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POHow can you validate the presence of a belongs to association with Rails?
 

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  1. POHow can you validate the presence of a belongs to association with Rails?
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    <p>Say I have a basic Rails app with a basic one-to-many relationship where each comment belongs to an article:</p> <pre><code>$ rails blog $ cd blog $ script/generate model article name:string $ script/generate model comment article:belongs_to body:text </code></pre> <p>Now I add in the code to create the associations, but I also want to be sure that when I create a comment, it always has an article:</p> <pre><code>class Article &lt; ActiveRecord::Base has_many :comments end class Comment &lt; ActiveRecord::Base belongs_to :article validates_presence_of :article_id end </code></pre> <p>So now let's say I'd like to create an article with a comment all at once:</p> <pre><code>$ rake db:migrate $ script/console </code></pre> <p>If you do this:</p> <pre><code>&gt;&gt; article = Article.new =&gt; #&lt;Article id: nil, name: nil, created_at: nil, updated_at: nil&gt; &gt;&gt; article.comments.build =&gt; #&lt;Comment id: nil, article_id: nil, body: nil, created_at: nil, updated_at: nil&gt; &gt;&gt; article.save! </code></pre> <p>You'll get this error:</p> <pre><code>ActiveRecord::RecordInvalid: Validation failed: Comments is invalid </code></pre> <p>Which makes sense, because the comment has no page_id yet. </p> <pre><code>&gt;&gt; article.comments.first.errors.on(:article_id) =&gt; "can't be blank" </code></pre> <p>So if I remove the <code>validates_presence_of :article_id</code> from <code>comment.rb</code>, then I could do the save, but that would also allow you to create comments without an article id. What's the typical way of handling this?</p> <p><strong>UPDATE</strong>: Based on Nicholas' suggestion, here's a implementation of save_with_comments that works but is ugly:</p> <pre><code>def save_with_comments save_with_comments! rescue false end def save_with_comments! transaction do comments = self.comments.dup self.comments = [] save! comments.each do |c| c.article = self c.save! end end true end </code></pre> <p>Not sure I want add something like this for every one-to-many association. Andy is probably correct in that is just best to avoid trying to do a cascading save and use the nested attributes solution. I'll leave this open for a while to see if anyone has any other suggestions. </p>
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