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"""
Specifying ordering
Specify default ordering for a model using the ``ordering`` attribute, which
should be a list or tuple of field names. This tells Django how to order
``QuerySet`` results.
If a field name in ``ordering`` starts with a hyphen, that field will be
ordered in descending order. Otherwise, it'll be ordered in ascending order.
The special-case field name ``"?"`` specifies random order.
The ordering attribute is not required. If you leave it off, ordering will be
undefined -- not random, just undefined.
"""
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=63, null=True, blank=True)
editor = models.ForeignKey("self", models.CASCADE, null=True)
class Meta:
ordering = ("-pk",)
class Article(models.Model):
author = models.ForeignKey(Author, models.SET_NULL, null=True)
second_author = models.ForeignKey(
Author, models.SET_NULL, null=True, related_name="+"
)
headline = models.CharField(max_length=100)
pub_date = models.DateTimeField()
class Meta:
ordering = (
"-pub_date",
models.F("headline"),
models.F("author__name").asc(),
models.OrderBy(models.F("second_author__name")),
)
class OrderedByAuthorArticle(Article):
class Meta:
proxy = True
ordering = ("author", "second_author")
class OrderedByFArticle(Article):
class Meta:
proxy = True
ordering = (models.F("author").asc(nulls_first=True), "id")
class ChildArticle(Article):
pass
class Reference(models.Model):
article = models.ForeignKey(OrderedByAuthorArticle, models.CASCADE)
proof = models.OneToOneField(Article, models.CASCADE, related_name="+")
class Meta:
ordering = ("article",)
class OrderedByExpression(models.Model):
name = models.CharField(max_length=30)
class Meta:
ordering = [models.functions.Lower("name")]
class OrderedByExpressionChild(models.Model):
parent = models.ForeignKey(OrderedByExpression, models.CASCADE)
class Meta:
ordering = ["parent"]
class OrderedByExpressionGrandChild(models.Model):
parent = models.ForeignKey(OrderedByExpressionChild, models.CASCADE)
class BarcodedArticle(models.Model):
rank = models.IntegerField(unique=True, null=True)
headline = models.CharField(max_length=100)
slug = models.CharField(max_length=100, default="slug")
pub_date = models.DateField(null=True)
barcode = models.CharField(max_length=30, default="bar")
class Meta:
required_db_features = {"supports_partial_indexes"}
unique_together = (("headline", "slug"),)
constraints = [
models.UniqueConstraint(
fields=["pub_date", "rank"],
name="unique_pub_date_rank",
),
models.UniqueConstraint(
fields=["rank"],
condition=models.Q(rank__gt=0),
name="unique_rank_conditional",
),
models.UniqueConstraint(
fields=["barcode"],
condition=models.Q(),
name="unique_barcode_empty_condition",
),
]
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