Support relations with the Repeater field

[Flynsarmy]

Relation formwidget currently only supports JSON fields. I'd like it to also support model relations.

I made an example RelatedRepeater formwidget by extending Repeater to demonstrate how this might work. Code available here:
https://github.com/Flynsarmy/wn-relatedrepeater-plugin

The code is ugly as sin but it appears to work perfectly for hasMany relations and could be merged back into Repeater when done. I haven't tested other relation types.

Would love some testing for any edge cases, other relation types etc. I'm happy to keep working on this.

[bennothommo]

@Flynsarmy great work on this. My only notes would be:

• This explicitly would require the related model to support sorting, so a check would need to be done to ensure that the related model is using the Sortable trait.
• I imagine that this could only work for hasMany relations, as the morph relations would possibly require an extra step in selecting the target morph model. hasOne and belongsTo can already be handled by other fields, and hasManyThrough might not be easily established since there's an intermediate model.
• How would repeater limits be handled with a relation? (Or more to the point, what would occur if a limit is established on a repeater but that limit is breached by the number of related records? Would the other records be dropped?)
• Following on from the above, would removing the item from the repeater delete the relation?

[Flynsarmy]

Thanks Ben this was exactly what I needed!

a check would need to be done to ensure that the related model is using the Sortable trait.

Added. When using a RelationRepeater, the formwidget will be sortable when the relation class uses the Sortable trait, and isn't sortable when the relation doesn't include the trait.

I imagine that this could only work for hasMany relations

I've locked the widget to only work as a RelationRepeater when the relation is a hasMany. I'll still explore the other relation types but for the time being we can just start with this.

what would occur if a limit is established on a repeater but that limit is breached by the number of related records

This is already covered by existing checks. A popup appears stating option_values only allows up to 2 items, 3 were provided. The admin will need to remove the excess records before continuing.

would removing the item from the repeater delete the relation

It currently orphans the record in the database. I think it would be more appropriate to delete the record though.

My repo has been updated with the latest version of the formwidget.

[Flynsarmy]

Currently waiting on #506 before this can continue

[bennothommo]

Merged it @Flynsarmy

[Flynsarmy]

My repo has been updated to use the new sorting functionality. If I've addressed all your concerns above, I'll start a WIP PR so we can clean up the code. Otherwise let me know if there's anything you'd like changed.

[bennothommo]

@Flynsarmy happy for you to proceed with the PR.