Remove requirement to save record before adding link(s)

[lozcalver]

Description

Currently unsaved DataObjects will show “Cannot add links until the record has been saved” instead of allowing the author to add links, which is a poor editing experience

Additional context or points of discussion

No response

Validations

• You intend to implement the feature yourself
• You have read the contributing guide
• You strongly believe this feature should be in core, rather than being its own community module
• You have checked for existing issues or pull requests related to this feature (and didn't find any)

[GuySartorelli]

The decision to not allow adding links until a record is created was intentional, for two reasons:

1. We didn't want orphan link records floating around if you chose not to create the parent record
2. The Owner relation needs to be set when saving the link, which we can't do if the owner doesn't exist

Do you have thoughts about how you would resolve those problems?

[lozcalver]

We didn't want orphan link records floating around if you chose not to create the parent record

Yep that is a trade-off. In terms of database size, I’d argue the current approach is much more likely to result in unnecessary version records (save, then add link, then save again) than the new approach is likely to result in orphaned links. I suppose we could look to add some code to tidy these up – e.g. whenever you save a new link it searches for and removes any orphans that haven’t been assigned an owner in, say, 24 hours? That said, they’re not really doing any harm.

It does feel wrong to leave these lingering from a developer POV, but not as wrong as having to save an incomplete record to access the link field when authoring content. As an aside, it also means making a link field required isn’t possible with un-versioned DataObjects.

The Owner relation needs to be set when saving the link, which we can't do if the owner doesn't exist

My plan here is actually the same as my plan to fix the multi-link field (which doesn’t currently work in my POC) - add an AbstractLinkField::saveInto() method that ensures the relation is set. The link IDs are already included in the POST data, so hopefully that change won’t be too intrusive.

[lozcalver]

I’ve updated my draft PR to write the ownership when the form is submitted