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#4637 ✓stale
Sam Pohlenz

[PATCH] Fix JSON serialization of ActiveModel::Errors

Reported by Sam Pohlenz | May 18th, 2010 @ 08:48 AM

JSON encoding an ActiveModel::Errors object with :only option currently breaks:

>> ActiveSupport::JSON.encode(, :only => :attribute)
ArgumentError: wrong number of arguments (0 for 1)
from /Users/sam/Development/rails/activesupport/lib/active_support/core_ext/hash/slice.rb:17:in `initialize'
from /Users/sam/Development/rails/activesupport/lib/active_support/core_ext/hash/slice.rb:17:in `new'
from /Users/sam/Development/rails/activesupport/lib/active_support/core_ext/hash/slice.rb:17:in `slice'
from /Users/sam/Development/rails/activesupport/lib/active_support/json/encoding.rb:210:in `as_json'
from /Users/sam/Development/rails/activesupport/lib/active_support/json/encoding.rb:48:in `encode'
from /Users/sam/Development/rails/activesupport/lib/active_support/json/encoding.rb:62:in `check_for_circular_references'
from /Users/sam/Development/rails/activesupport/lib/active_support/json/encoding.rb:47:in `encode'
from /Users/sam/Development/rails/activesupport/lib/active_support/json/encoding.rb:32:in `encode'
from (irb):2

This fails as Hash#slice in ActiveSupport tries to instantiate a new ActiveModel::Errors with no arguments (one arg is required).

This patch changes the behavior of Hash#slice to dup and clear the hash, which will work even when hash subclasses change the #initialize parameters.

Comments and changes to this ticket

  • Rizwan Reza

    Rizwan Reza May 21st, 2010 @ 12:50 AM

    • no changes were found...
  • Étienne Barrié

    Étienne Barrié May 21st, 2010 @ 01:46 PM

    What's strange in the patch is that the test is in activemodel while the code change is in activesupport. The change also implies that now all slice operations will first dup the hash before clearing it, which might be a performance problem, but I have no data to back that. You might want to just override slice in ActiveModel::Errors if you just want it to be serializable. Or maybe just use in slice.

    I attached a patch with a test related to the change in activesupport anyway.

  • Santiago Pastorino

    Santiago Pastorino February 2nd, 2011 @ 04:38 PM

    • State changed from “new” to “open”

    This issue has been automatically marked as stale because it has not been commented on for at least three months.

    The resources of the Rails core team are limited, and so we are asking for your help. If you can still reproduce this error on the 3-0-stable branch or on master, please reply with all of the information you have about it and add "[state:open]" to your comment. This will reopen the ticket for review. Likewise, if you feel that this is a very important feature for Rails to include, please reply with your explanation so we can consider it.

    Thank you for all your contributions, and we hope you will understand this step to focus our efforts where they are most helpful.

  • Santiago Pastorino

    Santiago Pastorino February 2nd, 2011 @ 04:38 PM

    • State changed from “open” to “stale”

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