This code:
import datetime
d_tomorrow = datetime.date.today() + datetime.timedelta(days=1)
class Model(models.Model):
...
timeout = models.DateTimeField(null=True, blank=True, default=d_tomorrow)
...
resuls in this error:
'datetime.date' object has no attribute 'date'
What am I doing wrong?
d_tomorrow is expected, by the Django ORM, to have a date attribute (apparently), but doesn't.
At any rate, you probably want to use a callable for the default date; otherwise, every model's default date will be "tomorrow" relative to the time the model class was initialized, not the time that the model is created. You might try this:
import datetime
def tomorrow():
return datetime.date.today() + datetime.timedelta(days=1)
class Model(models.Model):
timeout = models.DateTimeField(null=True, blank=True, default=tomorrow)
Problem solved:
from datetime import datetime, time, date, timedelta
def tomorrow():
d = date.today() + timedelta(days=1)
t = time(0, 0)
return datetime.combine(d, t)
models.DateTimeField expects the value to be datetime.datetime, not datetime.date
2015 Update:
Arrow makes this all much more straight forward.
Arrow is a Python library that offers a sensible, human-friendly approach to creating, manipulating, formatting and converting dates, times, and timestamps. It implements and updates the datetime type, plugging gaps in functionality, and provides an intelligent module API that supports many common creation scenarios. Simply put, it helps you work with dates and times with fewer imports and a lot less code.
Arrow is heavily inspired by moment.js and requests.
I had this problem when using the model from django.contrib.admin. I had two similar models, both with a date field (and both using auto_now_date=True - complete red herring); one worked, one had this error.
Turned out to be
def __unicode__(self):
return self.date
goes BANG, while this
def __unicode__(self):
return u'%s' % self.date
works just fine. Which is kind of obvious after the event, as usual.
This works for me:
import datetime
from datetime import timedelta
tomorrow = datetime.date.today() + timedelta(days=1)
class Test(models.Model):
timeout = models.DateTimeField(db_index=True, default=tomorrow)
Alternatively you could use tomorrow = datetime.datetime.now() + timedelta(days=1)
I tried out your code and it worked just fine. Can you verify that you are not modifying/redefining the import in some way?
Also try this:
import datetime as DT
d_tomorrow = DT.date.today() + DT.timedelta(days=1)
class Model(models.Model):
timeout = models.DateTimeField(null=True, blank=True, default=d_tomorrow)
Related
I have an Order model like so:
class Order(models.Model):
created_at = models.DateTimeField(...)
An order can be created at any time, but all orders get shipped out on the following Monday.
How can I add an extra field to my orders queryset called assembly_date that reflects the next Monday (date the order should be shipped)?
I tried creating a custom OrderManager like so, but am not sure how to correctly set the assembly_date:
from django.db.models import F, ExpressionWrapper, DateField
from django.db.models.functions import ExtractWeekDay
class OrderManager(models.Manager):
def get_queryset():
# need help with logic here:
return self.super().get_queryset().annotate(
assembly_date = ExpressionWrapper(
F("created_at") - ExtractWeekDay("created_at"),
output_field = DateField(),
)
)
But this operation results in the following error:
django.db.utils.ProgrammingError: operator does not exist: timestamp with time zone - double precision
LINE 1: ...E NULL END) * 2628000.0) * INTERVAL '1 seconds')) - EXTRACT(...
^
HINT: No operator matches the given name and argument types. You might need to add explicit type casts.
Keep in mind, I want to be able to filter all orders based on their assembly_date.
Basically you need to dynamically generate timedelta inside of annotate. But as far as I know, there is no way you can apply isoweekday() to a datetimefield inside of annotate.
You can have another field as assembly_date in your model, and use it directly to query.
from datetime import timedelta, date
class Order(models.Model):
created_at = models.DateTimeField(...)
assembly_date = models.DateTimeField(...)
def save(self, *args, **kwargs):
weekday = self.created_at.isoweekday() # 1 is Monday, 2 is Tuesday.
daysdiff = 8 - weekday
self.assembly_date = self.created_at + timedelta(days= daysdiff)
super(Order, self).save(*args, **kwargs)
I want an "active_in" attribute as a timeframe. I assume that the DBMS is optimized for the postgresql tsrange field, and as such it is preferable to utilize the DateTimeRangeField rather than 2 separate fields for start_date and end_date.
Doing this I desire a default value for the field.
active_in = models.DateTimeRangeField(default=timezone.now+'-'+timezone.now+10YEARS)
Is my assumption about the DateTimeRangeField performance true?
Is there a smart solution be it creating a new; function,class or
simply manipulating the 2nd last digit?
My possible solutions:
Code using string manipulation:
active_in = models.DateTimeRangeField(default=timezone.now+'-'+timezone.now[:-2]+'30')
Code using custom function object: (adjusted from here: https://stackoverflow.com/a/27491426/7458018)
def today_years_ahead():
return timezone.now + '-' timezone.now() + timezone.timedelta(years=10)
class MyModel(models.Model):
...
active_in = models.DateTimeRangeField(default=today_years_ahead)
There's no need for string manipulation, as the documented Python type for this field is DateTimeTZRange.
I can't say I've ever used this field before, but something like this should work:
from psycopg2.extras import DateTimeTZRange
from django.utils import timezone
from datetime import timedelta
def next_ten_years():
now = timezone.now()
# use a more accurate version of "10 years" if you need it
return DateTimeTZRange(now, now + timedelta(days=3652))
class MyModel(models.Model):
...
active_in = models.DateTimeRangeField(default=next_ten_years)
Python3.6.4; Django 2.0. Long time first time, please be gentle
I'm creating a tracking application that accepts multiple work logs to a work order. I'm trying to track time spent on a workorder by obtaining a time delta from each log and sending it to the work order model to hold the aggregate time.
The problem is, each time I'm updating an existing log it adds the entire time to the work order instead of just the difference. So if a log was previously 12-2:00 (feeds 2 hours to WorkOrder), and you changed it to 12-1:30 it was feed an additional 1.5 hours to WorkOrder, instead of subtracting 30min
Is there a way I can check to see a time was previously sent to WorkOrder? I tried updating update_labor_hours to check if the timedelta was < or > the original time, but I couldn't really figure it out.
Any help is appreciated!
from django.utils.timezone import now
from datetime import datetime, date, timedelta
from django.db import models
from django.db.models.signals import post_save
# Create your models here.
class WorkOrder(models.Model):
labor_hours = models.DurationField(blank=True, null=True)
class WorkLog(models.Model):
work_order = models.ForeignKey(WorkOrder, on_delete=models.PROTECT)
start_time = models.TimeField(blank=True, null=True)
end_time = models.TimeField(blank=True, null=True)
def _time_spent(self):
return datetime.combine(date.today(), self.end_time) - datetime.combine(date.today(), self.start_time)
time_spent = property(_time_spent)
def update_labor_hours(sender, instance, *args, **kwargs):
instance.work_order.labor_hours = instance.work_order.labor_hours + instance.time_spent
instance.work_order.save()
post_save.connect(update_labor_hours, sender=WorkLog)
In a Django app, I keep daily scores of users in such a model:
class Score(models.Model):
user = models.ForeignKey(User)
score = models.PositiveIntegerField(default=0)
date = models.DateField(auto_now_add=True)
I want to find out the days when a user's score has changed drastically compared to a consequent day. That is, if for example, the user scores 10 times higher than the previous day.
How can I include such a condition in a query filter using Django ORM? Is it possible with a single query using conditional expressions as described here: https://docs.djangoproject.com/en/1.9/ref/models/conditional-expressions/
Thanks.
If you change your Score class slightly to include the previous day's score (which is admittedly pretty wasteful), you can pack the query into one line using F expressions.
Your new class:
class Score(models.Model):
user = models.ForeignKey(User)
score = models.PositiveIntegerField(default=0)
lastscore = models.PositiveIntegerField(default=0)
date = models.DateField(auto_now_add=True)
Then the filter becomes:
from django.db.models import F
daily_chg = 10
big_changes = Score.objects.filter(score__gt=daily_chg*F('lastscore'))
Instead of using timedeltas to search for and set the previous day's score field, I'd look into establishing an ordering via a Meta class and calling latest() when saving the current day's score.
Using timedelta we can test for the last week's days for a given user as such:
from my_app.models import Score
import datetime
def some_view(request):
days_with_score_boost = []
today = datetime.date.today()
for each_day in xrange(0,7):
day_to_test, day_before_to_test = today - datetime.timedelta(days=each_day), today - datetime.timedelta(days=each_day + 1)
day_before_score = Score.objects.get(user=request.user,date=today - datetime.timedelta(days=each_day)).score # will need to catch the exception raised if .get return None and process appropriately
if Score.objects.filter(user=request.user,score__gte=days_before_score * 10,date=day_before_to_test).count() > 0:
days_with_score_boost.append(day_to_test)
days_with_score_boost will be a list of datetime.date objects where the score increased by 10 or more from the day before.
In reponse to your comment, I'd make a measure that checks at save time whether the score boost has occured. However, I would get rid of auto_now_add in favor of writing in the save method.
from django.utils import timezone
from django.core.exceptions import ObjectDoesNotExist
class Score(models.Model):
user = models.ForeignKey(User)
score = models.PositiveIntegerField(default=0)
date = models.DateField(null=True,blank=True)
increased_ten_over_previous_day = models.BooleanField(null=True,blank=True)
def save(self, *args, **kwargs):
self.date = timezone.now().today()
try:
yesterday_score = Score.objects.get(date=self.date-timezone.timedelta(days=1)).score
self.increased_ten_over_previous_day = (yesterday_score * 10) <= self.score
except ObjectDoesNotExist: # called if Score.object.get returns no object; requires you only have one score per user per date
self.increased_ten_over_previous_day = False
super(self, Score).save(*args, **kwargs)
Then you could filter objects for a date_range where increased_ten_over_previous_day is True.
EDITED:
How can I set a Django field's default to a function that gets evaluated each time a new model object gets created?
I want to do something like the following, except that in this code, the code gets evaluated once and sets the default to the same date for each model object created, rather than evaluating the code each time a model object gets created:
from datetime import datetime, timedelta
class MyModel(models.Model):
# default to 1 day from now
my_date = models.DateTimeField(default=datetime.now() + timedelta(days=1))
ORIGINAL:
I want to create a default value for a function parameter such that it is dynamic and gets called and set each time the function is called. How can I do that? e.g.,
from datetime import datetime
def mydate(date=datetime.now()):
print date
mydate()
mydate() # prints the same thing as the previous call; but I want it to be a newer value
Specifically, I want to do it in Django, e.g.,
from datetime import datetime, timedelta
class MyModel(models.Model):
# default to 1 day from now
my_date = models.DateTimeField(default=datetime.now() + timedelta(days=1))
The question is misguided. When creating a model field in Django, you are not defining a function, so function default values are irrelevant:
from datetime import datetime, timedelta
class MyModel(models.Model):
# default to 1 day from now
my_date = models.DateTimeField(default=datetime.now() + timedelta(days=1))
This last line is not defining a function; it is invoking a function to create a field in the class.
In this case datetime.now() + timedelta(days=1) will be evaluated once, and stored as the default value.
PRE Django 1.7
Django [lets you pass a callable as the default][1], and it will invoke it each time, just as you want:
from datetime import datetime, timedelta
class MyModel(models.Model):
# default to 1 day from now
my_date = models.DateTimeField(default=lambda: datetime.now() + timedelta(days=1))
Django 1.7+
Please note that since Django 1.7, usage of lambda as default value is not recommended (c.f. #stvnw comment). The proper way to do this is to declare a function before the field and use it as a callable in default_value named arg:
from datetime import datetime, timedelta
# default to 1 day from now
def get_default_my_date():
return datetime.now() + timedelta(days=1)
class MyModel(models.Model):
my_date = models.DateTimeField(default=get_default_my_date)
More information in the #simanas answer below
[1]: https://docs.djangoproject.com/en/dev/ref/models/fields/#default
Doing this default=datetime.now()+timedelta(days=1) is absolutely wrong!
It gets evaluated when you start your instance of django. If you are under apache it will probably work, because on some configurations apache revokes your django application on every request, but still you can find you self some day looking through out your code and trying to figure out why this get calculated not as you expect.
The right way of doing this is to pass a callable object to default argument. It can be a datetime.today function or your custom function. Then it gets evaluated every time you request a new default value.
def get_deadline():
return datetime.today() + timedelta(days=20)
class Bill(models.Model):
name = models.CharField(max_length=50)
customer = models.ForeignKey(User, related_name='bills')
date = models.DateField(default=datetime.today)
deadline = models.DateField(default=get_deadline)
There's an important distinction between the following two DateTimeField constructors:
my_date = models.DateTimeField(auto_now=True)
my_date = models.DateTimeField(auto_now_add=True)
If you use auto_now_add=True in the constructor, the datetime referenced by my_date is "immutable" (only set once when the row is inserted to the table).
With auto_now=True, however, the datetime value will be updated every time the object is saved.
This was definitely a gotcha for me at one point. For reference, the docs are here:
https://docs.djangoproject.com/en/dev/ref/models/fields/#datetimefield
Sometimes you may need to access model data after creating a new user model.
Here is how I generate a token for each new user profile using the first 4 characters of their username:
from django.dispatch import receiver
class Profile(models.Model):
auth_token = models.CharField(max_length=13, default=None, null=True, blank=True)
#receiver(post_save, sender=User) # this is called after a User model is saved.
def create_user_profile(sender, instance, created, **kwargs):
if created: # only run the following if the profile is new
new_profile = Profile.objects.create(user=instance)
new_profile.create_auth_token()
new_profile.save()
def create_auth_token(self):
import random, string
auth = self.user.username[:4] # get first 4 characters in user name
self.auth_token = auth + ''.join(random.SystemRandom().choice(string.ascii_uppercase + string.digits + string.ascii_lowercase) for _ in range(random.randint(3, 5)))
You can't do that directly; the default value is evaluated when the function definition is evaluated. But there are two ways around it.
First, you can create (and then call) a new function each time.
Or, more simply, just use a special value to mark the default. For example:
from datetime import datetime
def mydate(date=None):
if date is None:
date = datetime.now()
print date
If None is a perfectly reasonable parameter value, and there's no other reasonable value you could use in its place, you can just create a new value that's definitely outside the domain of your function:
from datetime import datetime
class _MyDateDummyDefault(object):
pass
def mydate(date=_MyDateDummyDefault):
if date is _MyDateDummyDefault:
date = datetime.now()
print date
del _MyDateDummyDefault
In some rare cases, you're writing meta-code that really does need to be able to take absolutely anything, even, say, mydate.func_defaults[0]. In that case, you have to do something like this:
def mydate(*args, **kw):
if 'date' in kw:
date = kw['date']
elif len(args):
date = args[0]
else:
date = datetime.now()
print date
Pass the function in as a parameter instead of passing in the result of the function call.
That is, instead of this:
def myfunc(date=datetime.now()):
print date
Try this:
def myfunc(date=datetime.now):
print date()