Initialise new fields in existing entities with the default value

[snigdha920]

Description

I have an entity schema which was used to create many entities in the database. Now, I'm updating the entity schema to add a new embeddable field.

When fetching an existing entity, the value of the new field is undefined which is normal because the field did not exist when the entity was created.

However I want this field to be initialised with a default value, even for the entities which were created in the database before this field was added.

I thought just setting the default field on the properties in the embeddable would achieve this, but it doesn't.

This is also understandable, since:

• we want to reflect the true state of the database.
• the field is only used while creating an entity, but not while fetching it

The field I want to add is a mandatory field, but the entities in the database just return undefined for that field. Since it is a mandatory field, the undefined isn't caught at compile time, and I get runtime errors.

Here is the reproduction repo: https://github.com/snigdha920/nestjs-mikro-embeddables

Proposal

So I propose: we add an option like valueForExisting (just a placeholder name) in the @Embeddable / @Propery decorators to explicitly set the fields with the value given for existing entities.

It could mean a write transaction to the database when only a read transaction is expected, which is an anti-pattern, but I'm not sure what can be done about it?

How does the idea seem? Is there a different way you propose I handle this? Happy to hear thoughts and provide more info!

[snigdha920]

This is the perfect case for a DB migration, didn't cross my mind.