til/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.

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.

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.

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