blocks|key|839520|text|您可以将其封装在一个条件中，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|839521|def+save_thumbnail
++if+File.basename(thumb)+!=+thumbnail_file_name
++++self.update_attributes(
++++++:thumbnail_file_name+=>+File.basename(thumb),+
++++++:thumbnail_content_type+=>+'image/jpeg'
++++)
++end
end|code-block|syntax|javascript|839522|这样它就只会运行一次。|839523|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|$]]

You could wrap it in a conditional, something like:

<pre><code>def save_thumbnail
 if File.basename(thumb) != thumbnail_file_name
 self.update_attributes(
 :thumbnail_file_name =&gt; File.basename(thumb), 
 :thumbnail_content_type =&gt; 'image/jpeg'
 )
 end
end
</code></pre>

That way it would only run once.

blocks|key|839653|text|您可以将其作为before_save运行。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|839654|验证后，更新缩略图，然后让它继续保存，但只使用赋值方法|839655|before_save+:save_thumbnail
def+save_thumbnail
++self.thumbnail_file_name+=+File.basename(thumb),+
++self.thumbnail_content_type+=+'image/jpeg'
end|code-block|syntax|javascript|839656|因为它不会调用save，所以您不会递归，但它会在方法退出后立即保存。|839657|这样的东西应该可以工作，除非在保存后有明确的原因需要它。|839658|由于您不是在更新单独的对象，而是更新同一个对象，因此这也将为您节省数据库调用。这就是我如何做时间戳和类似的事情。|839659|entityMap^0|7|B|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|10|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|11|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|T|$]]

You can run it as a <code>before_save</code> instead.

After it has been validated, update the thumbnail, then let it go on to be saved, but just use the assignment methods

<pre><code>before_save :save_thumbnail
def save_thumbnail
 self.thumbnail_file_name = File.basename(thumb), 
 self.thumbnail_content_type = 'image/jpeg'
end
</code></pre>

Since that won't call save, you wont recurse, but it will immediately be saved after the method exits.

Something like that should work, unless there is an explicit reason you need it in after save.

Since you are not updating a separate object, but the same one, this will save you a database call as well. This is How i do timestamps and things like that too.

blocks|key|839679|text|Rails+2：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|839680|Model.send(:create_without_callbacks)
Model.send(:update_without_callbacks)|code-block|syntax|javascript|839681|Rails+3：|839682|Vote.skip_callback(:save,+:after,+:add_points_to_user)|839683|请参阅此问题：|839684|How+to+skip+ActiveRecord+callbacks?|offset|length|839685|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/1342761/how-to-skip-activerecord-callbacks^0|0|0|0|0|0|0|Z|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@]|9|@$O|14|P|15|1|16]]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

Rails 2:

<pre><code>Model.send(:create_without_callbacks)
Model.send(:update_without_callbacks)
</code></pre>

Rails 3:

<pre><code>Vote.skip_callback(:save, :after, :add_points_to_user)
</code></pre>

See this question:

<a href="https://stackoverflow.com/questions/1342761/how-to-skip-activerecord-callbacks">How to skip ActiveRecord callbacks?</a>

blocks|key|623895|text|您可以(也应该)检查是否确实需要更新缩略图：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|623896|after_save+:save_thumbnail
def+save_thumbnail
++if+capture_time_changed?+#assuming+capture_time+contains+time+when+the+thumbnail+has+to+be+captured
++++#generate+thumbnail...
++++self.update_attributes(
++++++:thumbnail_file_name+=>+File.basename(thumb),+
++++++:thumbnail_content_type+=>+'image/jpeg'
++++)
++end
end|code-block|syntax|javascript|623897|在这里你可以阅读更多关于“脏”属性的内容：http://apidock.com/rails/ActiveRecord/Dirty|offset|length|623898|虽然我不确定它是否仍然可以看到after_save中的属性更改。您可以使用成员变量来指示更改，以防它不能。|623899|entityMap|0|LINK|mutability|MUTABLE|url|http://apidock.com/rails/ActiveRecord/Dirty^0|0|0|L|17|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]]|A|$]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

You can(and should) check if you actually need to update the thumbnail:

<pre><code>after_save :save_thumbnail
def save_thumbnail
 if capture_time_changed? #assuming capture_time contains time when the thumbnail has to be captured
 #generate thumbnail...
 self.update_attributes(
 :thumbnail_file_name =&gt; File.basename(thumb), 
 :thumbnail_content_type =&gt; 'image/jpeg'
 )
 end
end
</code></pre>

Here you can read more about 'dirty' attributes: <a href="http://apidock.com/rails/ActiveRecord/Dirty" rel="nofollow">http://apidock.com/rails/ActiveRecord/Dirty</a>

Although I'm not sure if it still can see the attribute changes in after_save. You can use a member variable to indicate changes in case it can't.

blocks|key|623948|text|在Rails3%2B中，after_save回调中的任何update_attribute都会导致递归。应该做的是：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|623949|after_save+:updater!
#+Awesome+Ruby+code
#+...
#+...

private

++def+updater!
++++self.update_column(:column_name,+new_value)+#+This+will+skip+validation+gracefully.
++end|code-block|syntax|javascript|623950|这里有一些关于它的文档：https://guides.rubyonrails.org/active_record_callbacks.html#skipping-callbacks|623951|entityMap|0|LINK|mutability|MUTABLE|url|https://guides.rubyonrails.org/active_record_callbacks.html#skipping-callbacks^0|A|A|Q|G|0|0|C|26|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|D|@$9|11|A|12|1|13]]|E|$]]|$1|M|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Any <code>update_attribute</code> in an <code>after_save</code> callback will cause recursion, in Rails3+.
What should be done is:

<pre><code>after_save :updater!
# Awesome Ruby code
# ...
# ...

private

 def updater!
 self.update_column(:column_name, new_value) # This will skip validation gracefully.
 end
</code></pre>

Here is some documentation about it: <a href="https://guides.rubyonrails.org/active_record_callbacks.html#skipping-callbacks" rel="nofollow noreferrer">https://guides.rubyonrails.org/active_record_callbacks.html#skipping-callbacks</a>

I've got a model which has a video attached with <a href="https://github.com/thoughtbot/paperclip" rel="noreferrer">Paperclip</a>. After it saves I use the saved video to generate a thumbnail. I need to do this after every save, even when a new video hasn't been uploaded, because the user can change the time where the thumbnail is captured.

I am currently using after_post_process to do this, but it will only generate the thumbnail when uploading a file (this is a callback which is part of Paperclip).

I would ideally use an after_save callback like this:

<pre><code>after_save :save_thumbnail
def save_thumbnail
 #generate thumbnail...
 self.update_attributes(
 :thumbnail_file_name =&gt; File.basename(thumb), 
 :thumbnail_content_type =&gt; 'image/jpeg'
 )
end
</code></pre>

Unfortunately update_attributes calls save, which then calls the before_save callback causing an infinite loop. Is there a simple way to circumvent this behaviour?

How can I update attributes in after_save without causing a recursion in rails 2.3?

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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我有一个模型，它有一个附加的视频。保存后，我使用保存的视频生成缩略图。我需要在每次保存后执行此操作，即使新视频尚未上传，因为用户可以更改捕获缩略图的时间。我目前正在使用after_post_process来做这件事，但它只会在上传文件时生成缩略图(这是一个回调，是回调的一部分)。理想情况下，我会使用如下所示的after...

问如何在after_save中更新属性，而不会在rails 2.3中导致递归？
EN

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问如何在after_save中更新属性，而不会在rails 2.3中导致递归？EN