blocks|key|547558|text|您不需要使用prefetch_related，因为这是用于many-to-many关系的，您可以使用select_related。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|547559|所以你的查询是|547560|pm2+=+Menu.objects.filter(
++++parent=None,+language__code=language,+menutype=menutype
).select_related(
++++"submenus"
).order_by(
++++"order"
)|code-block|syntax|javascript|547561|entityMap^0|6|G|T|C|1E|E|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]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

You don't need to use <code>prefetch_related</code> since this is used for <code>many-to-many</code> relationships, instead, you can use <code>select_related</code>.
So your query would be
<pre><code>pm2 = Menu.objects.filter(
 parent=None, language__code=language, menutype=menutype
).select_related(
 &quot;submenus&quot;
).order_by(
 &quot;order&quot;
)
</code></pre>

blocks|key|547582|text|因为您使用的是树(通过使用邻接列表)，所以如果您有多个父-子关系级别，那么select_related和prefetch_related都不能正常工作。相反，你将需要一些材料，使这棵树。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|547583|https://pypi.org/project/django-closure-tree/提供了一个构建Postgres视图的框架，它将处理这种类型的构造，并为您提供了一些使查询更简单的工具。|547584|这背后的实际代码非常简单：https://schinckel.net/2016/01/27/django-trees-via-closure-view/|547585|entityMap|0|LINK|mutability|MUTABLE|url|https://pypi.org/project/django-closure-tree/|1|https://schinckel.net/2016/01/27/django-trees-via-closure-view/^0|11|E|1G|G|0|0|19|0|0|D|1R|1|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|H|3|I|5|6|7|12|8|@]|D|@$9|13|A|14|1|15]]|E|$]]|$1|J|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]|R|$5|M|N|O|E|$P|S]]]]

Since you are working with a tree (by using an Adjacency List), then neither <code>select_related</code> nor <code>prefetch_related</code> will work correctly if you have more than a single level of parent-child relationships. Instead, you will need something that materialises the tree.

<a href="https://pypi.org/project/django-closure-tree/" rel="nofollow noreferrer">https://pypi.org/project/django-closure-tree/</a> provides a framework for building Postgres views that will handle this type of construct, and gives you some tools for making querying this simpler.

The actual code behind this is surprisingly simple: <a href="https://schinckel.net/2016/01/27/django-trees-via-closure-view/" rel="nofollow noreferrer">https://schinckel.net/2016/01/27/django-trees-via-closure-view/</a>

blocks|key|3463007|text|当我打印子菜单时，结果是app.Menu.None|type|blockquote|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3463008|之所以会发生这种情况，是因为OP正在打印print(p.submenus)，这只是一个RelatedManager。它可以通过检查p.submenus的类型来验证。|unstyled|3463009|#+this+is+what+it+prints+in+django+1.11
>>>+type(p.submenus)+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
django.db.models.fields.related_descriptors.create_reverse_many_to_one_manager.<locals>.RelatedManager|code-block|syntax|javascript|3463010|要从m2m关系访问查询集，正确的方法是使用.all()|3463011|print(p.submenus.all())|3463012|entityMap^0|C|D|0|K|H|17|E|1T|A|0|0|L|6|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|I|3|J|5|K|7|13|8|@]|D|@]|E|$L|M]]|$1|N|3|O|5|H|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|K|7|17|8|@]|D|@]|E|$L|M]]|$1|R|3|-4|5|H|7|18|8|@]|D|@]|E|$]]]|S|$]]

<blockquote>
 When I print the submenus the result is <code>app.Menu.None</code>
</blockquote>

This is happening because the OP is printing <code>print(p.submenus)</code> which is just a <code>RelatedManager</code>. It can be verified by checking the type of <code>p.submenus</code>:

<pre><code># this is what it prints in django 1.11
&gt;&gt;&gt; type(p.submenus) 
django.db.models.fields.related_descriptors.create_reverse_many_to_one_manager.&lt;locals&gt;.RelatedManager
</code></pre>

To access a queryset from the m2m relation, the correct way is to use <code>.all()</code>:

<pre><code>print(p.submenus.all())
</code></pre>

blocks|key|544482|text|例如，您有4级self，您需要这样的代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|544483|queryset+=+Menu.objects.filter(parent=None,+language__code=language,+menutype=menutype).order_by("order").prefetch_related('submenus',+'submenus__submenus',+'submenus__submenus__submenus',+"submenus__submenus__submenus__submenus")|code-block|syntax|javascript|544484|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For Example u have 4Level self u need code like this :
<pre><code>queryset = Menu.objects.filter(parent=None, language__code=language, menutype=menutype).order_by(&quot;order&quot;).prefetch_related('submenus', 'submenus__submenus', 'submenus__submenus__submenus', &quot;submenus__submenus__submenus__submenus&quot;)
</code></pre>

I have <code>Menu</code> model which has ForeignKey named parent related with itself.

If parent is None it means this menu is parent menu if it shows another Menu object it means it is submenu for its parent(many-to-one relation)

Here is my problem, I want to get all menus with its submenus using <code>prefetch_related</code>, How can I do it?

<blockquote>
 Note: I do not want to get submenus going database each time in for
 menu
</blockquote>

Here is my model class

<pre><code>class Menu(models.Model):
 title = models.CharField(max_length=30)
 language = models.ForeignKey(Language)
 parent = models.ForeignKey("self", default=None, blank=True, null=True, related_name="submenus")
</code></pre>

Here is my query

<pre><code>pm2 = Menu.objects.filter(parent=None, language__code=language, menutype=menutype).prefetch_related("submenus").order_by("order")
for p in pm2:
 print(p.title)
 print(p.submenus)
</code></pre>

When I print the submenus the result is <code>app.Menu.None</code>

How can I use prefetch_related in self related model

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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我有Menu模型，它的ForeignKey命名父级与自身相关。如果父菜单为None，则表示此菜单是父菜单，如果它显示另一个菜单对象，则意味着它是父菜单(多对一关系)的子菜单。这是我的问题，我想得到所有的菜单和它的子菜单使用prefetch_related，我怎么做呢？注意：我不想让子菜单每次都进入数据库这是我的模型课c...

问如何在自相关模型中使用prefetch_related
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问如何在自相关模型中使用prefetch_relatedEN