擅长:python、mysql、java
<p>我认为最简单的方法是这样:</p>
<pre><code># brand is an instance of Brand
if not brand.cars_set.all():
# delete
else:
# do something else
</code></pre>
<p><a href="https://docs.djangoproject.com/en/dev/topics/db/examples/many_to_one/" rel="nofollow">Django docs</a>在相当多的细节中包含外键。</p>