ray_apps_blog

mix.oracle.com team created opportunity to suggest and vote for sessions at Oracle OpenWorld conference. Therefore I will also try this opportunity and will suggest topic which is covered by many posts in this blog - I proposed session Using Ruby on Rails with Oracle E-Business Suite.

So if you would like me to present this topic in Oracle OpenWorld conference then please go to mix.oracle.com and vote for it!

When using Ruby on Rails on Oracle I noticed that my database migration tasks are much slower than on MySQL.

I just found the cause for that - rake db:schema:dump task was taking very long time on my Oracle databases (and this task is executed at the end of rake db:migrate). As a result of this task Oracle Rails adapter is executing

SELECT LOWER(table_name) FROM user_tables

statement. If your database contains a lot of other schemas with a lot of tables (as in my case I deploy Rails user schema in Oracle E-Business Suite database) then this statement is quite slow (it took more than 10 seconds in my case).

As all Rails tables are located in Rails user schema then you can get the same result with

SELECT LOWER(table_name) FROM all_tables WHERE owner = SYS_CONTEXT('userenv','session_user')

which now executes much faster than original statement.

So you can make the following patch for Oracle Rails adapter to make this change

module ActiveRecord
  module ConnectionAdapters
    class OracleAdapter
      def tables(name = nil)
        select_all("select lower(table_name) from all_tables where owner = sys_context('userenv','session_user')").inject([]) do | tabs, t |
          tabs << t.to_a.first.last
        end
      end
    end
  end
end

and include it in environment.rb file or in some separate patch file which you load at Rails startup.

P.S. I have published all my patches for Oracle Rails 2.0 adapter. You can download this file, place it in Rails application lib directory and then just include

require "oracle_adapter_20_patch"

in your environment.rb file. Look at comments in this file to find out what each patch is doing.

As I started to explore Rails 2.0 I tried to migrate one application to Rails 2.0 which is using Oracle as a database. Here are some initial tips for Rails 2.0 on Oracle that I found out.

Oracle adapter is no more included in Rails 2.0 so you need to install it separately. It is also not yet placed on gems.rubyforge.org therefore you need to install it with:

sudo gem install activerecord-oracle-adapter --source http://gems.rubyonrails.org

The next issue that you will get is error message “select_rows is an abstract method”. You can find more information about it in this ticket. As suggested I fixed this issue with the following Oracle adapter patch that I call from anvironment.rb file:

module ActiveRecord
  module ConnectionAdapters
    class OracleAdapter
      def select_rows(sql, name = nil)
        result = select(sql, name)
        result.map{ |v| v.values}
      end
    end
  end
end

And then I faced very strange behaviour that my Rails application was not working with database session store - no session data was saved. When I changed session store to cookies then everything worked fine.

When I continued investigation I found out that the issue was that for each new session new row was created in “sessions” table but no session data was saved in “data” column. As “data” column is text field which translates to CLOB data type in Oracle then it is not changed in Oracle adapter by INSERT or UPDATE statements but with special “write_lobs” after_save callback (this is done so because in Oracle there is limitation that literal constants in SQL statements cannot exceed 4000 characters and therefore such hack with after_save callback is necessary). And then I found that class CGI::Session::ActiveRecordStore::Session (which is responsible for database session store) does not have this write_lobs after_save filter. Why so?

As I understand now in Rails 2.0 ActiveRecord class definition sequence has changed - now at first CGI::Session::ActiveRecordStore::Session class is defined which inherits from ActiveRecord::Base and only afterwards OracleAdapter is loaded which adds write_lobs callback to ActiveRecord::Base but at this point it is not adding this callback to already defined Session class. As in Rails 1.2 OracleAdapter was loaded together with ActiveRecord and before Session class definition then there was no such issue.

So currently I solved this issue with simple patch in environment.rb file:

class CGI::Session::ActiveRecordStore::Session
  after_save :write_lobs
end

Of course it would be nicer to force that OracleAdapter is loaded before CGI::Session::ActiveRecordStore::Session definition (when ActionPack is loaded). If somebody knows how to do that please write a comment :)