Thanks for reply.
The reason is simple. I plan in the future to accommodate datetime range
into that column as well, so storing this logic as plain strings gives the
most flexibility. This is a project that I'm learning by making. So I would
like to try all the new features for later tasks.
I'm fascinated by hybrid_property, but is stuck now when trying to dispatch
functions at the SQL expression level.
Jinghui
On Fri, Sep 16, 2016 at 1:34 AM, Simon King <si...@simonking.org.uk> wrote:
> Ignore SQLAlchemy for the moment and describe what you are trying to
> achieve. It looks like you want to store dates and times as strings in
> your database (rather than the appropriate type), and yet still be
> able to perform date-related operations on them qhen querying. Is that
> right? Is there a reason why you can't store them as proper DateTime
> values (perhaps with a second column to indicate whether or not the
> time part is valid)?
>
> Simon
>
> On Fri, Sep 16, 2016 at 4:39 AM, Jinghui Niu <niujing...@gmail.com> wrote:
> > I have the following code snippet, I marked my question in a comment line
> > inside the hybrid_property.expression part. As you can see, it is now not
> > implemented:
> >
> > from sqlalchemy.ext.declarative import declared_attr
> > from sqlalchemy import Column, Integer, String, Unicode, UnicodeText
> > from sqlalchemy.ext.hybrid import hybrid_property, hybrid_method
> > import arrow
> >
> >
> > datetimeString_format = {
> > "UTC": "%Y-%m-%d %H:%M:%S+00:00",
> > "local_with_timezoneMarker": "%Y-%m-%d %H:%M:%S %Z",
> > "local_without_timezoneMarker": "%Y-%m-%d %H:%M:%S"
> > }
> >
> >
> > dateString_format = "%Y-%m-%d"
> >
> >
> > class My_TimePoint_Mixin:
> > # define output formats:
> > datetimeString_inUTC_format = "%Y-%m-%d %H:%M:%S+00:00"
> > datetimeString_naive_format = "%Y-%m-%d %H:%M:%S"
> >
> >
> > # instrumented fields:
> > _TimePoint_in_database = Column('timepoint', String, nullable=False)
> > _TimePoint_in_database_suffix = Column(
> > 'timepoint_suffix', String, nullable=False)
> >
> >
> > @hybrid_property
> > def timepoint(self):
> > twoPossibleType_handlers = [
> > self._report_ACCRT_DATE,
> > self._report_ACCRT_DATETIME
> > ]
> > for handler in twoPossibleType_handlers:
> > print("handler: ", handler)
> > try:
> > return handler(self)
> > except (AssertionError, ValueError) as e:
> > logging.warning("Try next handler!")
> >
> > @timepoint.expression
> > def timepoint(cls):
> > pass
> > # How can I implement SQL expression for a equivalent function
> > dispatch here? There seems to be no SQL equivalent structure for this?
> >
> >
> > @timepoint.setter
> > def timepoint(self, datetimepointOBJ):
> > handlers_lookup = {
> > datetime.datetime: self._set_ACCRT_DATETIME,
> > datetime.date: self._set_ACCRT_DATE
> > }
> > this_time = type(datetimepointOBJ)
> > this_handler = handlers_lookup[this_time]
> > print("handler: ", this_handler)
> > this_handler(datetimepointOBJ)
> >
> >
> > def _report_ACCRT_DATE(self):
> > """Accurate Date"""
> > assert self._TimePoint_in_database_suffix == "ACCRT_DATE"
> > date_string = self._TimePoint_in_database
> > dateString_format = "%Y-%m-%d"
> > # return a datetime.date
> > return datetime.datetime.strptime(date_string,
> > dateString_format).date()
> >
> >
> > def _report_ACCRT_DATETIME(self):
> > """Accurate DateTime"""
> > assert self._TimePoint_in_database_suffix in
> pytz.all_timezones_set
> > datetimeString_inUTC = self._TimePoint_in_database
> > utc_naive = datetime.datetime.strptime(
> > datetimeString_inUTC, self.datetimeString_inUTC_format)
> > utc_timepoint = arrow.get(utc_naive, "utc")
> > # localize
> > local_timepoint =
> > utc_timepoint.to(self._TimePoint_in_database_suffix)
> > # return a datetime.datetime
> > return local_timepoint.datetime
> >
> >
> > def _set_ACCRT_DATETIME(self, datetimeOBJ_aware):
> > assert isinstance(datetimeOBJ_aware, datetime.datetime), "Must
> be a
> > valid datetime.datetime!"
> > assert datetimeOBJ_aware.tzinfo is not None, "Must contain
> tzinfo!"
> > utctime_aware_arrow = arrow.get(datetimeOBJ_aware).to('utc')
> > utctime_aware_datetime = utctime_aware_arrow.datetime
> > store_datetime_string = utctime_aware_datetime.strftime(
> > self.datetimeString_inUTC_format)
> > self._TimePoint_in_database = store_datetime_string
> >
> >
> > def _set_ACCRT_DATE(self, dateOBJ):
> > store_date_string = dateOBJ.isoformat()
> > self._TimePoint_in_database = store_date_string
> >
> > Could someone please point out a clue as to implement the
> > hybrid_property.expression part? Thanks.
> >
> > I've also posted a similar issue on stackoverflow.com, for reference:
> >
> > http://stackoverflow.com/questions/39485440/calling-
> from-the-same-class-why-is-one-treated-as-bound-method-while-the-other
> >
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