Fixes rails#41521, ActiveModel::Dirty fails on to_json

Author: anilmaurya

activemodel/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Fix `to_json` for `ActiveModel::Dirty` object.
+    
+    Exclude +mutations_from_database+ attribute from json as it lead to recursion.
+
+    *Anil Maurya*
+
 *   Add `ActiveModel::AttributeSet#values_for_database`
 
     Returns attributes with values for assignment to the database.

activemodel/lib/active_model/dirty.rb

@@ -140,6 +140,11 @@ def initialize_dup(other) # :nodoc:
       @mutations_from_database = nil
     end
 
+    def as_json(options = {}) # :nodoc:
+      options[:except] = [options[:except], "mutations_from_database"].flatten
+      super(options)
+    end
+
     # Clears dirty data and moves +changes+ to +previous_changes+ and
     # +mutations_from_database+ to +mutations_before_last_save+ respectively.
     def changes_applied

activemodel/test/cases/dirty_test.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "cases/helper"
+require "active_support/json"
 
 class DirtyTest < ActiveModel::TestCase
   class DirtyModel
@@ -237,4 +238,19 @@ def save
   test "model can be dup-ed without Attributes" do
     assert @model.dup
   end
+
+  test "to_json should work on model" do
+    @model.name = "Dmitry"
+    assert_equal "{\"name\":\"Dmitry\",\"color\":null,\"size\":null,\"status\":\"initialized\"}", @model.to_json
+  end
+
+  test "to_json should work on model with :except string option " do
+    @model.name = "Dmitry"
+    assert_equal "{\"color\":null,\"size\":null,\"status\":\"initialized\"}", @model.to_json(except: "name")
+  end
+
+  test "to_json should work on model with :except array option " do
+    @model.name = "Dmitry"
+    assert_equal "{\"color\":null,\"size\":null,\"status\":\"initialized\"}", @model.to_json(except: ["name"])
+  end
 end