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Fix #18062: Document best practices for choices in model fields.

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James Bennett 2012-08-08 12:49:28 -04:00
parent db729266d6
commit 7731cc8689
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47
docs/ref/models/fields.txt
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@ -86,42 +86,43 @@ field.
If this is given, Django's admin will use a select box instead of the standard If this is given, Django's admin will use a select box instead of the standard
text field and will limit choices to the choices given. text field and will limit choices to the choices given.
A choices list looks like this:: A choices list is an iterable of 2-tuples; the first element in each
tuple is the actual value to be stored, and the second element is the
human-readable name. For example::
YEAR_IN_SCHOOL_CHOICES = ( YEAR_IN_SCHOOL_CHOICES = (
('FR', 'Freshman'), ('FR', 'Freshman'),
('SO', 'Sophomore'), ('SO', 'Sophomore'),
('JR', 'Junior'), ('JR', 'Junior'),
('SR', 'Senior'), ('SR', 'Senior'),
('GR', 'Graduate'),
) )
The first element in each tuple is the actual value to be stored. The second Generally, it's best to define choices inside a model class, and to
element is the human-readable name for the option. define a suitably-named constant for each value::
The choices list can be defined either as part of your model class:: class Student(models.Model):
FRESHMAN = 'FR'
class Foo(models.Model): SOPHOMORE = 'SO'
JUNIOR = 'JR'
SENIOR = 'SR'
YEAR_IN_SCHOOL_CHOICES = ( YEAR_IN_SCHOOL_CHOICES = (
('FR', 'Freshman'), (FRESHMAN, 'Freshman'),
('SO', 'Sophomore'), (SOPHOMORE, 'Sophomore'),
('JR', 'Junior'), (JUNIOR, 'Junior'),
('SR', 'Senior'), (SENIOR, 'Senior'),
('GR', 'Graduate'),
) )
year_in_school = models.CharField(max_length=2, choices=YEAR_IN_SCHOOL_CHOICES) year_in_school = models.CharField(max_length=2,
choices=YEAR_IN_SCHOOL_CHOICES,
default=FRESHMAN)
or outside your model class altogether:: def is_upperclass(self):
return self.year_in_school in (self.JUNIOR, self.SENIOR)
YEAR_IN_SCHOOL_CHOICES = ( Though you can define a choices list outside of a model class and then
('FR', 'Freshman'), refer to it, defining the choices and names for each choice inside the
('SO', 'Sophomore'), model class keeps all of that information with the class that uses it,
('JR', 'Junior'), and makes the choices easy to reference (e.g, ``Student.SOPHOMORE``
('SR', 'Senior'), will work anywhere that the ``Student`` model has been imported).
('GR', 'Graduate'),
)
class Foo(models.Model):
year_in_school = models.CharField(max_length=2, choices=YEAR_IN_SCHOOL_CHOICES)
You can also collect your available choices into named groups that can You can also collect your available choices into named groups that can
be used for organizational purposes:: be used for organizational purposes::