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POIdentifying Model Instance by Two Relations
 

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  1. POIdentifying Model Instance by Two Relations
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    <p>I'm trying to pick out an instance of a model ("Package") by its relation to two other models to which it belongs ("Cut" and "Animal"). While there are, say many packages with :cut_id 3 and many with :animal_id 4, there should only be one with both, and I want to pick that one out and display its contents in a table. </p> <p>I've tried the following DIY mess, and it's not really working. (cutfind is a method I created that I know works for calling out all of the cuts associated with the given animal.)</p> <pre><code>&lt;% @animal.cutfind.each do |cut| %&gt; &lt;tr&gt; &lt;td&gt;&lt;%= cut.name %&gt;&lt;/td&gt; &lt;td&gt;&lt;%= number_to_currency(cut.price) %&gt;&lt;/td&gt; &lt;td&gt;&lt;%= cut.package_weight %&gt; lb&lt;/td&gt; &lt;% @a = Package.where(:animal_id =&gt; @animal.id) %&gt; &lt;% @pset = @a.where(:cut_id =&gt; cut.id) %&gt; &lt;% @pset.each do |p| %&gt; &lt;td&gt;&lt;%= p.original %&gt;&lt;/td&gt; &lt;td&gt;&lt;%= p.left %&gt;&lt;/td&gt; &lt;% end %&gt; &lt;/tr&gt; &lt;%end%&gt; </code></pre> <p>Any idea how to do this [better]? Thanks.</p> <p>Update: I tried this other DIY mess and am getting the same problem (the cells aren't even being created, which leads me to believe that @pset is empty).</p> <p>This is in my animal model:</p> <pre><code>def packagefind Package.where(:animal_id =&gt; self.id) end </code></pre> <p>And then I changed the above like so: </p> <pre><code>&lt;td&gt;&lt;%= cut.package_weight %&gt; lb&lt;/td&gt; &lt;% @pset = @animal.packagefind.where(:cut_id =&gt; cut.id) %&gt; &lt;% @pset.each do |p| %&gt; &lt;td&gt;&lt;%= p.original %&gt;&lt;/td&gt; &lt;td&gt;&lt;%= p.left %&gt;&lt;/td&gt; &lt;% end %&gt; </code></pre>
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    1. COThere's a potential problem with your HTML layout. Each row (tr) of a table should have the same number of data cells (td), but @pset isn't guaranteed to have the same number of elements in each row, right? So the number of cells may vary.
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    2. COPset would actually be the same every time. The each block is just my hacky way of dealing with the fact that I was getting a list of (1) elements, instead of a single element. I ran into this problem before when using blank.where(etc), because it always returns a list, even if it's guaranteed (as here) to be a single element.
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    3. COThis is for the below, cause it wouldn't let me add comments there (!?). So it doesn't quite work. I now get an error saying that @p (which I assigned to Package.find_by_cut_id_and_animal_id(cut.id, @animal.id), is of NilClass, which is sort of weird. Does this likely have to do with architecture differences?
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