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POSorting a Rails database table by a column in an associated model
 

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    <p>I'm trying to implement Ryan Bates' sortable table columns code (Railscast #228) but I'd like to be able to sort on an associated column. In particular, I have the following models and associations:</p> <pre><code>class Project &lt; ActiveRecord::Base belongs_to :program_manager, :class_name =&gt; "User" class User &lt; ActiveRecord::Base has_many :program_manager_projects, :class_name =&gt; "Project", :foreign_key =&gt; "program_manager_id" </code></pre> <p>The association between the Project model and the User model is mediated by the 'program_manager_id' foreign key, which the user sets in the new/edit views using a collection-select dropdown. Here's part of the annotation at the top of project.rb:</p> <pre><code># Table name: projects # program_manager_id :integer </code></pre> <p>I want to be able to sort my list of projects in the index view by the program manager's name, i.e., by project.program_manager.name.</p> <p>Ideally, I'd be able to point :order to this name somehow, perhaps with something like this in the index method of my ProjectsController:</p> <pre><code>@projects = Project.find(:all, :order =&gt; project.program_manager.name) </code></pre> <p>But that obviously won't work (not to mention Ryan's routine implements this with a specific reference to table names from the model to be sorted.)</p> <p>I've come across some intimidating approaches that use named_scope, such as:</p> <pre><code>named_scope :most_active, :select =&gt; "questions.*", :joins =&gt; "left join comments as comments_for_count on comments_for_count.question.id = questions.id", :group =&gt; "questions.id", :order =&gt; "count(questions.id) desc" </code></pre> <p>But given my lack of MySQL expertise, this is fairly impenetrable to me.</p> <p>Can anyone help me either generalize the named_scope example above for my specific case, or point me to a more straightforward strategy?</p> <p>Thanks very much,</p> <p>Dean</p>
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    1. COIt's a bad idea to use the ORM as an excuse to not learn SQL. Read up on joins. This seems like a good high-level overview: http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html
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    2. COPoint taken... and thanks for the helpful article link! I'll take your advice and stop procrastinating on digging into SQL.
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