Python – In Django, how does one filter a QuerySet with dynamic field lookups

djangodjango-modelspython

Given a class:

from django.db import models

class Person(models.Model):
    name = models.CharField(max_length=20)

Is it possible, and if so how, to have a QuerySet that filters based on dynamic arguments? For example:

 # Instead of:
 Person.objects.filter(name__startswith='B')
 # ... and:
 Person.objects.filter(name__endswith='B')

 # ... is there some way, given:
 filter_by = '{0}__{1}'.format('name', 'startswith')
 filter_value = 'B'

 # ... that you can run the equivalent of this?
 Person.objects.filter(filter_by=filter_value)
 # ... which will throw an exception, since `filter_by` is not
 # an attribute of `Person`.

Best Solution

Python's argument expansion may be used to solve this problem:

kwargs = {
    '{0}__{1}'.format('name', 'startswith'): 'A',
    '{0}__{1}'.format('name', 'endswith'): 'Z'
}

Person.objects.filter(**kwargs)

This is a very common and useful Python idiom.

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