blocks|key|3075830|text|简而言之:除非迫不得已，否则不要使用default_scope。使用命名作用域可能会更好。也就是说，如果需要，您可以使用with_exclusive_scope覆盖默认作用域。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3075831|有关更多详细信息，请查看this+question。|3075832|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/1648971/rails-why-is-withexclusivescope-protected-any-good-practice-on-how-to-use-it^0|I|D|1O|K|0|C|D|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@$9|V|A|W|1|X]]|E|$]]|$1|H|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

Short answer: Do not use <code>default_scope</code> unless you really have to. You'll probably be better off with named scopes. With that said, you can use <code>with_exclusive_scope</code> to override the default scope if you need to.

Have a look at <a href="https://stackoverflow.com/questions/1648971/rails-why-is-withexclusivescope-protected-any-good-practice-on-how-to-use-it">this question</a> for more details.

blocks|key|321841|text|您可以使用with_exclusive_scope方法覆盖默认作用域。所以：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|321842|foos+=+Foo.with_exclusive_scope+{+:conditions+=>+["baz+=+?",+baz]+}|code-block|syntax|javascript|321843|321844|with_exclusive_scope+documentation|unordered-list-item|321845|321846|entityMap|0|LINK|mutability|MUTABLE|url|http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M002312^0|5|K|0|0|0|0|K|0|K|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|11|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|12|8|@$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]]|E|$]]|$1|O|3|-4|5|6|7|18|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|Q|$R|$5|S|T|U|E|$V|W]]]]

You can override a default scope using the <code>with_exclusive_scope</code> method. So:

<pre><code>foos = Foo.with_exclusive_scope { :conditions =&gt; ["baz = ?", baz] }
</code></pre>

<ul>
<li><a href="http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M002312" rel="nofollow noreferrer"><code>with_exclusive_scope</code></a> documentation</li>
</ul>

blocks|key|3289263|text|在Rails+3中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3289264|foos+=+Foo.unscoped.where(:baz+=>+baz)|code-block|syntax|javascript|3289265|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|$]]

In Rails 3:

<pre><code>foos = Foo.unscoped.where(:baz =&gt; baz)
</code></pre>

blocks|key|321848|text|Rails+3的default_scope似乎不会像在Rails+2中那样被覆盖。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|321849|例如：|321850|class+Foo+<+ActiveRecord::Base
++belongs_to+:bar
++default_scope+:order=>"created_at+desc"
end

class+Bar+<+ActiveRecord::Base
++has_many+:foos
end

>+Bar.foos
++SELECT+*+from+Foo+where+bar_id+=+2+order+by+"created_at+desc";
>+Bar.unscoped.foos
++SELECT+*+from+Foo;++(WRONG!++removes+the+"has"+relationship)
>+Bar.foos(+:order=>"created_at+asc"+)++#+trying+to+override+ordering
++SELECT+*+from+Foo+where+bar_id+=+2+order+by+"created_at+desc,+created_at+asc"|code-block|syntax|javascript|321851|在我的应用程序中，使用PostgreSQL，默认作用域中的排序胜出。我删除了所有的default_scopes，并在任何地方显式地对其进行编码。|321852|陷阱Rails3！|321853|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]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Rails 3 default_scope does not appear to get overridden like it did in Rails 2. 

e.g. 

<pre><code>class Foo &lt; ActiveRecord::Base
 belongs_to :bar
 default_scope :order=&gt;"created_at desc"
end

class Bar &lt; ActiveRecord::Base
 has_many :foos
end

&gt; Bar.foos
 SELECT * from Foo where bar_id = 2 order by "created_at desc";
&gt; Bar.unscoped.foos
 SELECT * from Foo; (WRONG! removes the "has" relationship)
&gt; Bar.foos( :order=&gt;"created_at asc" ) # trying to override ordering
 SELECT * from Foo where bar_id = 2 order by "created_at desc, created_at asc"
</code></pre>

In my app, using PostgreSQL, the ordering in the default scope WINS. I'm removing all of my default_scopes and coding it in explicitly everywhere. 

Pitfall Rails3!

blocks|key|3075889|text|如果您只需要更改default_scope中定义的顺序，则可以使用reorder+method。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3075890|class+Foo+<+ActiveRecord::Base
++default_scope+order('created_at+desc')
end

Foo.reorder('created_at+asc')|code-block|syntax|javascript|3075891|运行以下SQL：|3075892|SELECT+*+FROM+"foos"+ORDER+BY+created_at+asc|3075893|entityMap|0|LINK|mutability|MUTABLE|url|http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-reorder^0|8|D|X|7|X|E|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|15|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

If all you need is to change the order defined in <code>default_scope</code>, you can use the <a href="http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-reorder" rel="noreferrer"><code>reorder</code> method</a>.

<pre><code>class Foo &lt; ActiveRecord::Base
 default_scope order('created_at desc')
end

Foo.reorder('created_at asc')
</code></pre>

runs the following SQL:

<pre><code>SELECT * FROM "foos" ORDER BY created_at asc
</code></pre>

blocks|key|321859|text|由于4.1，您可以使用ActiveRecord::QueryMethods#unscope来对抗默认作用域：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|321860|class+User+<+ActiveRecord::Base
++default_scope+{+where+tester:+false+}
++scope+:testers,+->+{+unscope(:where).where+tester:+true+}
++scope+:with_testers,+->+{+unscope(:where).where+tester:+[true,+false]+}
++#+...
end|code-block|syntax|javascript|321861|这是currently有可能的东西：unscope：:where,+:select,+:group,+:order,+:lock,+:limit,+:offset,+:joins,+:includes,+:from,+:readonly,+:having。|321862|但是，如果可以的话，请避免使用default_scope。这是为你好。|321863|entityMap|0|LINK|mutability|MUTABLE|url|http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-unscope|1|https://github.com/rails/rails/blob/cfa53cc0fde7ca5a310673b4740ab908e8d5f38e/activerecord/lib/active_record/relation/query_methods.rb#L331^0|2|3|B|Y|B|Y|0|0|0|I|7|Q|2T|2|9|1|0|F|D|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|17|8|@$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|M|3|N|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

Since <code>4.1</code> you can use <a href="http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-unscope"><code>ActiveRecord::QueryMethods#unscope</code></a> to fight default scope:

<pre><code>class User &lt; ActiveRecord::Base
 default_scope { where tester: false }
 scope :testers, -&gt; { unscope(:where).where tester: true }
 scope :with_testers, -&gt; { unscope(:where).where tester: [true, false] }
 # ...
end
</code></pre>

It is <a href="https://github.com/rails/rails/blob/cfa53cc0fde7ca5a310673b4740ab908e8d5f38e/activerecord/lib/active_record/relation/query_methods.rb#L331">currently</a> possible to <code>unscope</code> stuff like: <code>:where, :select, :group, :order, :lock, :limit, :offset, :joins, :includes, :from, :readonly, :having</code>.

But still please avoid using of <code>default_scope</code> if you can. It's for your own good.

blocks|key|323699|text|对于Rails+3%2B，您可以结合使用unscoped和merge：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|323700|#+model+User+has+a+default+scope
query+=+User.where(email:+"foo@example.com")

#+get+rid+of+default+scope+and+then+merge+the+conditions
query+=+query.unscoped.merge(query)|code-block|syntax|javascript|323701|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|$]]

With Rails 3+ you can use a combination of unscoped and merge:

<pre><code># model User has a default scope
query = User.where(email: "foo@example.com")

# get rid of default scope and then merge the conditions
query = query.unscoped.merge(query)
</code></pre>

blocks|key|323703|text|那么，您可以始终使用旧的收藏夹find_by_sql与完整的查询。例如:+Model.find_by_sql("SELECT+*+FROM+models+id=123")|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|323704|entityMap^0|F|B|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

Well, you can always use the old time favorite <code>find_by_sql</code> with the complete query. 
For example:
 Model.find_by_sql("SELECT * FROM models WHERE id=123")

blocks|key|3075944|text|在Rails+5.1%2B+(可能是更早的版本，但我已经测试过它在5.1上可以工作)上，可以取消特定列的作用域，imho是以一种可以在命名作用域中使用的方式删除default_scope的理想解决方案。在OPs+default_scope的情况下，|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3075945|Foo.unscope(where:+:bar)|code-block|syntax|javascript|3075946|或|3075947|scope+:not_default,+->+{+unscope(where:+:bar)+}
Foo.not_default|3075948|都会导致sql查询不应用原始作用域，但会应用合并到arel中的任何其他条件。|3075949|entityMap^0|26|D|2W|D|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|10|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|R|$]]

On Rails 5.1+ (and maybe earlier, but I've tested it works on 5.1) it is possible to unscope a specific column, which imho is the ideal solution for removing a <code>default_scope</code> in a fashion that can be used inside a named scope. In the case of the OPs <code>default_scope</code>,

<pre><code>Foo.unscope(where: :bar)
</code></pre>

Or

<pre><code>scope :not_default, -&gt; { unscope(where: :bar) }
Foo.not_default
</code></pre>

Will both result in a sql query that doesn't apply the original scope, but does apply whatever other conditions get merged into the arel.

If I have an ActiveRecord::Base model with a default-scope:

<pre><code>class Foo &lt; ActiveRecord::Base

 default_scope :conditions =&gt; ["bar = ?",bar]

end
</code></pre>

Is there any way to do a <code>Foo.find</code> without using the <code>default_scope</code> conditions? In other words, can you override a default scope?

I would have thought that using 'default' in the name would suggest that it was overridable, otherwise it would be called something like <code>global_scope</code>, right?

Overriding a Rails default_scope

PostgreSQL

如果我有一个具有default-scope的ActiveRecord：：基础模型：class Foo < ActiveRecord::Base default_scope :conditions => ["bar = ?",bar]end有没有办法在不使用default_scope条件的情况下执行Foo.find？换...

问覆盖Rails default_scope
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