def column_type(col_name)
      cache = Cache.instance
      cache.klass_hash[@_klass_str] ||= {}
      if v = cache.klass_hash[@_klass_str][col_name.to_s]
        cache.hit += 1
        v
      else
        cache.miss += 1
        col = @_klass_str.constantize.columns.find{|c|
          c.name == col_name.to_s
        }
        if col
          cache.klass_hash[@_klass_str][col_name.to_s] = col.type
        end
      end
    end
def column_type(col_name)
      cache = Cache.instance
      cache.klass_hash[@_klass_str] ||= {}
      if v = cache.klass_hash[@_klass_str][col_name.to_s]
        cache.hit += 1
        v
      else
        cache.miss += 1
        col = @_klass_str.constantize.columns.find{|c|
          c.name == col_name.to_s
        }
        if col
          cache.klass_hash[@_klass_str][col_name.to_s] = col.type
        end
      end
    end
cache column type