Fix sort order values for existing set of models

The Sortable trait as well as the ReorderController behaviour require all models to have a consistent sort_order value.

If you are adding the Sortable trait for an existing set of models, you might get the following error message when trying to sort the models via the backend:

Illuminate\Database\QueryException: SQLSTATE[22007]: Invalid datetime format: 1366 Incorrect integer value: '' for column `db`.`acme_plugin_table`.`sort_order` at row 1

This is because all of your models currently have a sort_order value of NULL or 0.

To fix this issue, simply run the following statement in a php artisan tinker session. It will set initial sort_order values for each model.

You can set the inital order by editing the orderBy statement according to your data.

Vendor\YourPlugin\Models\YourModel
    ::orderBy('title') // Change this to modify the inital order
    ->get()
    ->map(function($model, $index) {
        $model->sort_order = $index + 1;
        $model->save();
    });

Console friendly version for pasting after your model query:

->get()->map(function($model, $index) {$model->sort_order = $index + 1;$model->save();});