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POConfused about Rails has_and_belongs_to_many Association
 

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  1. POConfused about Rails has_and_belongs_to_many Association
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    <p>I have two models, items and categories which have a many-to-many relationship using the has_and_belongs_to_many association.</p> <p>In my models I have</p> <pre><code>class Item &lt; ActiveRecord::Base has_and_belongs_to_many :categories end </code></pre> <p>and </p> <pre><code>class Category &lt; ActiveRecord::Base has_and_belongs_to_many :items end </code></pre> <p>I created a join table "categories_items":</p> <pre><code>create_table "categories_items", :id =&gt; false, :force =&gt; true do |t| t.integer "category_id" t.integer "item_id" end </code></pre> <p>I'm not getting any errors, but I'm just a bit confused about exactly what the association allows. Right now, if I have some category @category, I can find all the Items in it by doing </p> <pre><code>@category.items </code></pre> <p>I assumed that I could find the categories associated with a given Item @item by doing</p> <pre><code>@item.categories </code></pre> <p>However I get an error that says ActiveModel::MissingAttributeError: missing attribute: category</p> <p>Am I misunderstanding how a has_and_belongs_to_many association functions, or am I missing something in my code? Thank you!</p> <p>Edit - Additional Information:</p> <p>I think the confusion lies in how I'm supposed to assign items/categories. Currently, I'm creating them independently: </p> <pre><code>@item = Item.new ... add attributes ... @item.save </code></pre> <p>and </p> <pre><code>@category = Category.new ... add attributes ... @category.save </code></pre> <p>and then associating them with</p> <pre><code>@category.items &lt;&lt; @item @item.categories &lt;&lt; @category </code></pre>
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    1. COWhat you have here looks ok, and the association *should* work both ways. How is `@item` being assigned?
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    2. COI just pasted your code into a test project (Rails 3.2.1) and the association worked fine for me both ways.
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      1. USDon Cruickshank
    3. COUsually the MissingAttribute exception is thrown when you do a Model.select("something").first.somethingelse. Can you paste in a git the code you're running and the backtrace?
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