Move while_preventing_writes from conn to handler

If we put the `while_preventing_writes` on the connection then the
middleware that sends reads to the primary and ensures they can't write
will not work. The `while_preventing_writes` will only be applied to the
connection which it's called on - which in the case of the middleware is
Ar::Base.

This worked fine if you called it directly like
`OtherDbConn.connection.while_preventing_writes` but Rails didn't have a
way of knowing you wanted to call it on all the connections.

The change here moves the `while_preventing_writes` method from the
connection to the handler so that it can block writes to all queries for
that handler. This will apply to all the connections associated with
that handler.

1 files changed, 2 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/middleware/database_selector/resolver.rb b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
index 5b89c8f668..3eb1039c50 100644
--- a/activerecord/lib/active_record/middleware/database_selector/resolver.rb
+++ b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
@@ -45,8 +45,8 @@ module ActiveRecord
 
         private
           def read_from_primary(&blk)
-            ActiveRecord::Base.connection.while_preventing_writes do
-              ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
+              ActiveRecord::Base.connection_handler.while_preventing_writes do
                 instrumenter.instrument("database_selector.active_record.read_from_primary") do
                   yield
                 end