check if model was recently updated fails trying to use timedelta-CodePudding

I have the following model that saves a datetime on save:

class StockInfo(models.Model):
    ticker = models.CharField(max_length=100)
    current_price = models.FloatField()
    name = models.CharField(max_length=255)
    summary = models.TextField()
    sector = models.CharField(max_length=100)
    dividends = models.ArrayField(model_container=Dividend)
    last_updated_time = models.DateTimeField(null=True)

    objects = models.DjongoManager()

    # https://stackoverflow.com/questions/9953427/django-custom-save-model
    def save(self, *args, **kwargs):
        self.last_updated_time = datetime.datetime.now().astimezone()
        super(StockInfo, self).save(*args, **kwargs)

In the view I try using a timedelta to determine if the model had been updated within the last minute:

the_timedelta = stock.last_updated_time.replace(tzinfo=None) - now
print(the_timedelta)
if the_timedelta > datetime.timedelta(minutes=1):
    print("stock was updated within the last minute")
else:
    print("stock hasn't been updated recently")

I was expecting it to determine these rapid updates were within a minute:

found the stock
the last updated time for stock good before save: 08/15/2022 07:51:09
-1 day, 23:59:31.335919
stock hasn't been updated recently
the last updated time for stock good after save: 08/15/2022 07:51:38

reversing the comparison to if the_timedelta < datetime.timedelta(minutes=1): causes the opposite error:

the last updated time for stock stag before save: 08/15/2022 07:51:37
-1 day, 23:50:47.073490
stock was updated within the last minute
the last updated time for stock stag after save: 08/15/2022 08:00:50

I would like to be able to determine if the stock object was saved in the last 60 seconds and if so I don't need to make another API request so soon

CodePudding user response：

The reason that the timedelta comparison isn't working as expected is the date difference calculation is the wrong way around, hence the -1 day result. It should be:

now - stock.last_updated_time.replace(tzinfo=None)

The now datetime should be greater than the last updated time and give an answer in just minutes/seconds that can be compared to timedelta.

CodePudding user response：

        the_timedelta = now - stock.last_updated_time.replace(tzinfo=None)
        print(the_timedelta)
        # https://stackoverflow.com/questions/12484003/what-is-the-best-way-to-check-if-time-is-within-a-certain-minute
        if the_timedelta < datetime.timedelta(minutes=5):
             print("stock was updated within the last 5 minutes...no need to make an api call")
             current_price = stock.current_price
        else:
            print("stock hasn't been updated recently, make api call")
            current_price = get_recent_price_or_database_saved_price(ticker=ticker, stock=stock)