I'm reading the tutorial here: https://docs.djangoproject.com/en/1.5/ref/models/fields/#choices and i'm trying to create a box where the user can select the month he was born in. What I tried was
MONTH_CHOICES = (
(JANUARY, "January"),
(FEBRUARY, "February"),
(MARCH, "March"),
....
(DECEMBER, "December"),
)
month = CharField(max_length=9,
choices=MONTHS_CHOICES,
default=JANUARY)
Is this correct? I see that in the tutorial I was reading, they for some reason created variables first, like so
FRESHMAN = 'FR'
SOPHOMORE = 'SO'
JUNIOR = 'JR'
SENIOR = 'SR'
Why did they create those variables? Also, the MONTHS_CHOICES is in a model called People, so would the code I provided create a "Months Choices) column in the database called called "People" and would it say what month the user was born in after he clicks on of the months and submits the form?
This question is related to
python
django
django-models
I would suggest to use django-model-utils instead of Django built-in solution. The main advantage of this solution is the lack of string declaration duplication. All choice items are declared exactly once. Also this is the easiest way for declaring choices using 3 values and storing database value different than usage in source code.
from django.utils.translation import ugettext_lazy as _
from model_utils import Choices
class MyModel(models.Model):
MONTH = Choices(
('JAN', _('January')),
('FEB', _('February')),
('MAR', _('March')),
)
# [..]
month = models.CharField(
max_length=3,
choices=MONTH,
default=MONTH.JAN,
)
And with usage IntegerField instead:
from django.utils.translation import ugettext_lazy as _
from model_utils import Choices
class MyModel(models.Model):
MONTH = Choices(
(1, 'JAN', _('January')),
(2, 'FEB', _('February')),
(3, 'MAR', _('March')),
)
# [..]
month = models.PositiveSmallIntegerField(
choices=MONTH,
default=MONTH.JAN,
)
You can't have bare words in the code, that's the reason why they created variables (your code will fail with NameError
).
The code you provided would create a database table named month
(plus whatever prefix django adds to that), because that's the name of the CharField
.
But there are better ways to create the particular choices you want. See a previous Stack Overflow question.
import calendar
tuple((m, m) for m in calendar.month_name[1:])
The cleanest solution is to use the django-model-utils
library:
from model_utils import Choices
class Article(models.Model):
STATUS = Choices('draft', 'published')
status = models.CharField(choices=STATUS, default=STATUS.draft, max_length=20)
https://django-model-utils.readthedocs.io/en/latest/utilities.html#choices
I think no one actually has answered to the first question:
Why did they create those variables?
Those variables aren't strictly necessary. It's true. You can perfectly do something like this:
MONTH_CHOICES = (
("JANUARY", "January"),
("FEBRUARY", "February"),
("MARCH", "March"),
# ....
("DECEMBER", "December"),
)
month = models.CharField(max_length=9,
choices=MONTH_CHOICES,
default="JANUARY")
Why using variables is better? Error prevention and logic separation.
JAN = "JANUARY"
FEB = "FEBRUARY"
MAR = "MAR"
# (...)
MONTH_CHOICES = (
(JAN, "January"),
(FEB, "February"),
(MAR, "March"),
# ....
(DEC, "December"),
)
Now, imagine you have a view where you create a new Model instance. Instead of doing this:
new_instance = MyModel(month='JANUARY')
You'll do this:
new_instance = MyModel(month=MyModel.JAN)
In the first option you are hardcoding the value. If there is a set of values you can input, you should limit those options when coding. Also, if you eventually need to change the code at the Model layer, now you don't need to make any change in the Views layer.
For those who are interested, I have created django-better-choices
library, that provides a nice interface to work with Django choices for Python 3.7+. It supports custom parameters, lots of useful features and is very IDE friendly.
You can define your choices as a class:
from django_better_choices import Choices
class PAGE_STATUS(Choices):
CREATED = 'Created'
PENDING = Choices.Value('Pending', help_text='This set status to pending')
ON_HOLD = Choices.Value('On Hold', value='custom_on_hold')
VALID = Choices.Subset('CREATED', 'ON_HOLD')
class INTERNAL_STATUS(Choices):
REVIEW = 'On Review'
@classmethod
def get_help_text(cls):
return tuple(
value.help_text
for value in cls.values()
if hasattr(value, 'help_text')
)
Then do the following operations and much much more:
print( PAGE_STATUS.CREATED ) # 'created'
print( PAGE_STATUS.ON_HOLD ) # 'custom_on_hold'
print( PAGE_STATUS.PENDING.display ) # 'Pending'
print( PAGE_STATUS.PENDING.help_text ) # 'This set status to pending'
'custom_on_hold' in PAGE_STATUS.VALID # True
PAGE_STATUS.CREATED in PAGE_STATUS.VALID # True
PAGE_STATUS.extract('CREATED', 'ON_HOLD') # ~= PAGE_STATUS.VALID
for value, display in PAGE_STATUS:
print( value, display )
PAGE_STATUS.get_help_text()
PAGE_STATUS.VALID.get_help_text()
And of course, it is fully supported by Django and Django Migrations:
class Page(models.Model):
status = models.CharField(choices=PAGE_STATUS, default=PAGE_STATUS.CREATED)
Full documentation here: https://pypi.org/project/django-better-choices/
For Django3.0+, use models.TextChoices
(see docs-v3.0 for enumeration types)
from django.db import models
class MyModel(models.Model):
class Month(models.TextChoices):
JAN = '1', "JANUARY"
FEB = '2', "FEBRUARY"
MAR = '3', "MAR"
# (...)
month = models.CharField(
max_length=2,
choices=Month.choices,
default=Month.JAN
)
Usage::
>>> obj = MyModel.objects.create(month='1')
>>> assert obj.month == obj.Month.JAN
>>> assert MyModel.Month(obj.month).label == 'JANUARY'
>>> assert MyModel.objects.filter(month=MyModel.Month.JAN).count() >= 1
>>> obj2 = MyModel(month=MyModel.Month.FEB)
>>> assert obj2.get_month_display() == obj2.Month(obj2.month).label
Source: Stackoverflow.com