Setting default integer values in activerecord

Question

So I'm trying to set a the default value of a 'votes' column to 0, but when I create instances of answers in rails c or through unit tests, the votes value is always nil. Any ideas on why this isn't working?

I've changed the migration like so:

class AddVotesToAnswers < ActiveRecord::Migration
  def change
    add_column :answers, :votes, :integer, default: 0
  end
end

Here's the model:

class Answer < ActiveRecord::Base
  attr_accessible :is_correct, :question_id, :title, :sms_answer_code, :votes

  belongs_to :question

  def upvote
    self.votes += 1
  end

end

Test Spec

require 'spec_helper'

describe Answer do
  before do
    @answer = Answer.make!
  end

  it "should have a default vote value of zero" do
    binding.pry
    @answer.votes.should eq(0)
  end

end

Could be 1 of 2 things: 1) you need to run rake db:test:prepare to get the default value in your test database. 2) you edited the default value in your migration after running it and should rake db:migrate:redo — Jesse Wolgamott
– Jesse Wolgamott, Commented Jun 10, 2013 at 2:38

zeantsoi · Accepted Answer · 2013-06-10 02:53:37Z

9

The default for a DB migration must be set at the time at which you run the migration – adding a default value once a table has been created won't work.

If your DB is already seeded (and you don't want to change the schema), the following hook in ActiveRecord will do the job:

class Answer < ActiveRecord::Base
    attr_accessible :is_correct, :question_id, :title, :sms_answer_code, :votes

    belongs_to :question

    before_save :default_vote_count

    def upvote
        self.votes += 1
    end

    def default_vote_count
        self.votes ||= 0
    end
end

EDIT:

If you want to change the actual default value in the DB, you can create a change migration containing the following:

# in console
rails g migration change_default_for_answer_votes

# in migration file
class ChangeDefaultForAnswerVotes < ActiveRecord::Migration

  def change
    change_column :answers, :votes, :integer, :default => 0
  end

end

Some databases (Postgres, for instance) don't automatically assign newly updated default values to existing column entries, so you'll need to iterate through existing answers to manually update each to the default votes count:

# in console
Answer.update_all(votes: 0)

edited Jun 10, 2013 at 2:53

answered Jun 10, 2013 at 2:25

zeantsoi

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1 Comment

Keith Johnson Over a year ago

Although I guess you're not supposed to change the schema, it seems like it'd be thinner.

MERM · Accepted Answer · 2013-06-10 02:15:46Z

1

You need to say that as: add_column :answers, :votes, :integer, :default => 0

answered Jun 10, 2013 at 2:15

MERM

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3 Comments

Keith Johnson Over a year ago

That's how I had it at first but it didn't work. Here's the error from the unit test: ' # ./spec/models/answer_spec.rb:10:in `block (2 levels) in <top (required)>'

MERM Over a year ago

That is the syntax for the migration. You might have an issue in your spec. Why don't you post it

Keith Johnson Over a year ago

Just added it. I don't think thats the issue though because if I manually instantiate the model in the console, 'votes' still defaults to nil. Also, thanks for tips!

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