Add a default value to a column through a migration

Question

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 alr

Answer 1

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