blocks|key|1439876|text|有两种方法可以做到这一点；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1439877|try:
++++foo+=+Foo.objects.get(bar=baz)
except+model.DoesNotExist:
++++foo+=+None|code-block|syntax|javascript|1439878|或者，您可以使用包装器：|1439879|def+get_or_none(model,+*args,+**kwargs):
++++try:
++++++++return+model.objects.get(*args,+**kwargs)
++++except+model.DoesNotExist:
++++++++return+None|1439880|这样叫它|1439881|foo+=+get_or_none(Foo,+baz=bar)|1439882|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

There are two ways to do this;

<pre><code>try:
 foo = Foo.objects.get(bar=baz)
except model.DoesNotExist:
 foo = None
</code></pre>

Or you can use a wrapper:

<pre><code>def get_or_none(model, *args, **kwargs):
 try:
 return model.objects.get(*args, **kwargs)
 except model.DoesNotExist:
 return None
</code></pre>

Call it like this

<pre><code>foo = get_or_none(Foo, baz=bar)
</code></pre>

blocks|key|1225223|text|给Foo+its+custom+manager。这非常简单-只需将您的代码放入自定义管理器的函数中，在模型中设置自定义管理器，然后使用Foo.objects.your_new_func(...)调用它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1225224|如果您需要泛型函数(在任何模型上使用它，而不仅仅是自定义管理器)，请编写您自己的函数，并将其放在您的python路径上的某个位置并导入，这样就不会再混乱了。|1225225|entityMap|0|LINK|mutability|MUTABLE|url|http://www.djangoproject.com/documentation/models/custom_managers/^0|1V|U|5|I|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

Give Foo <a href="http://www.djangoproject.com/documentation/models/custom_managers/" rel="nofollow noreferrer">its custom manager</a>. It's pretty easy - just put your code into function in custom manager, set custom manager in your model and call it with <code>Foo.objects.your_new_func(...)</code>.

If you need generic function (to use it on any model not just that with custom manager) write your own and place it somewhere on your python path and import, not messy any more.

blocks|key|1440048|text|为了在sorki的回答中添加一些示例代码(我想将此作为评论添加，但这是我的第一篇文章，我没有足够的声誉来留下评论)，我实现了一个get_or_none自定义管理器，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1440049|from+django.db+import+models

class+GetOrNoneManager(models.Manager):
++++"""Adds+get_or_none+method+to+objects
++++"""
++++def+get_or_none(self,+**kwargs):
++++++++try:
++++++++++++return+self.get(**kwargs)
++++++++except+self.model.DoesNotExist:
++++++++++++return+None

class+Person(models.Model):
++++name+=+models.CharField(max_length=255)
++++objects+=+GetOrNoneManager()|code-block|syntax|javascript|1440050|现在我可以这样做了：|1440051|bob_or_none+=+Person.objects.get_or_none(name='Bob')|1440052|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

To add some sample code to sorki's answer (I'd add this as a comment, but this is my first post, and I don't have enough reputation to leave comments), I implemented a get_or_none custom manager like so:

<pre><code>from django.db import models

class GetOrNoneManager(models.Manager):
 """Adds get_or_none method to objects
 """
 def get_or_none(self, **kwargs):
 try:
 return self.get(**kwargs)
 except self.model.DoesNotExist:
 return None

class Person(models.Model):
 name = models.CharField(max_length=255)
 objects = GetOrNoneManager()
</code></pre>

And now I can do this:

<pre><code>bob_or_none = Person.objects.get_or_none(name='Bob')
</code></pre>

blocks|key|1225385|text|无论是通过管理器还是泛型函数，您可能还希望在TRY语句中捕获'MultipleObjectsReturned‘，因为如果您的kwargs检索多个对象，则get()函数将引发此问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1225386|在泛型函数基础上构建：|1225387|def+get_unique_or_none(model,+*args,+**kwargs):
++++try:
++++++++return+model.objects.get(*args,+**kwargs)
++++except+(model.DoesNotExist,+model.MultipleObjectsReturned),+err:
++++++++return+None|code-block|syntax|javascript|1225388|在管理器中：|1225389|class+GetUniqueOrNoneManager(models.Manager):
++++"""Adds+get_unique_or_none+method+to+objects
++++"""
++++def+get_unique_or_none(self,+*args,+**kwargs):
++++++++try:
++++++++++++return+self.get(*args,+**kwargs)
++++++++except+(self.model.DoesNotExist,+self.model.MultipleObjectsReturned),+err:
++++++++++++return+None|1225390|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Whether doing it via a manager or generic function, you may also want to catch 'MultipleObjectsReturned' in the TRY statement, as the get() function will raise this if your kwargs retrieve more than one object.

Building on the generic function:

<pre><code>def get_unique_or_none(model, *args, **kwargs):
 try:
 return model.objects.get(*args, **kwargs)
 except (model.DoesNotExist, model.MultipleObjectsReturned), err:
 return None
</code></pre>

and in the manager:

<pre><code>class GetUniqueOrNoneManager(models.Manager):
 """Adds get_unique_or_none method to objects
 """
 def get_unique_or_none(self, *args, **kwargs):
 try:
 return self.get(*args, **kwargs)
 except (self.model.DoesNotExist, self.model.MultipleObjectsReturned), err:
 return None
</code></pre>

blocks|key|1225446|text|您也可以尝试使用django恼人(它还有另一个有用的功能！)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1225447|使用以下命令进行安装：|1225448|pip+install+django-annoying

from+annoying.functions+import+get_object_or_None
get_object_or_None(Foo,+bar=baz)|code-block|syntax|javascript|1225449|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

You can also try to use django annoying (it has another useful functions!)

install it with:

<pre><code>pip install django-annoying

from annoying.functions import get_object_or_None
get_object_or_None(Foo, bar=baz)
</code></pre>

blocks|key|1440223|text|我认为在大多数情况下，你可以直接使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1440224|foo,+created+=+Foo.objects.get_or_create(bar=baz)|code-block|syntax|javascript|1440225|仅当在Foo表中添加新条目并不重要时(其他列将具有无/缺省值)|1440226|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I think that in most cases you can just use:

<pre><code>foo, created = Foo.objects.get_or_create(bar=baz)
</code></pre>

Only if it is not critical that a new entry will be added in Foo table ( other columns will have the None/default values )

Is there any Django function which will let me get an object form the database, or None if nothing matches?

Right now I'm using something like:

<pre><code>foo = Foo.objects.filter(bar=baz)
foo = len(foo) &gt; 0 and foo.get() or None
</code></pre>

But that's not very clear, and it's messy to have everywhere.

Django: Get an object form the DB, or 'None' if nothing matches

数据库

Django

有没有什么Django函数可以让我从数据库中获取一个对象，或者如果没有匹配的话就没有？现在我使用的是这样的东西：foo = Foo.objects.filter(bar=baz)foo = len(foo) > 0 and foo.get() or None但这并不是很清楚，而且到处都是乱七八糟的。

问Django:从DB获取一个对象，如果没有匹配，则为'None‘
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