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    <p>So if you're using the acts-as-taggable-on gem and have the following models:</p> <pre><code>class User &lt; ActiveRecord::Base acts_as_tagger has_many :brand_users has_many :brands, :through =&gt; :brand_users end </code></pre> <p>So you also have the tables in your schema like:</p> <pre><code>create_table "users", :force =&gt; true do |t| t.string "name" end create_table "brands", :force =&gt; true do |t| t.string "name" end </code></pre> <p>Then the following SQL query should hopefully do what you want (?):</p> <pre><code>SELECT brands.* FROM brands WHERE brands.id NOT IN ( SELECT brands.id FROM brands INNER JOIN brand_users ON brand_users.brand_id = brands.id INNER JOIN taggings ON (taggings.tagger_id = brand_users.user_id AND taggings.tagger_type = 'User') WHERE brand_users.user_id = 1 AND taggings.taggable_id = brand_users.brand_id ) </code></pre> <p>To translate this into Rails ORM, I can't get any closer without hard coding the whole sub-select SQL string, something like:</p> <pre><code>class Brand &lt; ActiveRecord::Base has_many :brand_users has_many :users, :through =&gt; :brand_users scope :has_not_been_tagged_by_user, lambda {|user| where("brands.id NOT IN (SELECT brands.id FROM brands INNER JOIN brand_users ON brand_users.brand_id = brands.id INNER JOIN taggings ON (taggings.tagger_id = brand_users.user_id AND taggings.tagger_type = 'User') WHERE brand_users.user_id = ? AND taggings.taggable_id = brand_users.brand_id)", user.id) } end </code></pre> <p>(I know you could do this and then use ruby's <a href="https://stackoverflow.com/questions/4307411/not-in-rails">.map(&amp;:id).join(',')</a> but if this is a large app I think you loose a lot of performance by taking this out of the database, converting it into a string of integers and feeding it back in (as I understand it).)</p> <p>Then in your controller <strong>I think</strong> you'd do something like:</p> <p><code>@brand = current_user.brands.has_not_been_tagged_by_user(current_user)</code></p> <p>As an aside, I think this would actually then execute an SQL like below (is that right?):</p> <pre><code>SELECT brands.* FROM users INNER JOIN brand_users ON brand_users.user_id = users.id INNER JOIN brands ON brands.id = brand_users.brand_id WHERE brands.id NOT IN ( SELECT brands.id FROM brands INNER JOIN brand_users ON brand_users.brand_id = brands.id INNER JOIN taggings ON (taggings.tagger_id = brand_users.user_id AND taggings.tagger_type = 'User') WHERE brand_users.user_id = 1 AND taggings.taggable_id = brand_users.brand_id ) AND users.id = 1 </code></pre>
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    1. POHow can I filter my query to show instances where current user has no tags?
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    1. COThis works. Thanks so much!
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