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120 lines
3.5 KiB
Python
120 lines
3.5 KiB
Python
from django.db import models
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from django.db.models.fields.related import ReverseManyToOneDescriptor
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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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class CustomForeignObjectRel(models.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().__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, 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_fields(self, reverse_join=False):
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return ()
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def get_path_info(self, filtered_relation=None):
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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 [
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PathInfo(
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from_opts=from_opts,
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to_opts=to_opts,
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target_fields=(to_opts.pk,),
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join_field=self,
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m2m=False,
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direct=False,
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filtered_relation=filtered_relation,
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)
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]
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def get_reverse_path_info(self, filtered_relation=None):
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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 [
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PathInfo(
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from_opts=from_opts,
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to_opts=to_opts,
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target_fields=(to_opts.pk,),
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join_field=self.remote_field,
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m2m=False,
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direct=False,
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filtered_relation=filtered_relation,
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)
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]
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def contribute_to_class(self, cls, name, private_only=False):
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super().contribute_to_class(cls, name, private_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, alias, related_alias):
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return None
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class SlugPage(models.Model):
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slug = models.CharField(max_length=20, unique=True)
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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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