1 files changed, 13 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index db5e7b82ca..ba053700f2 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -80,11 +80,11 @@ module ActiveRecord
       class_attribute :default_connection_handler, instance_writer: false
 
       def self.connection_handler
-        Thread.current[:active_record_connection_handler] || self.default_connection_handler
+        ActiveRecord::RuntimeRegistry.connection_handler || default_connection_handler
       end
 
       def self.connection_handler=(handler)
-        Thread.current[:active_record_connection_handler] = handler
+        ActiveRecord::RuntimeRegistry.connection_handler = handler
       end
 
       self.default_connection_handler = ConnectionAdapters::ConnectionHandler.new
@@ -307,9 +307,11 @@ module ActiveRecord
       id.hash
     end
 
-    # Freeze the attributes hash such that associations are still accessible, even on destroyed records.
+    # Clone and freeze the attributes hash such that associations are still
+    # accessible, even on destroyed records, but cloned models will not be
+    # frozen.
     def freeze
-      @attributes.freeze
+      @attributes = @attributes.clone.freeze
       self
     end
 
@@ -344,9 +346,15 @@ module ActiveRecord
       self.class.connection
     end
 
+    def connection_handler
+      self.class.connection_handler
+    end
+
     # Returns the contents of the record as a nicely formatted string.
     def inspect
-      inspection = if @attributes
+      # We check defined?(@attributes) not to issue warnings if the object is
+      # allocated but not initialized.
+      inspection = if defined?(@attributes) && @attributes
                      self.class.column_names.collect { |name|
                        if has_attribute?(name)
                          "#{name}: #{attribute_for_inspect(name)}"