Restrict the columns represented in ActiveRecord

问题

How to change ActiveRecord so that it always has a restricted set of columns. I dont want all the columns in the backened table to present in the Model. This unnecessarily bloats the ActiveRecord's memory footprint as well as the time taken to query the record.

There are attributes like select (ar.rubyonrails.org/classes/ActiveRecord/Base) which can be used to SELECT only few columns. But is there any way we can force ActiveRecord to never query those columns inspite of the user performing just find without specifying :select all the time.

回答1:

use default_scope

e.g.

class MyModel < ActiveRecord::Base
  default_scope select("column1, column2, column3")

  ...
end

回答2:

Can't you do with a scope:

IGNORED = %w( id created_at updated_at )
scope :filtered, lambda { select( cols ) }

def self.cols
  attribute_names = []
  attributes = self.columns.reject { |c| IGNORED.include?( c.name ) }

  attributes.each { |attr| attribute_names << attr.name }
  attribute_names
end

Model.filtered
[#<Model name: "Test 2", reg_num: "KA 02", description: "aldsfjadflkj">] 

来源：https://stackoverflow.com/questions/8758455/restrict-the-columns-represented-in-activerecord