Required files
arel/visitors/visitor
arel/visitors/depth_first
arel/visitors/to_sql
arel/visitors/sqlite
arel/visitors/postgresql
arel/visitors/mysql
arel/visitors/mssql
arel/visitors/oracle
arel/visitors/join_sql
arel/visitors/where_sql
arel/visitors/order_clauses
arel/visitors/dot