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PORails has_many :through and Setting Property on Join model
 

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    <p>Similar to <a href="https://stackoverflow.com/questions/408872/rails-has-many-through-find-by-extra-attributes-in-join-model">this question</a>, how do I set a property on the join model just before save in this context?</p> <pre><code>class Post &lt; ActiveRecord::Base has_many :post_assets has_many :assets, :through =&gt; :post_assets has_many :featured_images, :through =&gt; :post_assets, :class_name =&gt; "Asset", :source =&gt; :asset, :conditions =&gt; ['post_assets.context = ?', "featured"] end class PostAssets &lt; ActiveRecord::Base belongs_to :post belongs_to :asset # context is so we know the scope or role # the join plays validates_presences_of :context end class Asset &lt; ActiveRecord::Base has_many :post_assets has_many :posts, :through =&gt; :post_assets end </code></pre> <p>I just want to be able to do this:</p> <pre><code>@post = Post.create!(:title =&gt; "A Post") @post.featured_images &lt;&lt; Asset.create!(:title =&gt; "An Asset") # ... @post = Post.first @featured = @post.featured_images.first #=&gt; #&lt;Asset id: 1, title: "An Asset"&gt; @featured.current_post_asset #=&gt; #&lt;PostAsset id: 1, context: "featured"&gt; </code></pre> <p>How would that work? I've been banging my head over it all day :).</p> <p>What currently happens is when I do this:</p> <pre><code>@post.featured_images &lt;&lt; Asset.create!(:title =&gt; "An Asset") </code></pre> <p>Then the join model <code>PostAsset</code> that gets created never gets a chance to set <code>context</code>. How do I set that context property? It looks like this:</p> <pre><code>PostAsset.first #=&gt; #&lt;PostAsset id: 1, context: nil&gt; </code></pre> <p><strong>Update</strong>:</p> <p>I have created a test <a href="http://github.com/viatropos/acts-as-joinable" rel="nofollow noreferrer">gem</a> to try to isolate the problem. Is there an easier way to do this?!</p> <p>This <a href="http://github.com/viatropos/acts-as-joinable/blob/master/lib/acts_as_joinable/core.rb" rel="nofollow noreferrer">ActsAsJoinable::Core class</a> makes it so you can have many to many relationships with a context between them in the join model. And it adds helper methods. The basic <a href="http://github.com/viatropos/acts-as-joinable/blob/master/test/test_acts_as_joinable.rb" rel="nofollow noreferrer">tests</a> show basically what I'm trying to do. Any better ideas on how to do this properly?</p>
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    1. COThis also seems similar to my question earlier this week: http://stackoverflow.com/questions/3035064/updating-extra-attributes-in-a-has-many-through-relationship-using-rails I just retroactively change the join model. I assume there must be a callback, however, to do work on the join model before it is saved. +1 'cause I'm curious.
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    2. COthere is a `before_add` and `after_add` callback on the non-join model (so `assets` on the Post), but you can't really access the join model any way without calling `PostAsset.first(:conditions => {...})`. It seems like it's a missing feature in Rails after reading all the forums.
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      1. USLance Pollard
 

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