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46 lines
1.7 KiB
Python
46 lines
1.7 KiB
Python
from django.db.models import Manager
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from django.db.models.expressions import RawSQL
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NAT1 = r"CAST(SUBSTRING({}.{} FROM '^(\d{{1,9}})') AS integer)"
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NAT2 = r"SUBSTRING({}.{} FROM '^\d*(.*?)\d*$')"
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NAT3 = r"CAST(SUBSTRING({}.{} FROM '(\d{{1,9}})$') AS integer)"
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class NaturalOrderingManager(Manager):
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"""
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Order objects naturally by a designated field (defaults to 'name'). Leading and/or trailing digits of values within
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this field will be cast as independent integers and sorted accordingly. For example, "Foo2" will be ordered before
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"Foo10", even though the digit 1 is normally ordered before the digit 2.
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"""
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natural_order_field = 'name'
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def get_queryset(self):
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queryset = super().get_queryset()
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db_table = self.model._meta.db_table
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db_field = self.natural_order_field
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# Append the three subfields derived from the designated natural ordering field
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queryset = (
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queryset.annotate(_nat1=RawSQL(NAT1.format(db_table, db_field), ()))
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.annotate(_nat2=RawSQL(NAT2.format(db_table, db_field), ()))
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.annotate(_nat3=RawSQL(NAT3.format(db_table, db_field), ()))
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)
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# Replace any instance of the designated natural ordering field with its three subfields
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ordering = []
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for field in self.model._meta.ordering:
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if field == self.natural_order_field:
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ordering.append('_nat1')
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ordering.append('_nat2')
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ordering.append('_nat3')
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else:
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ordering.append(field)
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# Default to using the _nat indexes if Meta.ordering is empty
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if not ordering:
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ordering = ('_nat1', '_nat2', '_nat3')
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return queryset.order_by(*ordering)
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