Rails migrations: Undo default setting for a column

Question

Rails 5+

def change
  change_column_default( :table_name, :column_name, from: nil, to: false )
end

Rails 3 and Rails 4

def up
  change_column_default( :table_name, :column_name, nil )
end

def down
  change_column_default( :table_name, :column_name, false )
end

Sounds like you're doing the right thing with your 'execute', as the docs point out:

change_column_default(table_name, column_name, default)

Sets a new default value for a column. If you want to set the default value to NULL, you are out of luck. You need to DatabaseStatements#execute the appropriate SQL statement yourself. Examples

change_column_default(:suppliers, :qualification, 'new')
change_column_default(:accounts, :authorized, 1)

The following snippet I use to make NULL columns NOT NULL, but skip DEFAULT at schema level:

def self.up
  change_column :table, :column, :string, :null => false, :default => ""
  change_column_default(:table, :column, nil)
end