blocks|key|2847341|text|您可以编写一个自定义save方法来检查YourObject.objects.all()的长度，然后在该长度等于10时删除最老的一个。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2847342|沿着…线的东西：|2847343|def+save(self,+*args,+**kwargs):
++++if+YourModel.objects.count()+==+10:
++++++++objects[0].delete()

++++super(YourModel,+self).save(*args,+**kwargs)|code-block|syntax|javascript|2847344|entityMap^0|A|4|J|O|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

You could write a custom <code>save</code> method that checks the length of <code>YourObject.objects.all()</code>, and then deletes the oldest one when that length is equal to 10. 

Something along the line of:

<pre><code>def save(self, *args, **kwargs):
 if YourModel.objects.count() == 10:
 objects[0].delete()

 super(YourModel, self).save(*args, **kwargs)
</code></pre>

blocks|key|1525563|text|在我看来，您可以使用信号。在这种情况下是post_save。这样，就可以将对象创建和删除逻辑分开。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1525564|由于您希望删除oldest，所以假设您在模型中有一个created字段。|1525565|一旦你save，|1525566|def+my_handler(sender,+instance,+**kwargs):
++++qs+=+MyModel.objects.order_by('created')+#ensure+ordering.
++++if+qs.count()+>+10:
++++++++qs[0].delete()+#remove+the+oldest+element

class+MyModel(models.Model):
++++title+=+models.CharField('title',+max_length=200)
++++created+=+models.DateTimeField(auto_add_now=True,+editable=False)

post_save.connect(my_handler,+sender=MyModel)|code-block|syntax|javascript|1525567|当然，没有什么可以阻止您使用pre_save信号，但是只有当您绝对确信save方法不会失败时才使用它。|1525568|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.djangoproject.com/en/dev/topics/signals/#module-django.dispatch|1|https://docs.djangoproject.com/en/dev/ref/signals/#post-save|2|https://docs.djangoproject.com/en/dev/ref/signals/#django.db.models.signals.pre_save^0|K|9|A|2|0|K|9|1|0|7|6|Q|7|0|3|4|0|0|E|8|Z|4|E|8|2|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]|$9|18|A|19|1|1A]]|E|$]]|$1|F|3|G|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1J|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1K|8|@$9|1L|A|1M|B|C]|$9|1N|A|1O|B|C]]|D|@$9|1P|A|1Q|1|1R]]|E|$]]|$1|Q|3|-4|5|6|7|1S|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]|10|$5|T|U|V|E|$W|11]]]]

In my opinion, you can use <a href="https://docs.djangoproject.com/en/dev/topics/signals/#module-django.dispatch" rel="noreferrer">Signals</a>. A <a href="https://docs.djangoproject.com/en/dev/ref/signals/#post-save" rel="noreferrer"><code>post_save</code></a> in this case. This way, you keep the object creation and deletion logic separate.

Since you want the <code>oldest</code> to be deleted, I am assuming you have a <code>created</code> field in the model. 

Once you <code>save</code>,

<pre><code>def my_handler(sender, instance, **kwargs):
 qs = MyModel.objects.order_by('created') #ensure ordering.
 if qs.count() &gt; 10:
 qs[0].delete() #remove the oldest element

class MyModel(models.Model):
 title = models.CharField('title', max_length=200)
 created = models.DateTimeField(auto_add_now=True, editable=False)

post_save.connect(my_handler, sender=MyModel)
</code></pre>

Of course, nothing stops you from using the <a href="https://docs.djangoproject.com/en/dev/ref/signals/#django.db.models.signals.pre_save" rel="noreferrer"><code>pre_save</code></a> signal, but use it only if you are absolutely sure the <code>save</code> method wont fail.

blocks|key|2847400|text|改进一下@karthikr的答案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2847401|我还认为事后保存信号处理程序是最好的方法，但是在类方法中隔离函数并检查created标志。例如，如果您希望保存系统发送的最后1000封电子邮件的日志：|offset|length|style|CODE|2847402|from+django.db+import+models
from+django.db.models.signals+import+post_save

LOG_SIZE=1000

class+EmailLog(models.Model):
++++"""Keeps+a+log+of+the+1000+most+recent+sent+emails."""

++++sent_at+=+models.DateTimeField(auto_add_now=True)
++++message+=+models.TextField()
++++to_addr+=+models.EmailField()

++++@classmethod
++++def+post_create(
++++++++cls,
++++++++sender,
++++++++instance:+"EmailLog",
++++++++created:+bool,
++++++++*args,
++++++++**kwargs
++++):
++++++++if+created:+#+Indicates+if+it's+a+new+object
++++++++++++qset+=+EmailLog.objects.order_by("sent_at")+#+Force+ordering
++++++++++++if+qset.count()+>+LOG_SIZE:
++++++++++++++++qset[0].delete()


post_save.connect(EmailLog.post_create,+sender=EmailLog)|code-block|syntax|javascript|2847403|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.djangoproject.com/en/3.2/ref/signals/#post-save^0|0|Z|7|4|4|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@$D|W|E|X|F|G]]|9|@$D|Y|E|Z|1|10]]|A|$]]|$1|H|3|I|5|J|7|11|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

Improving a bit on @karthikr answer.
I also believe a <a href="https://docs.djangoproject.com/en/3.2/ref/signals/#post-save" rel="nofollow noreferrer">post-save</a> signal handler is the best way, but isolating the function in a class method and checking for the <code>created</code> flag. If for example you want to keep a log of the last 1000 emails your system has sent:
<pre><code>from django.db import models
from django.db.models.signals import post_save

LOG_SIZE=1000

class EmailLog(models.Model):
 &quot;&quot;&quot;Keeps a log of the 1000 most recent sent emails.&quot;&quot;&quot;

 sent_at = models.DateTimeField(auto_add_now=True)
 message = models.TextField()
 to_addr = models.EmailField()

 @classmethod
 def post_create(
 cls,
 sender,
 instance: &quot;EmailLog&quot;,
 created: bool,
 *args,
 **kwargs
 ):
 if created: # Indicates if it's a new object
 qset = EmailLog.objects.order_by(&quot;sent_at&quot;) # Force ordering
 if qset.count() &gt; LOG_SIZE:
 qset[0].delete()


post_save.connect(EmailLog.post_create, sender=EmailLog)
</code></pre>

I have a table in my models file and I want to design it such that there is a limit to ten rows in the table. When the limit is exceeded the oldest row will be deleted. For some context this is for a display on the front end that shows a user the ten most recent links they have accessed. I am new to Django so if anyone had a suggestion on how to do this, it would be greatly appreciated!

Limit the number of rows in a Django table

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我在我的模型文件中有一个表，我想设计它，使表中的行数限制为10行。超过限制时，将删除最老的行。对于某些上下文，这是用于前端显示，显示用户最近访问的10个链接。我对Django很陌生，所以如果有人对如何做这件事有建议的话，我会非常感激的！

问限制Django表中的行数
EN

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