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PORails active record query: Find records on one side of a has_many :through that haven't been used with a particular record on the other side
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  1. PORails active record query: Find records on one side of a has_many :through that haven't been used with a particular record on the other side
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    copied!<p>I have a has_many :through relationship set up like so</p> <pre><code>class Situation &lt; ActiveRecord::Base has_many :notifications has_many :notiftypes, through: :notifications end class Notification &lt; ActiveRecord::Base belongs_to :situation belongs_to :notiftype end class Notiftype &lt; ActiveRecord::Base has_many :notifications has_many :situations, through: :notifications end </code></pre> <p>So, a Situation has many Notifications, which can be of many types (Notiftype).</p> <p>My problem is trying to query for the <code>notiftypes</code> that have not been set for a particular <code>situation</code>.</p> <p><a href="https://stackoverflow.com/questions/5319400/want-to-find-records-with-no-associated-records-in-rails-3">Want to find records with no associated records in Rails 3</a></p> <p>The answers in that question get me close, but only to the point of finding Notiftypes that have not been set AT ALL.</p> <p>If this were the standard <code>:situation</code> has_many <code>:notiftypes</code> I could just do a Left Outer Join like so</p> <pre><code>myquery = Notiftype.joins('LEFT OUTER JOIN situations ON situations.notiftype_id = notiftype.id').where('notiftype_id IS NULL') </code></pre> <p>but I'm really not sure how to do this with the intermediate table between them. </p> <p>I have been trying consecutive joins but it's not working. I'm not sure how to join the two separated tables.</p> <p>Can anyone explain the right way to query the db? I am using SQLite, Rails 3.1, Ruby 1.9.2 right now, but likely Postgresql in the future.</p>
 

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