CODEWITHSUNDEEP
ruby-on-railsrubymigration
Jon
Jon

Reputation: 3985

Add a default value to a column through a migration

How do I add a default value to a column that already exists through a migration?

All the documentation I can find shows you how to do it if the column doesn't already exist but in this case it does.

Upvotes: 323

Views: 241442

Answers (8)

Miguel Peniche
Miguel Peniche

Reputation: 1032

Answer from @gazza is correct, although I would suggest you indicate the from and to so you can make it reversible:

change_column :users, :admin, :boolean, from: true, to: false

Upvotes: 1

rookieRailer
rookieRailer

Reputation: 2341

This is what you can do:

class Profile < ActiveRecord::Base
  before_save :set_default_val

  def set_default_val
    self.send_updates = 'val' unless self.send_updates
  end
end

EDIT: ...but apparently this is a Rookie mistake!

Upvotes: -62

csi
csi

Reputation: 9338

For Rails 4+, use change_column_default

def change
  change_column_default :table, :column, value
end

Upvotes: 151

Gazza
Gazza

Reputation: 3141

change_column_default :employees, :foreign, false

Upvotes: 213

Praveen George
Praveen George

Reputation: 9725

**Rails 4.X +**

As of Rails 4 you can't generate a migration to add a column to a table with a default value, The following steps add a new column to an existing table with default value true or false.

1. Run the migration from command line to add the new column

$ rails generate migration add_columnname_to_tablename columnname:boolean

The above command will add a new column in your table.

2. Set the new column value to TRUE/FALSE by editing the new migration file created.

class AddColumnnameToTablename < ActiveRecord::Migration
  def change
    add_column :table_name, :column_name, :boolean, default: false
  end
end

**3. To make the changes into your application database table, run the following command in terminal**

$ rake db:migrate

Upvotes: 53

bfcoder
bfcoder

Reputation: 3132

Using def change means you should write migrations that are reversible. And change_column is not reversible. You can go up but you cannot go down, since change_column is irreversible.

Instead, though it may be a couple extra lines, you should use def up and def down

So if you have a column with no default value, then you should do this to add a default value.

def up
  change_column :users, :admin, :boolean, default: false
end

def down
  change_column :users, :admin, :boolean, default: nil
end

Or if you want to change the default value for an existing column.

def up
  change_column :users, :admin, :boolean, default: false
end

def down
  change_column :users, :admin, :boolean, default: true
end

Upvotes: 63

Maur&#237;cio Linhares
Maur&#237;cio Linhares

Reputation: 40333

Here's how you should do it:

change_column :users, :admin, :boolean, :default => false

But some databases, like PostgreSQL, will not update the field for rows previously created, so make sure you update the field manaully on the migration too.

Upvotes: 408

axeltaglia
axeltaglia

Reputation: 2593

Execute:

rails generate migration add_column_to_table column:boolean

It will generate this migration:

class AddColumnToTable < ActiveRecord::Migration
  def change
    add_column :table, :column, :boolean
  end
end

Set the default value adding :default => 1

add_column :table, :column, :boolean, :default => 1

Run:

rake db:migrate

Upvotes: 11

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