Tutorial :How to apply this filter in Rails


I have a table called as language which has a column called as lang_code. It has the following values.

id  lang_code  created_at           updated_at  1   ARA        2010-07-29 15:27:25  NULL  2   CHI        2010-07-29 15:27:25  NULL  3   DAN        2010-07-29 15:27:25  NULL  4   DEU        2010-07-29 15:27:25  NULL  5   ESP        2010-07-29 15:27:25  NULL  6   KOR        2010-07-29 15:27:25  NULL  7   VIE        2010-07-29 15:27:25  NULL  

I have a requirement to remove 3 languages (CHI, DAN ad VIE) from this table. I can simply write a migration and remove the values permanently from the table. But I do not want to do that. Instead, I want to filter them out in the model level so that any operation that I do on this particular model should not have these three languages in it. How to do that in Rails?



Use default_scope:

class Language < ActiveRecord::Base    UNWANTED_LANGUAGES = ["CHI", "DAN", "VIE"]    default_scope :conditions => ["lang_code not in (?)", UNWANTED_LANGUAGES]    ...  end  


  1. You create a migration where you add an :active column. You set a default (EG default is active)

  2. In the same migration(be carefull to call Language.reset_column_information) or in another migration, you take care of any DB relations with (CHI, DAN, VIE) involved. Then, you inactivate them (inactive = true)

  3. In the Language class, you use a default_scope:

    default_scope :conditions => { :active => true }

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