> For the complete documentation index, see [llms.txt](https://ploegert.gitbook.io/til/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ploegert.gitbook.io/til/programmy/rails/write-reversible-migration-to-set-default.md).

# Write Reversible Migration To Set Default

You can use the `change_column_default` method to alter the default value of a column. If the column doesn't have a default, then you'd essentially be changing the default from `nil` to *some value*.

```ruby
def up
  change_column_default :books, :published, false
end

def down
  change_column_default :books, :published, nil
end
```

This is fine, but you can write the migration as a single, reversible `change` method using the `:from` and `:to` options.

```ruby
def change
  change_column_default :books, :published, from: nil, to: false
end
```

When you migrate, the default will be set to `false`. When you rollback, the default will be removed.

[source](https://blog.arkency.com/how-to-add-a-default-value-to-an-existing-column-in-a-rails-migration/)