擅长:python、mysql、java
<p>如果要在<code>date_paid</code>为<code>None</code>时不应用检查:</p>
<pre><code>for instance in GratuityPayment.objects.all():
if instance.date_paid is not None and employment_number == instance.employment_number:
raise forms.ValidationError('This Employment Mumber was paid on ' + str(instance.date_paid) + '. You cannot proceed with this retirement')
</code></pre>
<p>但是,为什么不首先使用<a href="https://docs.djangoproject.com/en/1.9/topics/db/queries/#retrieving-specific-objects-with-filters" rel="nofollow">^{<cd3>}</a>只获取相关记录:</p>
<pre><code>GratuityPayment.objects.filter(date_paid__isnull=False,
employment_number=employment_number)
</code></pre>