None:
            return self._options.decorate(obj)
        else:
            return obj

If the session has ``autoflush`` option, the session
        if flushed before performing the query.

        It returns an :class:`.ODMCursor` with the results.
        """

        decorate = kwargs.pop('decorate', None)
        if self.autoflush:
            self.flush()
        m = mapper(cls)
        obj = self.impl.find_and_modify(m.collection, *args, **kwargs)
        if obj is None: return None
        cursor = ODMCursor(self, cls, iter([ obj ]), refresh=True, decorate=decorate)
        result = cursor.first()
        state(result).status = ObjectState.clean
        return result

def dirty(self):
        return (obj for obj in six.itervalues(self._objects)
                if state(obj).status == ObjectState.dirty)

def delete(self):
        """Mark the object for deletion on next flush"""
        st = state(self.instance)
        st.status = st.deleted

def expunge(self, obj):
        """Remove an object from the Session (and its UnitOfWork and IdentityMap)"""
        self.uow.expunge(obj)
        self.imap.expunge(obj)
        state(obj).session = None

def _next_impl(self):
        doc = next(self.ming_cursor)
        obj = self.session.imap.get(self.cls, doc['_id'])
        if obj is None:
            obj = self.mapper.create(doc, self._options, remake=False)
            state(obj).status = ObjectState.clean
            self.session.save(obj)
        elif self._options.refresh:
            # Refresh object
            state(obj).update(doc)
            state(obj).status = ObjectState.clean
        else:
            # Never refresh objects from the DB unless explicitly requested
            pass
        other_session = session(obj)
        if other_session is not None and other_session != self:
            other_session.expunge(obj)
            self.session.save(obj)
        if self._options.decorate is not None:
            return self._options.decorate(obj)
        else:
            return obj

def get_depot_history(cls, instance):
        istate = state(instance)
        if not hasattr(istate, '_depot_history'):
            istate._depot_history = _DepotHistory()
        return istate._depot_history

def _next_impl(self):
        doc = next(self.ming_cursor)
        obj = self.session.imap.get(self.cls, doc['_id'])
        if obj is None:
            obj = self.mapper.create(doc, self._options, remake=False)
            state(obj).status = ObjectState.clean
            self.session.save(obj)
        elif self._options.refresh:
            # Refresh object
            state(obj).update(doc)
            state(obj).status = ObjectState.clean
        else:
            # Never refresh objects from the DB unless explicitly requested
            pass
        other_session = session(obj)
        if other_session is not None and other_session != self:
            other_session.expunge(obj)
            self.session.save(obj)
        if self._options.decorate is not None:
            return self._options.decorate(obj)
        else:
            return obj

def clean(self):
        return (obj for obj in six.itervalues(self._objects)
                if state(obj).status == ObjectState.clean)