Query to define a default value in a database migration

Question

In this SO article I can see how to add a default value to a certain table:

Add a default value to a column through a migration

change_column :shops, :currency_id, :integer, :default => 1

I have another table currencies that has an ID and also a ISO_Name. I want the system to use EUR as default value. But it's possible that this has ID 5 or ID 1 or ...

So my question: How can I define a default value that is based on the result of a query? For example Currency.find_by_iso_code('EUR').id

if you have the field as iso_name, then why you are using iso_code. It can be done that you have mentioned change_column :shops, :currency_id, :integer, :default => Currency.find_by_iso_name('EUR').id — Bachan Smruty, Jun 27 '13 at 09:11
You are absolutely right, it's as easy as that! Currency.find_by_iso_name('EUR').id works. If you add this as I'll mark as answer. — rept, Jun 27 '13 at 15:30
good to know that it worked. By the way I have added it as answer :) — Bachan Smruty, Jun 27 '13 at 15:48

score 1 · Accepted Answer · answered Jun 27 '13 at 15:43

1

As you have iso_name field in the currencies, you can achieve it by the following code.

change_column :shops, :currency_id, :integer, :default => Currency.find_by_iso_name('EUR').id

answered Jun 27 '13 at 15:43

Bachan Smruty

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score 0 · Answer 2 · answered Jun 27 '13 at 08:42

0

How about:

class SetDefaultCurrencyForShops < ActiveRecord::Migration
  def up
    currency = Currency.find_by_iso_code('EUR')
    if currency
      change_column :shops, :currency_id, :integer, :default => currency.id
    end
  end
end

answered Jun 27 '13 at 08:42

Ju Liu

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13
18

Query to define a default value in a database migration

2 Answers2