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POActive Relation: Retrieving records through an association?
 

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    <p>I have the following models:</p> <pre><code>class User &lt; ActiveRecord::Base has_many :survey_takings end class SurveyTaking &lt; ActiveRecord::Base belongs_to :survey def self.surveys_taken # must return surveys, not survey_takings where(:state =&gt; 'completed').map(&amp;:survey) end def self.last_survey_taken surveys_taken.maximum(:position) # that's Survey#position end end </code></pre> <p>The goal is to be able to call <code>@user.survey_takings.last_survey_taken</code> from a controller. (That's contrived, but go with it; the general goal is to be able to call class methods on <code>@user.survey_takings</code> that can use relations on the associated surveys.)</p> <p>In its current form, this code won't work; <code>surveys_taken</code> collapses the ActiveRelation into an array when I call <code>.map(&amp;:survey)</code>. Is there some way to instead return a relation for all the joined surveys? I can't just do this:</p> <pre><code>def self.surveys_taken Survey.join(:survey_takings).where("survey_takings.state = 'completed'") end </code></pre> <p>because <code>@user.survey_takings.surveys_taken</code> would join <em>all</em> the completed survey_takings, not just the completed survey_takings for <code>@user</code>.</p> <p>I guess what I want is the equivalent of</p> <pre><code>class User &lt; ActiveRecord::Base has_many :survey_takings has_many :surveys_taken, :through =&gt; :survey_takings, :source =&gt; :surveys end </code></pre> <p>but I can't access that surveys_taken association from <code>SurveyTaking.last_survey_taken</code>.</p>
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