Add config to disable sessid column fallback

I'm working on removing queries in my application that should be going
through the SchemaCache in production but currently are not. I found
that the `sessions` table is being queried during runtime due to the
`reset_column_information` when the class is loaded (which clears the
SchemaCache for the `sessions` table).

This commit introduces a new configuration to disable the `sessid`
column fallback (which is the source of the `reset_column_information`).

Since the `session_id` -> `sessid` fallback has been in place for
[twenty years][1], there may be an argument to just remove it, but this
gem is very very stable so breaking changes should probably be held to
an even higher threshold.

[1]: rails/rails@452442d

Author: skipkayhil

lib/active_record/session_store.rb

@@ -8,6 +8,9 @@ module ActiveRecord
   module SessionStore
     autoload :Session, 'active_record/session_store/session'
 
+    @disable_sessid_fallback = false
+    singleton_class.attr_accessor :disable_sessid_fallback
+
     module ClassMethods # :nodoc:
       mattr_accessor :serializer
 

lib/active_record/session_store/session.rb

@@ -22,19 +22,19 @@ def data_column_size_limit
           @data_column_size_limit ||= columns_hash[data_column_name].limit
         end
 
-        # Hook to set up sessid compatibility.
-        def find_by_session_id(session_id)
-          SEMAPHORE.synchronize { setup_sessid_compatibility! }
-          find_by_session_id(session_id)
-        end
-
-        private
-          def session_id_column
-            'session_id'
+        if SessionStore.disable_sessid_fallback
+          def find_by_session_id(session_id)
+            where(session_id: session_id).first
+          end
+        else
+          # Hook to set up sessid compatibility.
+          def find_by_session_id(session_id)
+            SEMAPHORE.synchronize { setup_sessid_compatibility! }
+            find_by_session_id(session_id)
           end
 
           # Compatibility with tables using sessid instead of session_id.
-          def setup_sessid_compatibility!
+          private def setup_sessid_compatibility!
             # Reset column info since it may be stale.
             reset_column_information
             if columns_hash['sessid']
@@ -52,6 +52,12 @@ def self.find_by_session_id(session_id)
               end
             end
           end
+        end
+
+        private
+          def session_id_column
+            'session_id'
+          end
       end
 
       def initialize(*)

test/session_test.rb

@@ -108,6 +108,36 @@ def self.session_id_column
         Session.reset_column_information
       end
 
+      def test_find_by_sess_id_compat_disabled
+        old_fallback = ActiveRecord::SessionStore.disable_sessid_fallback
+        ActiveRecord::SessionStore.disable_sessid_fallback = true
+
+        # Force class reload, as we need to redo the meta-programming
+        ActiveRecord::SessionStore.send(:remove_const, :Session)
+        load 'active_record/session_store/session.rb'
+
+        Session.reset_column_information
+        klass = Class.new(Session) do
+          def self.session_id_column
+            'sessid'
+          end
+        end
+        klass.create_table!
+
+        assert klass.columns_hash['sessid'], 'sessid column exists'
+        session = klass.new(:data => 'hello')
+        session.sessid = "100"
+        session.save!
+
+        assert_raises(ActiveRecord::StatementInvalid) do
+          klass.find_by_session_id("100")
+        end
+      ensure
+        klass.drop_table!
+        Session.reset_column_information
+        ActiveRecord::SessionStore.disable_sessid_fallback = old_fallback
+      end
+
       def test_find_by_session_id
         Session.create_table!
         session_id = "10"