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"""
Callable defaults
You can pass callable objects as the ``default`` parameter to a field. When
the object is created without an explicit value passed in, Django will call
the method to determine the default value.
This example uses ``datetime.datetime.now`` as the default for the ``pub_date``
field.
"""
from datetime import datetime
from django.db import models
from django.db.models.functions import Coalesce, ExtractYear, Now, Pi
from django.db.models.lookups import GreaterThan
class Article(models.Model):
headline = models.CharField(max_length=100, default="Default headline")
pub_date = models.DateTimeField(default=datetime.now)
def __str__(self):
return self.headline
class DBArticle(models.Model):
"""
Values or expressions can be passed as the db_default parameter to a field.
When the object is created without an explicit value passed in, the
database will insert the default value automatically.
"""
headline = models.CharField(max_length=100, db_default="Default headline")
pub_date = models.DateTimeField(db_default=Now())
class Meta:
required_db_features = {"supports_expression_defaults"}
class DBDefaults(models.Model):
both = models.IntegerField(default=1, db_default=2)
null = models.FloatField(null=True, db_default=1.1)
class DBDefaultsFunction(models.Model):
number = models.FloatField(db_default=Pi())
year = models.IntegerField(db_default=ExtractYear(Now()))
added = models.FloatField(db_default=Pi() + 4.5)
multiple_subfunctions = models.FloatField(db_default=Coalesce(4.5, Pi()))
case_when = models.IntegerField(
db_default=models.Case(models.When(GreaterThan(2, 1), then=3), default=4)
)
class Meta:
required_db_features = {"supports_expression_defaults"}
class DBDefaultsPK(models.Model):
language_code = models.CharField(primary_key=True, max_length=2, db_default="en")
class DBDefaultsFK(models.Model):
language_code = models.ForeignKey(
DBDefaultsPK, db_default="fr", on_delete=models.CASCADE
)
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