Merge pull request #35350 from kamipo/deprecate_validate_uniqueness_mismatched_collation

Deprecate mismatched collation comparison for uniquness validator

3 files changed, 16 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index f205d77ddb..823efee301 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -506,7 +506,7 @@ module ActiveRecord
         @connection
       end
 
-      def default_uniqueness_comparison(attribute, value) # :nodoc:
+      def default_uniqueness_comparison(attribute, value, klass) # :nodoc:
         case_sensitive_comparison(attribute, value)
       end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 37506a97e2..96f902792e 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -453,6 +453,20 @@ module ActiveRecord
         SQL
       end
 
+      def default_uniqueness_comparison(attribute, value, klass) # :nodoc:
+        column = column_for_attribute(attribute)
+
+        if column.collation && !column.case_sensitive?
+          ActiveSupport::Deprecation.warn(<<~MSG.squish)
+            Uniqueness validator will no longer enforce case sensitive comparison in Rails 6.1.
+            To continue case sensitive comparison on the :#{attribute.name} attribute in #{klass} model,
+            pass `case_sensitive: true` option explicitly to the uniqueness validator.
+          MSG
+        end
+
+        super
+      end
+
       def case_sensitive_comparison(attribute, value) # :nodoc:
         column = column_for_attribute(attribute)
 
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 88ae62c681..dc1be73a60 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -63,7 +63,7 @@ module ActiveRecord
           if bind.nil?
             attr.eq(bind)
           elsif !options.key?(:case_sensitive)
-            klass.connection.default_uniqueness_comparison(attr, bind)
+            klass.connection.default_uniqueness_comparison(attr, bind, klass)
           elsif options[:case_sensitive]
             klass.connection.case_sensitive_comparison(attr, bind)
           else