Setting different default values in rails migrations?

Question

I'm trying to write a migration and it looks something like this:

class AddStatusToWorks < ActiveRecord::Migration
  def self.up
    change_table :works do |t|
        t.string :status
    end
  end

  def self.down
    change_table :works do |t|
        t.remove :status
    end
  end
end

Thing is, I want to set different default values for "status" based on a boolean value that's already in the table, "complete." If complete = true, status = "complete." If not, status = "work in progress." (The reason I want a string instead of keeping complete as the boolean is because I want there to be able to be more than two possibilites for status.) Any idea how to do that? Do I just stick an if statement in there like this

change_table :works do |t|
        t.string :status
           if (:complete == true)
               :value => "complete"
           else
               :value => "wip"
end

Er, so that doesn't look quite right. I googled a bit and found that you can set :default values, but that's not quite what I'm going for. Any ideas/help would be lovely. Thanks!

So you want to initialize status based on the current value of complete? What about new rows? — mu is too short
– mu is too short, Commented Sep 27, 2012 at 2:05
Wait! Do you mean new rows as in future entries to the database? In those cases, the user would set a value whenever they create a new work. It's just that there are a lot of entries already in the database and I'd like to know if there's an automatic way to set their values. — Matter Cat
– Matter Cat, Commented Sep 27, 2012 at 2:19
Heh, I knew I was missing something. But I caught on eventually, that counts for something, right? Looking over your other response now! — Matter Cat
– Matter Cat, Commented Sep 27, 2012 at 2:46

mu is too short · Accepted Answer · 2012-09-27 02:45:06Z

2

You don't need a default at all, you just need to add the new column and give it values. Something like this should work:

def self.up
  change_table :works do |t|
      t.string :status
  end
  Works.reset_column_information
  Works.where(:complete => true).update_all(:status => 'complete')
  Works.where(:complete => [false, nil]).update_all(:status => 'wip')
end

See the Migrations Guide for information on reset_column_information.

You could also do it straight in the database but you have to be careful about different boolean representations (PostgreSQL wants 't' and 'f', MySQL wants 1 and 0, SQLite wants 1 and 0 but Rails mistakenly uses 't' and 'f', ...):

t = connection.quote(true)
connection.execute(%Q{
  update works
  set status = case complete
    when #{t} then 'complete'
    else 'wip'
  end
})

edited Sep 27, 2012 at 2:45

answered Sep 27, 2012 at 2:36

mu is too short

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2 Comments

Matter Cat Over a year ago

So you can use "where" to pick out info, not if/else. Oh, that looks brilliant, exactly what I'm looking for. Thank you so much!

mu is too short Over a year ago

Right, you use where to tell ActiveRecord what you're looking for and then update_all to turn that into an UPDATE ... inside the database.

Luke W · Accepted Answer · 2012-09-27 01:58:19Z

0

Remember that default values are created immediately when the record is created, and thus don't yet have values for fields w/o defaults. You'll likely want to move this sort of logic to your model. Perhaps in an ActiveRecord callback, i.e. before_validation or before_save.

answered Sep 27, 2012 at 1:58

Luke W

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2 Comments

Matter Cat Over a year ago

Ahh...hmm. Okay. So basically, create the table without the if statement and then in the model, do something like this: def edit_status if self.complete = true self.status = "complete" else self.status = "wip" then before_save :edit_status Like that?

Matter Cat Over a year ago

welp, that lost a lot of the formatting. Eh. At any rate, there is not way to do it directly in the migration? Because the thing is I want the default values to be set once and then the user can directly edit them after that. If I use before_save, won't that trigger every time the user edits anything about :works?

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