mirror of
https://github.com/django/django.git
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7414704e88
Special thanks to Hannes Ljungberg for finding multiple implementation gaps. Thanks also to Simon Charette, Adam Johnson, and Mariusz Felisiak for reviews.
67 lines
2.0 KiB
Python
67 lines
2.0 KiB
Python
"""
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Callable defaults
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You can pass callable objects as the ``default`` parameter to a field. When
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the object is created without an explicit value passed in, Django will call
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the method to determine the default value.
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This example uses ``datetime.datetime.now`` as the default for the ``pub_date``
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field.
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"""
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from datetime import datetime
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from django.db import models
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from django.db.models.functions import Coalesce, ExtractYear, Now, Pi
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from django.db.models.lookups import GreaterThan
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class Article(models.Model):
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headline = models.CharField(max_length=100, default="Default headline")
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pub_date = models.DateTimeField(default=datetime.now)
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def __str__(self):
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return self.headline
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class DBArticle(models.Model):
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"""
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Values or expressions can be passed as the db_default parameter to a field.
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When the object is created without an explicit value passed in, the
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database will insert the default value automatically.
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"""
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headline = models.CharField(max_length=100, db_default="Default headline")
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pub_date = models.DateTimeField(db_default=Now())
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class Meta:
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required_db_features = {"supports_expression_defaults"}
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class DBDefaults(models.Model):
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both = models.IntegerField(default=1, db_default=2)
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null = models.FloatField(null=True, db_default=1.1)
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class DBDefaultsFunction(models.Model):
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number = models.FloatField(db_default=Pi())
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year = models.IntegerField(db_default=ExtractYear(Now()))
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added = models.FloatField(db_default=Pi() + 4.5)
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multiple_subfunctions = models.FloatField(db_default=Coalesce(4.5, Pi()))
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case_when = models.IntegerField(
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db_default=models.Case(models.When(GreaterThan(2, 1), then=3), default=4)
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)
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class Meta:
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required_db_features = {"supports_expression_defaults"}
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class DBDefaultsPK(models.Model):
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language_code = models.CharField(primary_key=True, max_length=2, db_default="en")
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class DBDefaultsFK(models.Model):
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language_code = models.ForeignKey(
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DBDefaultsPK, db_default="fr", on_delete=models.CASCADE
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)
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