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Dropping MultiJson in 1.0.3 broke Time serialization for apps using ActiveSupport #403
Description
Description
After upgrading from grape-entity 1.0.1 to 1.0.3, all Time fields in API responses changed format for apps using ActiveSupport:
- Before (1.0.1):
"2026-04-16T10:55:10.597Z"(ISO 8601) - After (1.0.3):
"2026-04-16 10:55:10 UTC"
This is a silent breaking change for API consumers expecting ISO 8601 timestamps.
Root cause
PR #385 replaced MultiJson.dump with JSON.dump in Entity#to_json: https://github.com/ruby-grape/grape-entity/pull/385/changes#diff-dede7a9b2a44333c10da3b7b006d011d8fddfc23ebaa64b415b5686c7798d296R561
MultiJson.dump internally calls Hash#to_json, which ActiveSupport intercepts to run as_json on all values — converting Time to ISO 8601. JSON.dump bypasses ActiveSupport entirely and serializes Time via its C extension using Time#to_s.
Reproduction
require 'json'
require 'active_support'
require 'active_support/core_ext/object/json'
require 'active_support/core_ext/time'
require 'grape_entity'
class TestEntity < Grape::Entity
expose :published_at
end
t = Time.utc(2026, 4, 16, 10, 55, 10, 597000)
obj = OpenStruct.new(published_at: t)
TestEntity.represent(obj).to_json
# grape-entity 1.0.1 => {"published_at":"2026-04-16T10:55:10.597Z"} ✅
# grape-entity 1.0.3 => {"published_at":"2026-04-16 10:55:10 UTC"} ❌Environment
- Ruby 4.0.0
- Rails 8.0.5
- grape-entity 1.0.3
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dblock commentedon Apr 16, 2026
@Morxander want to PR reverting that change?
stevenou commentedon Apr 16, 2026
related error:
numbata commentedon Apr 17, 2026
@dblock omw with reverting.
Fix Time serialization regression introduced by dropping MultiJson
Revert dropping MultiJson in favor of JSON.dump (#385)
numbata commentedon Apr 17, 2026
Thank you for the detailed report and reproduction, @Morxander. And @stevenou — good catch on the
defined?(::MultiJson)load-order race, that was an additional blind spot.Here's the rollout plan:
multijsondependency #385 and restoresMultiJson.dump, bringing serialization back to the 1.0.1 behavior. This will ship as 1.0.4 so affected apps can pin or upgrade immediately.Hash#to_jsoninstead ofJSON.dump, which goes through ActiveSupport's as_json chain. This will land in a future minor version.Both PRs include regression tests for Time serialization in flat and nested exposures to prevent this going forward.
numbata commentedon Apr 17, 2026
Reverted in 1.0.4, restoring the previous Time serialization behavior.
Closing this - proper removal of MultiJson is tracked in #404.
Fix Time serialization regression introduced by dropping MultiJson