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PORails ActiveRecord associations inconsistently updated
 

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  1. PORails ActiveRecord associations inconsistently updated
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    <p>I am running into some Rails 2.3.5 ActiveRecord behavior I do not understand. It appears that an object can have its association ids updated in inconsistent ways. </p> <p>This is best explained with an example:</p> <p>Create a <code>Post</code> model with the string attribute <code>'title'</code> and a <code>Comment</code> model with the string attribute <code>'content'</code>. </p> <p>Here are the associations: </p> <pre><code>class Post &lt; ActiveRecord::Base has_many :comments end class Comment &lt; ActiveRecord::Base belongs_to :post end </code></pre> <p>Scenario #1: In the following code I create one <code>Post</code> with an associated <code>Comment</code>, create a second <code>Post</code> by <code>find</code>'ing the first, add a second <code>Comment</code> to the first <code>Post</code> and discover that the second <code>Post</code> has the second <code>Comment</code> associated to it without an explicit assignment.</p> <pre><code>post1 = Post.new post1 = Post.new(:title =&gt; 'Post 1') comment1 = Comment.new(:content =&gt; 'content 1') post1.comments &lt;&lt; comment1 post1.save # Create a second Post object by find'ing the first post2 = Post.find_by_title('Post 1') # Add a new Comment to the first Post object comment2 = Comment.new(:content =&gt; 'content 2') post1.comments &lt;&lt; comment2 # Note that both Comments are associated with both Post objects even # though I never explicitly associated it with post2. post1.comment_ids # =&gt; [12, 13] post2.comment_ids # =&gt; [12, 13] </code></pre> <p>Scenario #2: Run the above commands again but this time insert one extra command that, on the face of it, should not affect the results. The extra command is <code>post2.comments</code> which occurs <em>after</em> creating <code>comment2</code> and <em>before</em> adding <code>comment2</code> to <code>post1</code>. </p> <pre><code>post1 = Post.new post1 = Post.new(:title =&gt; 'Post 1A') comment1 = Comment.new(:content =&gt; 'content 1A') post1.comments &lt;&lt; comment1 post1.save # Create a second Post object by find'ing the first post2 = Post.find_by_title('Post 1A') # Add a new Comment to the first Post object comment2 = Comment.new(:content =&gt; 'content 2A') post2.comments # !! THIS IS THE EXTRA COMMAND !! post1.comments &lt;&lt; comment2 # Note that both Comments are associated with both Post objects even # though I never explicitly associated it with post2. post1.comment_ids # =&gt; [14, 15] post2.comment_ids # =&gt; [14] </code></pre> <p>Note that there is only <strong>one</strong> comment associated with <code>post2</code> in this scenario whereas in Scenario 1 there were two. </p> <p>The Big Question: Why would running <code>post2.comments</code> before adding the new <code>Comment</code> to <code>post1</code> make any difference to which Comments were associated with <code>post2</code>? </p>
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