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    <p>Use select() to name the columns you want. At least this works in Rails 3.0.9.</p> <p>Background: my application has a primary table named :rights. I wanted to be able to ascribe a tag and color to a given :right record so I could easily pick it out of an index listing. This doesn't cleanly fit the Rails picture of associated records; most :rights will never be tagged, and the tags are completely arbitrary (user input via tag/edit). </p> <p>I could try duplicating the tag data in the :right record, but that violates normal form. Or I could try querying :tags for each :right record, but that is a painfully inefficient approach. I want to be able to join the tables.</p> <p>MySQL console shows:</p> <pre><code>mysql&gt; describe rights; +------------+---------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------+---------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | ... | Tagid | int(11) | YES | | NULL | | +------------+---------------+------+-----+---------+----------------+ mysql&gt; describe tags; +------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | TagName | varchar(255) | YES | | NULL | | | TagColor | varchar(255) | YES | | NULL | | | created_at | datetime | YES | | NULL | | | updated_at | datetime | YES | | NULL | | +------------+--------------+------+-----+---------+----------------+ </code></pre> <p>I am going to use TagName and TagColor in views/rights/index.html.erb, so I want the rights controller to include those columns in the @rights object it passes to the view. Since not every :right has a :tag, I want to use an outer join:</p> <pre><code>@rights = Right.joins("LEFT OUTER JOIN tags ON rights.Tagid = tags.id") </code></pre> <p>But, as everyone has found, this alone doesn't work: a block reference to TagName produces a server error. However, if I add a select at the end, all is well:</p> <pre><code>@rights = Right.joins("LEFT OUTER JOIN tags ON rights.Tagid = tags.id").select("rights.*,tags.TagName as TagName,tags.TagColor as TagColor") </code></pre> <p>Note added 6/7/13: the select clause does not require aliases - this works too:</p> <pre><code>.select("rights.*,tags.TagName,tags.TagColor") </code></pre> <p>Now I can reference TagName and TagColor in my view:</p> <pre><code>&lt;% @rights.each do |right| %&gt; &lt;tr ALIGN=Left &lt;%= # color background if this is tagged " BGCOLOR=#{right.TagColor}" if right.TagColor %&gt; &gt; ... &lt;% end %&gt; </code></pre>
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