Check If Any Records Have A Null Value

I like to add missing not null constraints where appropriate when they are missing. The change_column_null method is the Rails DSL way of doing this.

But first, you need to be sure that all databases this will be running against don't have any null values already present for any records. If there are null values present, then the migration will fail.

One way of doing that check is with some SQL and the select_values method.

ActiveRecord::Base
  .connection
  .select_values("select id from projects where user_id is null")
  .any?

This bit of SQL asks for the ids of any records in the projects table where a specific column (user_id) is explicitly null.

If this returns false, then you are good to migrate. If this returns true, then you'll have to do some data massaging first.