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<title>Module: ActiveRecord::NamedScope::ClassMethods</title>
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<td><strong>Module</strong></td>
<td class="class-name-in-header">ActiveRecord::NamedScope::ClassMethods</td>
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<td><strong>In:</strong></td>
<td>
<a href="../../../files/lib/active_record/named_scope_rb.html">
lib/active_record/named_scope.rb
</a>
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<h3 class="section-bar">Methods</h3>
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<a href="#M000366">named_scope</a>
<a href="#M000365">scopes</a>
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<h3 class="section-bar">Public Instance methods</h3>
<div id="method-M000366" class="method-detail">
<a name="M000366"></a>
<div class="method-heading">
<a href="ClassMethods.src/M000366.html" target="Code" class="method-signature"
onclick="popupCode('ClassMethods.src/M000366.html');return false;">
<span class="method-name">named_scope</span><span class="method-args">(name, options = {}, &block)</span>
</a>
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<div class="method-description">
<p>
Adds a class method for retrieving and querying objects. A scope represents
a narrowing of a database query, such as <tt>:conditions => {:color
=> :red}, :select => ‘shirts.*’, :include =>
:washing_instructions</tt>.
</p>
<pre>
class Shirt < ActiveRecord::Base
named_scope :red, :conditions => {:color => 'red'}
named_scope :dry_clean_only, :joins => :washing_instructions, :conditions => ['washing_instructions.dry_clean_only = ?', true]
end
</pre>
<p>
The above calls to <tt><a
href="ClassMethods.html#M000366">named_scope</a></tt> define class methods
Shirt.red and Shirt.dry_clean_only. Shirt.red, in effect, represents the
query <tt>Shirt.find(:all, :conditions => {:color =>
‘red’})</tt>.
</p>
<p>
Unlike <tt>Shirt.find(...)</tt>, however, the object returned by Shirt.red
is not an Array; it resembles the association object constructed by a
<tt>has_many</tt> declaration. For instance, you can invoke
<tt>Shirt.red.find(:first)</tt>, <tt>Shirt.red.count</tt>,
<tt>Shirt.red.find(:all, :conditions => {:size =>
‘small’})</tt>. Also, just as with the association objects,
named \<a href="ClassMethods.html#M000365">scopes</a> act like an Array,
implementing Enumerable; <tt>Shirt.red.each(&block)</tt>,
<tt>Shirt.red.first</tt>, and <tt>Shirt.red.inject(memo, &block)</tt>
all behave as if Shirt.red really was an Array.
</p>
<p>
These named \<a href="ClassMethods.html#M000365">scopes</a> are composable.
For instance, <tt>Shirt.red.dry_clean_only</tt> will produce all shirts
that are both red and dry clean only. Nested finds and calculations also
work with these compositions: <tt>Shirt.red.dry_clean_only.count</tt>
returns the number of garments for which these criteria obtain. Similarly
with <tt>Shirt.red.dry_clean_only.average(:thread_count)</tt>.
</p>
<p>
All \<a href="ClassMethods.html#M000365">scopes</a> are available as class
methods on the <a href="../Base.html">ActiveRecord::Base</a> descendant
upon which the \<a href="ClassMethods.html#M000365">scopes</a> were
defined. But they are also available to <tt>has_many</tt> associations. If,
</p>
<pre>
class Person < ActiveRecord::Base
has_many :shirts
end
</pre>
<p>
then <tt>elton.shirts.red.dry_clean_only</tt> will return all of
Elton‘s red, dry clean only shirts.
</p>
<p>
Named \<a href="ClassMethods.html#M000365">scopes</a> can also be
procedural:
</p>
<pre>
class Shirt < ActiveRecord::Base
named_scope :colored, lambda { |color|
{ :conditions => { :color => color } }
}
end
</pre>
<p>
In this example, <tt>Shirt.colored(‘puce’)</tt> finds all puce
shirts.
</p>
<p>
Named \<a href="ClassMethods.html#M000365">scopes</a> can also have
extensions, just as with <tt>has_many</tt> declarations:
</p>
<pre>
class Shirt < ActiveRecord::Base
named_scope :red, :conditions => {:color => 'red'} do
def dom_id
'red_shirts'
end
end
end
</pre>
<p>
For testing complex named \<a href="ClassMethods.html#M000365">scopes</a>,
you can examine the scoping options using the <tt>proxy_options</tt> method
on the proxy itself.
</p>
<pre>
class Shirt < ActiveRecord::Base
named_scope :colored, lambda { |color|
{ :conditions => { :color => color } }
}
end
expected_options = { :conditions => { :colored => 'red' } }
assert_equal expected_options, Shirt.colored('red').proxy_options
</pre>
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<a name="M000365"></a>
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<a href="ClassMethods.src/M000365.html" target="Code" class="method-signature"
onclick="popupCode('ClassMethods.src/M000365.html');return false;">
<span class="method-name">scopes</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
</div>
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