Fields¶

Contains timezone-related fields.

TimeZoneField¶

class TimeZoneField(*args, **kwargs)¶

A models.CharField subclass that stores a valid Olson Timezone string found in pytz.all_timezones to the database.

Raises:	django.core.exceptions.ValidationError – if the value is not a valid Olson Time zone string.
Returns:	A `datetime.tzinfo` object based on the value or `None`.
Return type:	`datetime.tzinfo`

from timezone_utils.fields import TimeZoneField
from timezone_utils.choices import PRETTY_ALL_TIMEZONES_CHOICES

class Location(models.Model):
    # ...
    timezone = TimeZoneField(choices=PRETTY_ALL_TIMEZONES_CHOICES)

You can pass a default Olson timezone value to the model as a string:

from timezone_utils.fields import TimeZoneField

class Location(models.Model):
    # ...
    timezone = TimeZoneField(default='US/Pacific')

You can also pass a default Olson timezone value to the model as a pytz.timezone instance:

import pytz
from timezone_utils.fields import TimeZoneField

class Location(models.Model):
    # ...
    timezone = TimeZoneField(default=pytz.timezone('US/Eastern'))

Accessing a `TimeZoneField` on a model¶

As a convenience, TimeZoneField automatically converts its model instance attribute representation to a pytz.timezone instance:

>>> from datetime import datetime
>>> from django.utils.timezone import make_aware
>>> from app_label.models import Location
>>> location = Location.objects.create(timezone='US/Eastern')
>>> print(location.timezone)
<DstTzInfo 'US/Eastern' LMT-1 day, 19:04:00 STD>
>>> unaware_dt = datetime(2015, 1, 1)
>>> aware_dt = make_aware(unaware_dt, location.timezone)
>>> print(aware_dt)
datetime.datetime(2015, 1, 1, 0, 0, tzinfo=<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>)

LinkedTZDateTimeField¶

class LinkedTZDateTimeField(populate_from=None, time_override=None, *args, **kwargs)¶

A models.DateTimeField subclass that will automatically save a datetime object as a particular time zone as declared in the kwarg populate_from. You can also override the time each time the object is saved with the kwarg time_override, which must be a datetime.time instance.

Parameters:	populate_from – The location of the field which contains the time zone that will be used for this field. Must be either a function which returns a `models.ForeignKey` path to the timezone or a string (if the timezone field is located on the model). time_override – Automatically overrides the time value each time the object is saved to the time that is declared. Must be a `datetime.time` instance.
Raises:	AttributeError – if the `populate_from` parameter is invalid. ValueError – if the `time_override` is not a `datetime.time` instance. pytz.UnknownTimeZoneError – if the parsed model instance value of `populate_from` is not a valid Olson time zone string.
Returns:	A `datetime.datetime` object based on the time zone declared in `populate_from` and override from `time_override` or `None`.
Return type:	`datetime.datetime`

Note

If auto_now or auto_now_add is declared, the value of time_override is ignored.

Caution

Django cannot serialize lambdas! If you provide a lambda for populate_from, your model will fail to migrate in Django 1.7+.

from datetime import datetime
from timezone_utils.fields import LinkedTZDateTimeField, TimeZoneField
from timezone_utils.choices import PRETTY_ALL_TIMEZONES_CHOICES

class Location(models.Model):
    # ...
    timezone = TimeZoneField(choices=PRETTY_ALL_TIMEZONES_CHOICES)


def get_location_timezone(obj):
    return obj.location.timezone


class LocationReport(models.Model):
    # ...
    location = models.ForeignKey('app_label.Location', related_name='reports')
    timestamp = LinkedTZDateTimeField(populate_from=get_location_timezone)


class LocationPeriod(models.Model):
    # ...
    location = models.ForeignKey('app_label.Location', related_name='reports')
    start = LinkedTZDateTimeField(
        populate_from=get_location_timezone,
        time_override=datetime.min.time()
    )
    end = LinkedTZDateTimeField(
        populate_from=get_location_timezone,
        time_override=datetime.max.time()
    )

Accessing a `LinkedTZDateTimeField` on a model¶

As a convenience, LinkedTZDateTimeField automatically converts its model instance attribute representation to the time zone declared in the populate_from, regardless of what settings.TIME_ZONE is set to:

>>> from datetime import datetime
>>> from app_label.models import LocationPeriod
>>> location = location.objects.get(pk=1)
>>> location_period = LocationPeriod.objects.create(location=location, start=datetime(2015, 1, 1), end=datetime(2015, 12, 31))
>>> print(location_period.start)
datetime.datetime(2015, 1, 1, 0, 0, tzinfo=<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>)
>>> print(location_period.end)
datetime.datetime(2015, 12, 31, 23, 59, 59, 999999, tzinfo=<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>)

Accessing a `LinkedTZDateTimeField` in templates¶

Django templates will automatically cast the timezones to the currently-activated time zone for the user viewing the page. An example of how to display our fields with the appropriate time zone would look something like this:

app_label/views.py:

# Django
from django.views.generic import ListView

# App
from app_label.models import LocationPeriod


class LocationReportingPeriodListView(ListView):
    model = LocationPeriod
    template_name = 'app_label/location_period_list.html'

    def get_queryset(self):
        """Retrieve the queryset and perform select_related on `location` since
        we will be using it in the template.

        """
        return super(
            LocationReportingPeriodListView,
            self
        ).get_queryset().select_related(
            'location'
        )

templates/app_label/location_period_list.html:

{% load tz %}
{% load i18n %}

{% block content %}
    <table>
        <thead>
            <tr>
                <th>{% trans "Location" %}</th>
                <th>{% trans "Start" %}</th>
                <th>{% trans "End" %}</th>
            </tr>
        </thead>
        <tdata>
            {% for period in object_list %}
                {# Activate the timezone for each location #}
                {% timezone period.location.timezone %}
                    <tr>
                        <td>{{ period.location.name }}</td>
                        <td>{{ period.start }}</td>
                        <td>{{ period.end }}</td>
                    </tr>
                {% endtimezone %}
            {% empty %}
                <tr>
                    <td colspan=3>{% trans "No periods to display." %}</td>
                </tr>
            {% endfor %}
        </tdata>
    </table>
{% endblock content %}