Re: Weird date math bug?

A few tips on your code:

def get_latest_chemo(self):
chemo = ChemoRegime.objects.filter(patient=self).latest('stop_date')

class ChemoRegime(models.Model):
patient = models.ForeignKey(Patient, on_delete=models.CASCADE)

Use the related manager here. To make it readable, use:

class ChemoRegime(models.Model):
patient = models.ForeignKey(Patient, on_delete=models.CASCADE,
related_name='chemo_regimes')

class Patient(models.Model):
def get_latest_chemo(self):
return self.chemo_regimes.latest('stop_date')

When providing properties for use in templates, make them properties -
makes the template more readable:

@property
def latest_chemo(self):
return self.chemo_regimes.latest('stop_date')

{{ patient.latest_chemo }}

Similarly you can abstract active regimes:

class ChemoRegime(models.Model):
@property
def is_active(self):
return self.stop_date is None

{% if chemo.is_active %}<span class="badge
badge-primary">Current</span>{% endif %}


Of course, latest_chemo, should really be this if
active and non-active regimes can be mixed:

@property
def has_active_chemo(self):
return self.chemo_regimes.filter(stop_date__isnull=True).count() > 0

@property
def latest_chemo(self):
if not self.chemo_regimes.count():
return None
if self.has_active_chemo:
return self.chemo_regimes.latest('start_date')
return self.chemo_regimes.latest('stop_date')

Hope this helps :)

On Fri, Sep 1, 2017 at 7:22 AM, Lachlan Musicman <datakid@gmail.com> wrote:
> On 1 September 2017 at 14:57, James Schneider <jrschneider83@gmail.com>
> wrote:
>>
>> I'm guessing that ChemoRegime.regime_age() contains line 95.
>>
>> ChemoRegime defines the stop_date field with null=True and blank=True. I'm
>> guessing this is because patients may not have yet stopped treatment, so
>> they have no stop_date.
>>
>> With that in mind, self.stop_date may be None in Python (and Null in the
>> DB). Subtracting None from a real datetime.date object is not supported.
>>
>> Ensure that stop_date has a date value before doing date math with it.
>>
>> -James
>>
>
> I am so embarrassed. Thank you James, spot on.
>
> cheers
> L.
>
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