MONGOID-5507 - Fix two bugs in BigDecimal mongoization (#5485)

* Fix two bugs in BigDecimal mongoization
1. demongoize - has redundant elsif object.numeric?
2. mongoize - missing to_s in return condition when map_big_decimal_to_decimal128 is false

* Remove obsolete comment

* Update big_decimal.rb

* Fix spec

* MONGOID-5507 add release notes and minor changes

Co-authored-by: shields <[email protected]>
Co-authored-by: Neil Shweky <[email protected]>

Author: johnnyshields

docs/release-notes/mongoid-9.0.txt

@@ -120,3 +120,14 @@ Mongoid 9.0 flips the default of this flag from ``true`` => ``false``.
 
 This means that, by default, Mongoid 9 will update the existing document and
 will not replace it.
+
+
+Bug Fixes and Improvements
+--------------------------
+
+This section will be for smaller bug fixes and improvements:
+
+- With the ``map_big_decimal_to_decimal128`` flag set to false, ``demongoizing``
+  a non-numeric, non-string value that implements ``:to_d`` will return a string
+  rather than a ``BigDecimal``
+  `MONGOID-5507 <https://jira.mongodb.org/browse/MONGOID-5507>`_.

lib/mongoid/criteria/queryable/extensions/big_decimal.rb

@@ -31,8 +31,6 @@ def evolve(object)
                   else
                     obj.to_s
                   end
-                # Always return on string for backwards compatibility with querying
-                # string-backed BigDecimal fields.
                 when BSON::Decimal128 then obj
                 else
                   if obj.numeric?

lib/mongoid/extensions/big_decimal.rb

@@ -46,8 +46,6 @@ def demongoize(object)
           return if object.blank?
           if object.is_a?(BSON::Decimal128)
             object.to_big_decimal
-          elsif object.numeric?
-            BigDecimal(object.to_s)
           elsif object.numeric?
             object.to_d
           end
@@ -79,7 +77,7 @@ def mongoize(object)
             if object.is_a?(BSON::Decimal128) || object.numeric?
               object.to_s
             elsif !object.is_a?(String)
-              object.try(:to_d)
+              object.try(:to_d)&.to_s
             end
           end
         end

spec/mongoid/extensions/big_decimal_spec.rb

@@ -283,8 +283,8 @@
           expect(value).to be_a(ActiveSupport::Duration)
         end
 
-        it "returns nil" do
-          expect(mongoized).to eq(7200)
+        it "returns the casted value as a string" do
+          expect(mongoized).to eq("7200.0")
         end
       end