MONGOID-5158 - BSON::ObjectId#as_json and #to_json should serialize as a String without "$oid"

docs/release-notes/mongoid-7.4.txt

@@ -18,6 +18,40 @@ please consult GitHub releases for detailed release notes and JIRA for
 the complete list of issues fixed in each release, including bug fixes.
 
 
+BSON::ObjectId ``#as_json`` returns String
+------------------------------------------
+
+**Breaking change:** BSON::ObjectId ``#as_json`` used for JSON serialization
+now returns a String value. Note this will also affect the behavior of the ``#to_json`` method.
+
+.. code-block:: ruby
+
+  id = BSON::ObjectId("03d623ca58edf9046e207565")
+
+  id.as_json  #=> "03d623ca58edf9046e207565"
+
+  id.to_json  #=>  "\"03d623ca58edf9046e207565\""
+
+In Mongoid 7.3 and prior, this method returned a Hash with ``"$oid"`` as its key:
+
+.. code-block:: ruby
+
+  id.as_json  #=> { "$oid" => "03d623ca58edf9046e207565" }
+
+  id.to_json  #=> "{\"$oid\":\"03d623ca58edf9046e207565\"}"
+
+If you wish to preserve the legacy behavior, you may add the following
+patch when initializing your application:
+
+.. code-block:: ruby
+
+  class BSON::ObjectId
+    def as_json(options = nil)
+      { "$oid" => to_s }
+    end
+  end
+
+
 ``===`` Operator Matches Ruby Semantics
 ---------------------------------------
 

lib/mongoid/extensions.rb

@@ -2,7 +2,7 @@
 
 class BSON::ObjectId
   def as_json(options = nil)
-    { "$oid" => to_s }
+    to_s
   end
 end
 

spec/mongoid/extensions_spec.rb

@@ -10,8 +10,8 @@
       described_class.new
     end
 
-    it "returns the $oid plus string" do
-      expect(object_id.as_json).to eq("$oid" => object_id.to_s)
+    it "returns as a string" do
+      expect(object_id.as_json).to eq(object_id.to_s)
     end
   end
 end