rails--rails/activesupport/CHANGELOG.md

• Raise an error when multiple included blocks are defined for a Concern. The old behavior would silently discard previously defined blocks, running only the last one.

  Mike Dillon

• Replace multi_json with json.

  Since Rails requires Ruby 1.9 and since Ruby 1.9 includes json in the standard library, multi_json is no longer necessary.

  Erik Michaels-Ober

• Added escaping of U+2028 and U+2029 inside the json encoder. These characters are legal in JSON but break the Javascript interpreter. After escaping them, the JSON is still legal and can be parsed by Javascript.

  Mario Caropreso + Viktor Kelemen + zackham

• Fix skipping object callbacks using metadata fetched via callback chain inspection methods (_*_callbacks)

  Sean Walbran

• Add a fetch_multi method to the cache stores. The method provides an easy to use API for fetching multiple values from the cache.

  Example:

  # Calculating scores is expensive, so we only do it for posts
  # that have been updated. Cache keys are automatically extracted
  # from objects that define a #cache_key method.
  scores = Rails.cache.fetch_multi(*posts) do |post|
    calculate_score(post)
  end
  

  Daniel Schierbeck

Please check 4-0-stable for previous changes.