Ruby on Rails: How do I add a not null constraint to an existing column using a migration?

You can also use change_column_null:

change_column_null :table_name, :column_name, false

For Rails 4+, nates' answer (using change_column_null) is better.

Pre-Rails 4, try change_column.

1) FIRST: Add column with default value

2) THEN: Remove default value

add_column :orders, :items, :integer, null: false, default: 0
change_column :orders, :items, :integer, default: nil

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