Partial revert the changing default value of `readonly_value`

This is a partial revert of #26182. There is no reason to change the
default value.

2 files changed, 3 insertions, 15 deletions

diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 0296101f81..009624e194 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -378,7 +378,7 @@ module ActiveRecord
           if !VALID_UNSCOPING_VALUES.include?(scope)
             raise ArgumentError, "Called unscope() with invalid unscoping argument ':#{scope}'. Valid arguments are :#{VALID_UNSCOPING_VALUES.to_a.join(", :")}."
           end
-          set_value(scope, nil)
+          set_value(scope, DEFAULT_VALUES[scope])
         when Hash
           scope.each do |key, target_value|
             if key != :where
@@ -905,7 +905,7 @@ module ActiveRecord
     protected
       # Returns a relation value with a given name
       def get_value(name) # :nodoc:
-        @values[name] || default_value_for(name)
+        @values.fetch(name, DEFAULT_VALUES[name])
       end
 
       # Sets the relation value with the given name
@@ -1190,7 +1190,6 @@ module ActiveRecord
 
       DEFAULT_VALUES = {
         create_with: FROZEN_EMPTY_HASH,
-        readonly: false,
         where: Relation::WhereClause.empty,
         having: Relation::WhereClause.empty,
         from: Relation::FromClause.empty
@@ -1199,15 +1198,5 @@ module ActiveRecord
       Relation::MULTI_VALUE_METHODS.each do |value|
         DEFAULT_VALUES[value] ||= FROZEN_EMPTY_ARRAY
       end
-
-      Relation::SINGLE_VALUE_METHODS.each do |value|
-        DEFAULT_VALUES[value] = nil if DEFAULT_VALUES[value].nil?
-      end
-
-      def default_value_for(name)
-        DEFAULT_VALUES.fetch(name) do
-          raise ArgumentError, "unknown relation value #{name.inspect}"
-        end
-      end
   end
 end
diff --git a/activerecord/test/cases/relation_test.rb b/activerecord/test/cases/relation_test.rb
index b424ca91de..dbf3389774 100644
--- a/activerecord/test/cases/relation_test.rb
+++ b/activerecord/test/cases/relation_test.rb
@@ -24,10 +24,9 @@ module ActiveRecord
 
     def test_initialize_single_values
       relation = Relation.new(FakeKlass, :b, nil)
-      (Relation::SINGLE_VALUE_METHODS - [:create_with, :readonly]).each do |method|
+      (Relation::SINGLE_VALUE_METHODS - [:create_with]).each do |method|
         assert_nil relation.send("#{method}_value"), method.to_s
       end
-      assert_equal false, relation.readonly_value
       value = relation.create_with_value
       assert_equal({}, value)
       assert_predicate value, :frozen?