Generate UUID primary keys in the database

[matthewmcgarvey]

Fixes #122

When a user creates a migration that uses a UUID primary key, the migration will automatically set the default value to be gen_random_uuid() which comes from the pgcrypto extension. If they do not have that extension enabled, the migration will fail saying that gen_random_uuid() is an unknown function. They will need to add enable_extension "pgcrypto" in their migration before creating the table to get it working.

This does not remove or change how Avram currently sets the id value itself before inserting the record into the database

avram/src/avram/save_operation_template.cr

Lines 15 to 22 in 1e6f4ed

	{% if primary_key_type.id == UUID.id %}
	before_save set_uuid
	def set_uuid
	{% primary_key_name = type.resolve.constant("PRIMARY_KEY_NAME") %}
	{{ primary_key_name.id }}.value ||= UUID.random()
	end
	{% end %}

We will definitely need to consider how we want to make that change but it doesn't need to be considered right now since there's no harm in doing both.

[jwoertink]

Interesting. I've never used the pgcrypto before, only ever used the uuid-ossp one. Taking a look at the docs, it looks like this is supported back to PG 9.X at least, and the uuid-ossp docs actually say

Note: If you only need randomly-generated (version 4) UUIDs, consider using the gen_random_uuid() function from the pgcrypto module instead.

So I think this is great 👍

[jkthorne]

I have to do this all the time in Rails and Lucky. Thanks for this!

[matthewmcgarvey]

@jwoertink I'm not sure if I made it clear but this would be a breaking change since migrations won't work that have UUID primary keys until they enable the extension. Are you ok with this going in?

[jwoertink]

Oh, like existing migrations where people might rollback or whatever? If you happen to know a way we can catch that, or show a nice error like "You need to enable the pgcrypto extension to use UUID. Here's how: ....". If not, then I think it's fine to go in.

[matthewmcgarvey]

After looking into it, there's no simple way to add a helpful error to tell users to enable the extensions. For right now, I'm fine with the way it works. If it becomes a problem we can add it. It would be a rescue somewhere that looks for a message like function gen_random_uuid() does not exist and then wrap it. It would have to be a general rescue

[matthewmcgarvey]

Users with existing tables without the default will need to create a migration that does this for every table in the database that needs it

execute("ALTER TABLE users ALTER COLUMN id SET DEFAULT gen_random_uuid();")