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POGet ids of elements in a named scope
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  1. POGet ids of elements in a named scope
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    copied!<p>In ruby on rails, all <code>has_many :widgets</code> methods generate both a <code>object.widgets</code> method and an <code>object.widget_ids</code> method.</p> <p>The latter method is very useful because it bypasses the creation of ActiveRecord objects and runs a much faster query. The query speed can be improved by using the <code>:select</code> option, but ruby still allocates much more memory when generating objects instead of integers.</p> <p>For example</p> <pre><code>User has_many :historical_sessions: &gt;&gt; Benchmark.measure { User.find(4).historical_sessions.map(&amp;:id) } HistoricalSession Load (131.0ms) SELECT * FROM `historical_sessions` WHERE (`historical_sessions`.user_id = 4) =&gt; #&lt;Benchmark::Tms:0xbe805c0 @cutime=0.0, @label="", @total=1.996, @stime=0.0150000000000006, @real=2.09599995613098, @utime=1.981, @cstime=0.0&gt; (2.1 seconds) &gt;&gt; Benchmark.measure { User.find(4).historical_session_ids } HistoricalSession Load (34.0ms) SELECT `historical_sessions`.id FROM `historical_sessions` WHERE (`historical_sessions`.user_id = 4) =&gt; #&lt;Benchmark::Tms:0x11e6cd94 @cutime=0.0, @label="", @total=1.529, @stime=0.032, @real=1.55099987983704, @utime=1.497, @cstime=0.0&gt; (1.6 seconds) </code></pre> <p>(The result set is 67353 objects)</p> <p>Is there a way to have the same behavior occur when using named_scopes?</p> <p>For example,</p> <pre><code>User named_scope :recent User.recent (Exists) User.recent_ids (Does not exist) </code></pre> <p>The way I currently get the ids of objects in a named scope result set is: HistoricalSession.recent.map(&amp;:id). This is essentially similar to what is done in the latter example above, and is obviously not efficient. I do not want to build entire HistoricalSession objects when in the end all I need is an array of ids.</p> <p>An alternate implementation could be a new .find method. For example, HistoricalSession.recent.find_attributes(:id). This method would replace the select statement to only select the specified values and would short circuit ActiveRecord object creation to just return an array.</p> <p>Any suggestions? Might this be a simple plugin to write?</p>
 

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