How to create a new not null column with existing data?

Question

I am creating a new column in a table which is a uuid/guid.

add_column :users, :uuid, :string, null: false

I am setting the uuid using:

SecureRandom.uuid

The migration fails because the existing data doesn't have any value.

How can I set the value for each user with a new uuid during this migration?

You have neglected to mention what database software you are using....MySQL? MS SQL? PostGre? — Matt Runion
– Matt Runion, Commented Oct 1, 2018 at 0:23

Marcin Kołodziej · Accepted Answer · 2018-10-01 00:35:49Z

2

You have 2 options when adding a not null column:

Depending on what DB you're using it might or might not allow you to set an expression as the default value.

Since you've mentioned you're using Postgres, you can read more here Rails syntax for providing the default will be

default: -> { 'uuid_generate_v1()' }

answered Oct 1, 2018 at 0:25

Marcin Kołodziej

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