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    <p>I think you want to read about <strong><a href="http://guides.rubyonrails.org/active_record_querying.html#eager-loading-associations" rel="nofollow">Eager Loading Associations</a></strong>.</p> <pre><code>@images = Image.includes(:location).where("images.user_id = ?", 5) </code></pre> <p>This will find <code>Image</code> instances where <code>user_id = 5</code>. It then runs a 2nd query that will <code>JOIN</code> and build the associated <code>Location</code> instance <em>(thats what the <code>.includes(:location)</code> will do for you)</em>.</p> <p>This more closely matches your alternative query, as it does select all columns from <code>images</code> and <code>location</code> tables.</p> <p>You can build an Array based on this containing a hash with only the keys you're interested in through something like this.</p> <pre><code>@hash_object = @images.collect { |i| { caption: i.caption, latitude: i.location.latitude, longitude: i.location.longitude } } </code></pre> <hr> <p>If you want to build this with only a single query, you can use <code>.joins(:location)</code> in combination with <code>.includes(:location)</code></p> <pre><code>Image.joins(:location).includes(:location).where("images.user_id = ?", 5) </code></pre> <p><strong>Important:</strong> This will omit <code>Image</code> instances who have no assoicated <code>Location</code>. You can modify the <code>joins()</code> a bit to help with this, but the above will have this omission.</p> <hr> <p>If you <strong>really</strong> want only specific columns to be selected, read up on <strong><a href="http://guides.rubyonrails.org/active_record_querying.html#selecting-specific-fields" rel="nofollow">Selecting Specific Columns</a></strong> though there are warnings for the use of this</p> <blockquote> <p>If the select method is used, all the returning objects will be read only.</p> </blockquote> <p>and</p> <blockquote> <p>Be careful because this also means you’re initializing a model object with only the fields that you’ve selected.</p> </blockquote> <hr> <p>In Rails master (not out in 3.2.11) you can pass <em>multiple columns</em> to <a href="https://github.com/rails/rails/blob/master/activerecord/lib/active_record/relation/calculations.rb#L111" rel="nofollow"><code>.pluck()</code></a> but this appears to only be restricted to a single table <em>(you wouldn't be able to get the <code>locations</code> table's <code>:latitude</code> and <code>:longitude</code> when plucking from <code>Image</code>)</em>. It's good to know about though.</p>
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    1. POQuery data from two associated tables
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    1. COThanks, that works! Much better than the query in a loop that was happening before. I notice in the logs it's still querying the Location and Image tables separately in two queries though; I wonder if there's a way around that. Thanks again for the help!
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    2. COUpdated my answer for you. Please, accept/up-vote my answer if it's fixed your problem.
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    3. COThanks a bunch!
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