How to store and compare :symbols in an ActiveRecord (Ruby on Rails)

Question

I thought it would be good to populate a status field in an activeRecord table using constants. However, when it comes to checking if this status has a particular status, I\'m h

Answer 1

If I remember well symbols in ActiveRecord are stored in yaml format, some kind of conversion must be done because there is no such thing as a symbol in relational db (which I'm aware of, at least). When you read it it's then a string which will not match your symbol and not even the string of the symbol, in fact it should be something like:

:x # => "--- :x\n"

I think this plugin can solve your problem, but I haven't used it honestly. https://github.com/zargony/activerecord_symbolize

* EDIT *

I leave the above because I remember that was the situation I had and I can be corrected if I'm wrong, nonetheless I'm trying this right now and the stored value (Rails 3.1.3) is a simple string with the value of the symbol, so the following should be enough.

class Example < ActiveRecord::Base

  def aaa
    super.to_sym
  end

  def aaa=(value)
    super(value.to_sym)
    aaa
  end

end

This of course will force the value to always be a symbol

** EDIT AFTER AGES ** I think it's fine in this situation as it's clear that in the db it's a string and the logic is simple, but I strongly discourage overriding db attribute methods to add more complex logic.

Answer 2

At the request of ecoologic, here is my comment as an answer:

ecoologic has a good solution for you, but I would recommend steering away from this and making a class with constants in it. That you can do things like e.status = Statuses::CANCELLED. And internally that could be a string and it doesn't matter. You're still using constants, and it will error out if that constant doesn't exist, and it's cleaner that way.

Answer 3

Also you can overwrite the reader method:

def status
  read_attribute(:status).to_sym
end

Answer 4

As of Rails 4.1, Active Record now supports enums

From the release notes:

2.5 Active Record enums

Declare an enum attribute where the values map to integers in the database, but can be queried by name.

class Conversation < ActiveRecord::Base
  enum status: [ :active, :archived ]
end

conversation.archived!
conversation.active? # => false
conversation.status  # => "archived"

Conversation.archived # => Relation for all archived Conversations

Conversation.statuses # => { "active" => 0, "archived" => 1 }

Additional documentation here: http://api.rubyonrails.org/v4.1.0/classes/ActiveRecord/Enum.html

Answer 5

With Rails 4.1.0, you'd probably want to use Active Record enums.

To quote the official release notes:

class Conversation < ActiveRecord::Base
  enum status: [ :active, :archived ]
end
 
conversation.archived!
conversation.active? # => false
conversation.status  # => "archived"
 
Conversation.archived # => Relation for all archived Conversations
 
Conversation.statuses # => { "active" => 0, "archived" => 1 }

Answer 6

From Programming Ruby 1.9, regarding the == operator in the Symbol class (p. 729):

Returns true only if sym and obj are symbols with the same object_id.

Whatever you have stored in the DB will always have different object_id than the fixed object_id of the symbol (a pointer to a string literal, in this case).