Consider link between submission and custom data model entries

[dave-mills]

A submission() relationship on a data model might be hard to do, as it would ideally require the opposite relationship on the submission (only possible if the dev created a custom Submission model in the application).

...is that correct? The Spatie Tags package puts a morphToMany relationship on their HasTags trait, (here), and does not have a corresponding relationship on the Tag model itself (because they do not know what models will be used). So maybe we do something like that?