November 16, 2007

Some issues with Oracle views as ActiveRecord source

Posted by Raimonds Simanovskis • Tags: ruby, rails, oracleShow comments

I am using Ruby on Rails to publish data from existing “legacy” application on Oracle database which already have existing complex data model. I am defining additional database views on existing legacy data to which I grant select rights to Rails schema. And I am using Rails conventions when defining these views – view names as pluralized / underscored version of Rails model name, ID column as primary key and %_ID columns as foreign keys.

Typically this works quite well and I can use Rails find methods to automatically generate SQL SELECTs from these views. But for some legacy data I got the problem with Oracle number type mapping to Ruby integer type.

Rails standard convention for database NUMBER type mapping is the following:

  • NUMBER with specified scale and without precision (e.g. NUMBER) is mapped to :integer
  • NUMBER with specified scale and with precision (e.g. NUMBER) is mapped to :decimal
  • NUMBER without scale and precision (just NUMBER) is mapped to :decimal

If primary keys and foreign keys in legacy tables are defined as e.g. NUMBER then everything is OK and they will be mapped to :integer in Rails. But if primary keys or foreign keys in legacy tables are defined as NUMBER then they will be mappec to :decimal in Rails.

And what happens if e.g. primary key is mapped to :decimal in Rails? Then, for example, you get that customer.id is equal to “123.0” and you get ugly URLs like “/customers/123.0”.

One workaround is to use customer.id.to_i everywhere but it is quite annoying. Therefore I created patch for Oracle adapter (this is tested with Rails 1.2.3) which always sets data type as :integer for all primary keys (column name ID) and foreign keys (column name like %_ID). This includes also date columns patch that I wrote about previously.

module ActiveRecord::ConnectionAdapters
  class OracleColumn
    def simplified_type(field_type)
      return :boolean if OracleAdapter.emulate_booleans && field_type == 'NUMBER(1)'
      case self.name
        # RSI: treat columns which end with 'date' as ruby date columns
        when /date$/i then :date
        # RSI: removed 'date' from regex
        when /time/i then :datetime
        # RSI: treat id columns (primary key) as integer
        when /^id$/i then :integer
        # RSI: treat _id columns (foreign key) as integer
        when /_id$/i then :integer
        else super

  # RSI: patch to change selected results NUMBER to integer for primary and foreign keys
  class OracleAdapter
    def select(sql, name = nil)
      cursor = execute(sql, name)
      cols = cursor.get_col_names.map { |x| oracle_downcase(x) }
      rows = []

      while row = cursor.fetch
        hash = Hash.new

        cols.each_with_index do |col, i|
          hash[col] =
            case row[i]
            when OCI8::LOB
              name == 'Writable Large Object' ? row[i]: row[i].read
            when OraDate
              (row[i].hour == 0 and row[i].minute == 0 and row[i].second == 0) ?
              row[i].to_date : row[i].to_time
            else row[i]
            end unless col == 'raw_rnum_'
          # RSI: patch - convert to integer if column is ID or ends with _ID
          hash[col] = hash[col].to_i if (col =~ /^id$/i || col =~ /_id$/i) && hash[col]

        rows << hash

      cursor.close if cursor

I have not yet verified this with Rails 2.0. And probably I will collect all my Oracle adapter patches and will release it as plugin. Is anybody interested in this?

Fork me on GitHub