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e542e81b39
The old names were downright confusing. Some seemed to mean the opposite
of what the class actually did.
The new names follow a consistent nomenclature:
(Forward|Reverse)(ManyToOne|OneToOne|ManyToMany)Descriptor.
I mentioned combinations that do not exist in the docstring in order to
help people who would search for them in the code base.
101 lines
3.1 KiB
Python
101 lines
3.1 KiB
Python
from django.db import models
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from django.db.models.fields.related import (
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ForeignObjectRel, ReverseManyToOneDescriptor,
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)
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from django.db.models.lookups import StartsWith
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from django.db.models.query_utils import PathInfo
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from django.utils.encoding import python_2_unicode_compatible
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class CustomForeignObjectRel(ForeignObjectRel):
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"""
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Define some extra Field methods so this Rel acts more like a Field, which
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lets us use ReverseManyToOneDescriptor in both directions.
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"""
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@property
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def foreign_related_fields(self):
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return tuple(lhs_field for lhs_field, rhs_field in self.field.related_fields)
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def get_attname(self):
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return self.name
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class StartsWithRelation(models.ForeignObject):
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"""
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A ForeignObject that uses StartsWith operator in its joins instead of
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the default equality operator. This is logically a many-to-many relation
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and creates a ReverseManyToOneDescriptor in both directions.
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"""
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auto_created = False
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many_to_many = False
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many_to_one = True
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one_to_many = False
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one_to_one = False
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rel_class = CustomForeignObjectRel
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def __init__(self, *args, **kwargs):
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kwargs['on_delete'] = models.DO_NOTHING
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super(StartsWithRelation, self).__init__(*args, **kwargs)
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@property
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def field(self):
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"""
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Makes ReverseManyToOneDescriptor work in both directions.
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"""
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return self.remote_field
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def get_extra_restriction(self, where_class, alias, related_alias):
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to_field = self.remote_field.model._meta.get_field(self.to_fields[0])
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from_field = self.model._meta.get_field(self.from_fields[0])
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return StartsWith(to_field.get_col(alias), from_field.get_col(related_alias))
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def get_joining_columns(self, reverse_join=False):
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return tuple()
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def get_path_info(self):
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to_opts = self.remote_field.model._meta
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from_opts = self.model._meta
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return [PathInfo(from_opts, to_opts, (to_opts.pk,), self, False, False)]
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def get_reverse_path_info(self):
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to_opts = self.model._meta
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from_opts = self.remote_field.model._meta
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return [PathInfo(from_opts, to_opts, (to_opts.pk,), self.remote_field, False, False)]
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def contribute_to_class(self, cls, name, virtual_only=False):
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super(StartsWithRelation, self).contribute_to_class(cls, name, virtual_only)
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setattr(cls, self.name, ReverseManyToOneDescriptor(self))
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class BrokenContainsRelation(StartsWithRelation):
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"""
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This model is designed to yield no join conditions and
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raise an exception in ``Join.as_sql()``.
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"""
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def get_extra_restriction(self, where_class, alias, related_alias):
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return None
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@python_2_unicode_compatible
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class SlugPage(models.Model):
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slug = models.CharField(max_length=20)
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descendants = StartsWithRelation(
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'self',
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from_fields=['slug'],
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to_fields=['slug'],
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related_name='ascendants',
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)
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containers = BrokenContainsRelation(
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'self',
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from_fields=['slug'],
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to_fields=['slug'],
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)
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class Meta:
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ordering = ['slug']
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def __str__(self):
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return 'SlugPage %s' % self.slug
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