Assigning default value while creating migration file

Default migration generator does not handle default values (column modifiers are supported but do not include default or null), but you could create your own generator.

You can also manually update the migration file prior to running rake db:migrate by adding the options to add_column:

add_column :tweet, :retweets_count, :integer, :null => false, :default => 0

... and read Rails API

t.integer :retweets_count, :default => 0

... should work.

See the Rails guide on migrations

Yes, I couldn't see how to use 'default' in the migration generator command either but was able to specify a default value for a new string column as follows by amending the generated migration file before applying "rake db:migrate":

class AddColumnToWidgets < ActiveRecord::Migration
  def change
    add_column :widgets, :colour, :string, default: 'red'
  end
end

This adds a new column called 'colour' to my 'Widget' model and sets the default 'colour' of new widgets to 'red'.

I tried t.boolean :active, :default => 1 in migration file for creating entire table. After ran that migration when i checked in db it made as null. Even though i told default as "1". After that slightly i changed migration file like this then it worked for me for setting default value on create table migration file.

t.boolean :active, :null => false,:default =>1. Worked for me.

My Rails framework version is 4.0.0

You would have to first create your migration for the model basics then you create another migration to modify your previous using the change_column ...

def change
    change_column :widgets, :colour, :string, default: 'red'
end