Backpack 4.1 HasMany relation

App\Http\Controllers\PostCrudController

  <?php

namespace App\Http\Controllers;

use Backpack\CRUD\app\Http\Controllers\CrudController;
use Backpack\CRUD\app\Library\CrudPanel\CrudPanelFacade as CRUD;

class PostCrudController extends CrudController
{
    use \Backpack\CRUD\app\Http\Controllers\Operations\CreateOperation { store as traitStore; } //IMPORTANT HERE
    use \Backpack\CRUD\app\Http\Controllers\Operations\UpdateOperation { update as traitUpdate; } //IMPORTANT HERE
    
    public function setup()
    {
        CRUD::setModel(\App\Models\Post::class);
        CRUD::setRoute(config('backpack.base.route_prefix') . '/post');
        CRUD::setEntityNameStrings('post', 'posts');
    }

    protected function setupCreateOperation()
    {
        CRUD::field('post_title');
        CRUD::field('post_body');

        CRUD::field('comments_list')
            ->type('repeatable')
            ->label('Comments')
            ->fields([
                [
                    'name'    => 'id',
                    'type'    => 'hidden',
                ],
                [
                    'name'    => 'comment_text',
                    'type'    => 'text',
                ],
            ]);
    }

    protected function setupUpdateOperation()
    {
        $this->setupCreateOperation();
    }

    public function store()
    {
        $items = collect(json_decode(request('comments_list'), true));

        // create the main item as usual
        $response = $this->traitStore();

        // instead of returning, take a little time to create the post comments too
        $post_id = $this->crud->entry->id;
        
        
        // add the post_id to the items collection
        $items->each(function($item, $key) use ($post_id) {
            $item['post_id'] = $post_id;     
            \App\Models\Comment::create($item);
        });

        return $response;
    };

    public function update()
    {
        $items = collect(json_decode(request('comments_list'), true));

        $response = $this->traitUpdate();

        // instead of returning, take a little time to update the post comments too
        $post_id = $this->crud->entry->id;
        $created_ids = [];

        $items->each(function($item, $key) use ($post_id, &$created_ids) {
            $item['post_id'] = $post_id;

            if ($item['id']) {
                $comment = \App\Models\Comment::find($item['id']);
                $comment->update($item);
            } else {
                
               $created_ids[] = \App\Models\Comment::create($item)->id;
                
            }

        });
        
        // delete removed Comments
        $related_items_in_request = collect(array_merge($items->where('id', '!=', '')->pluck('id')->toArray(), $created_ids));
        $related_items_in_db = $this->crud->entry->comments;
        
        $related_items_in_db->each(function($item, $key) use ($related_items_in_request) {
            if (!$related_items_in_request->contains($item['id'])) {
                $item->delete();
            }
        });

        return $response;
    }

App\Models\Comment

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Comment extends Model
{
    use \Backpack\CRUD\app\Models\Traits\CrudTrait;
    
    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $fillable = [
        'post_id',
        'comment_text',
    ];

    /**
     * The attributes that should be cast to native types.
     *
     * @var array
     */
    protected $casts = [
        'id' => 'integer',
        'post_id' => 'integer',
    ];


    public function post()
    {
        return $this->belongsTo(\App\Models\Post::class);
    }
}

App\Models\Post

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    use \Backpack\CRUD\app\Models\Traits\CrudTrait;

    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $fillable = [
        'post_title',
        'post_body',
    ];

    /**
     * The attributes that should be cast to native types.
     *
     * @var array
     */
    protected $casts = [
        'id' => 'integer',
    ];

    public function comments()
    {
        return $this->hasMany(\App\Models\Comment::class);
    }
    
    //acessor to get the comments populated in the repeatable field again
    public function getCommentsListAttribute() {
        return json_encode($this->comments);
    }
}

for everyone in the same situation I found a solution, force the language at the beginning of the setupCreateOperation() function:

app()->setlocale(request('locale')?:'en');