Add default_scope note to AR guide [ci skip]

Adds note to explain unexpected behavior described in issue #28561.
Developers may be surprised that the internal representation of similar
query conditions in Hash and Array formats in default_scope will yield 
different results for model initialization.
Link: https://github.com/rails/rails/issues/28561

1 files changed, 14 insertions, 2 deletions

diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md
index 2902c5d677..26d01d4ede 100644
--- a/guides/source/active_record_querying.md
+++ b/guides/source/active_record_querying.md
@@ -1381,8 +1381,9 @@ class Client < ApplicationRecord
 end
 ```
 
-NOTE: The `default_scope` is also applied while creating/building a record.
-It is not applied while updating a record. E.g.:
+NOTE: The `default_scope` is also applied while creating/building a record
+when the scope arguments are given as a `Hash`. It is not applied while 
+updating a record. E.g.:
 
 ```ruby
 class Client < ApplicationRecord
@@ -1393,6 +1394,17 @@ Client.new          # => #<Client id: nil, active: true>
 Client.unscoped.new # => #<Client id: nil, active: nil>
 ```
 
+Be aware that, when given in the `Array` format, `default_scope` query arguments
+cannot be converted to a `Hash` for default attribute assignment. E.g.:
+
+```ruby
+class Client < ApplicationRecord
+  default_scope { where("active = ?", true) }
+end
+
+Client.new # => #<Client id: nil, active: nil>
+```
+
 ### Merging of scopes
 
 Just like `where` clauses scopes are merged using `AND` conditions.