103 lines
3.0 KiB
Python
103 lines
3.0 KiB
Python
"""
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Tests for defer() and only().
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"""
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from django.db import models
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from django.db.models.query_utils import DeferredAttribute
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class Secondary(models.Model):
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first = models.CharField(max_length=50)
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second = models.CharField(max_length=50)
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class Primary(models.Model):
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name = models.CharField(max_length=50)
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value = models.CharField(max_length=50)
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related = models.ForeignKey(Secondary)
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def __unicode__(self):
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return self.name
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def count_delayed_fields(obj, debug=False):
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"""
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Returns the number of delayed attributes on the given model instance.
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"""
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count = 0
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for field in obj._meta.fields:
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if isinstance(obj.__class__.__dict__.get(field.attname),
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DeferredAttribute):
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if debug:
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print field.name, field.attname
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count += 1
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return count
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__test__ = {"API_TEST": """
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To all outward appearances, instances with deferred fields look the same as
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normal instances when we examine attribut values. Therefore we test for the
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number of deferred fields on returned instances (by poking at the internals),
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as a way to observe what is going on.
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>>> s1 = Secondary.objects.create(first="x1", second="y1")
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>>> p1 = Primary.objects.create(name="p1", value="xx", related=s1)
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>>> qs = Primary.objects.all()
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>>> count_delayed_fields(qs.defer('name')[0])
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1
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>>> count_delayed_fields(qs.only('name')[0])
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2
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>>> count_delayed_fields(qs.defer('related__first')[0])
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0
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>>> obj = qs.select_related().only('related__first')[0]
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>>> count_delayed_fields(obj)
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2
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>>> obj.related_id == s1.pk
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True
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>>> count_delayed_fields(qs.defer('name').extra(select={'a': 1})[0])
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1
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>>> count_delayed_fields(qs.extra(select={'a': 1}).defer('name')[0])
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1
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>>> count_delayed_fields(qs.defer('name').defer('value')[0])
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2
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>>> count_delayed_fields(qs.only('name').only('value')[0])
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2
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>>> count_delayed_fields(qs.only('name').defer('value')[0])
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2
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>>> count_delayed_fields(qs.only('name', 'value').defer('value')[0])
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2
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>>> count_delayed_fields(qs.defer('name').only('value')[0])
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2
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>>> obj = qs.only()[0]
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>>> count_delayed_fields(qs.defer(None)[0])
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0
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>>> count_delayed_fields(qs.only('name').defer(None)[0])
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0
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User values() won't defer anything (you get the full list of dictionaries
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back), but it still works.
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>>> qs.defer('name').values()[0] == {'id': p1.id, 'name': u'p1', 'value': 'xx', 'related_id': s1.id}
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True
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>>> qs.only('name').values()[0] == {'id': p1.id, 'name': u'p1', 'value': 'xx', 'related_id': s1.id}
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True
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Using defer() and only() with get() is also valid.
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>>> count_delayed_fields(qs.defer('name').get(pk=p1.pk))
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1
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>>> count_delayed_fields(qs.only('name').get(pk=p1.pk))
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2
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# KNOWN NOT TO WORK: >>> count_delayed_fields(qs.only('name').select_related('related')[0])
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# KNOWN NOT TO WORK >>> count_delayed_fields(qs.defer('related').select_related('related')[0])
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# Saving models with deferred fields is possible (but inefficient, since every
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# field has to be retrieved first).
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>>> obj = Primary.objects.defer("value").get(name="p1")
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>>> obj.name = "a new name"
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>>> obj.save()
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>>> Primary.objects.all()
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[<Primary: a new name>]
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"""}
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