instance method find_one

# File activerecord/lib/active_record/relation/finder_methods.rb, line 317
    def find_one(id)
      id = id.id if ActiveRecord::Base === id

      if IdentityMap.enabled? && where_values.blank? &&
        limit_value.blank? && order_values.blank? &&
        includes_values.blank? && preload_values.blank? &&
        readonly_value.nil? && joins_values.blank? &&
        !@klass.locking_enabled? &&
        record = IdentityMap.get(@klass, id)
        return record
      end

      column = columns_hash[primary_key]

      substitute = connection.substitute_at(column, @bind_values.length)
      relation = where(table[primary_key].eq(substitute))
      relation.bind_values = [[column, id]]
      record = relation.first

      unless record
        conditions = arel.where_sql
        conditions = " [#{conditions}]" if conditions
        raise RecordNotFound, "Couldn't find #{@klass.name} with #{primary_key}=#{id}#{conditions}"
      end

      record
    end