Filament V3 how to save different M:M relationships using Custom Page single edit/view form?

Unimportant background:

I was able to do it with default Filament Resource before, however in my case I don't need a /table view (multiple entries with delete functionality), so I have to come up with a way to do it using a Custom page. Been stuck for a while at this now.

Did 2 simple blogs in Laravel. My second Filament project, first V3 project (trying to learn it in my free time). I ask very stupid questions from time to time, bear with me 🙇‍♂️

I want:

To save a bunch of IDs for cities and prefectures as M:M relationship (company_prefectures and company_cities) using Filament Custom Page (by Custom Page I mean single page edit/view, no table view like this one)

Solution 1?

I can save it as 2 separate multiselect JSONs with tenant ID attached in a migration as below:

Schema::create('company_regions', function (Blueprint $table) {
            $table->id();
            $table->foreignIdFor(Company::class, 'company_id')->cascadeOnDelete();
            $table->json('prefectures');
            $table->json('cities');
            $table->timestamps();
        });

But I hear JSONs are extremely heavy, especially if you need to be able to quickly search through these IDs.

Solution 2?

Save it as M:M, but I've no idea how to do it using a single custom page (Making 2 separate pages for 2-4 multiselect inputs seems like an overkill to me and is not a good UX). If it's possible, I understand I'll need 2 separate M:M tables (company_prefecture and company_city?) But if I try to pull something like that off, ->relationship returns null in my case.

Filament Relationship Documentation

I have:

My custom page (saving IDs as JSONs)

class CompanyRegions extends Page implements HasForms
{
    public function mount(): void {
        $tenant = Filament::getTenant();
        $companyID = $tenant->id;
        $companyRegions = auth()->user()->companies->find($companyID)->regions;
        
        if($companyRegions === null) {
            $this->form->fill();
        } else {
            $this->form->fill(auth()->user()->companies->find($companyID)->regions->attributesToArray());
        }
    }

    public function form(Form $form): Form
    {
        return $form
            ->schema([
                Select::make('prefectures')
                    ->placeholder('Select prefectures you work in')
                    ->label('Prefectures')
                    ->options(Prefecture::all()->pluck('prefecture_ja', 'id'))
                    ->multiple()
                    ->searchable()
                    ->required(),
                Select::make('cities')
                    ->placeholder('Select cities you work in')
                    ->label('Cities')
                    ->options(City::all()->pluck('city_ja', 'id'))
                    ->multiple()
                    ->searchable()
                    ->required(),
            ])
            ->statePath('data');
    }
  protected function getFormActions(): array {
        return [
            Action::make('save')
                ->label(__('filament-panels::resources/pages/edit-record.form.actions.save.label'))
                ->submit('Save'),
        ];
    }

    public function save(): void {
        $tenant = Filament::getTenant();
        $data = $this->form->getState();
        $data['company_id'] = $tenant->id;
        $companyID = $tenant->id;

        $company = auth()->user()->companies->find($companyID);   
        $Entry = $company->regions();

        if ($company->regions === null) {
            $Entry = new ModelsCompanyRegions;
            $Entry->fill($data);
            $Entry->save($data);
            
            Notification::make()
                ->success()
                ->title('Entry Created')
                ->send();
            } else {
                $Entry->update($data);
                Notification::make()
                ->success()
                ->title('Entry Updated)
                ->send();
           }
        }
}

Models/City.php

    public function prefecture(): BelongsTo
    {
        return $this->belongsTo(Prefecture::class);
    }

Models/CompanyRegions.php

    public function regions(): BelongsToMany
    {
        return $this->belongsToMany(Company::class);
    }
    public function cities(): BelongsToMany
    {
        return $this->belongsToMany(City::class);
    }
    public function prefectures(): BelongsToMany
    {
        return $this->belongsToMany(Prefecture::class);
    }

Models/Prefecture.php

    public function cities(): HasMany
    {
        return $this->hasMany(City::class);
    }

migrations/create_company_regions_table.php

    public function up(): void
    {
        Schema::create('company_regions', function (Blueprint $table) {
            $table->id();
            $table->foreignIdFor(Company::class, 'company_id')->cascadeOnDelete();
            // $table->foreignIdFor(City::class, 'city_id')->nullable();
            // $table->foreignIdFor(Prefecture::class, 'prefecture_id')->nullable();
            $table->json('prefectures');
            $table->json('cities');
            $table->timestamps();
        });
        // Schema::create('company_cities', function (Blueprint $table) {
        //     $table->id();
        //     $table->foreignIdFor(Company::class, 'company_id');
        //     $table->foreignIdFor(City::class, 'city_ids');
        //     $table->timestamps();
        // });
        // Schema::create('company_prefectures', function (Blueprint $table) {
        //     $table->id();
        //     $table->foreignIdFor(Company::class, 'company_id');
        //     $table->foreignIdFor(Prefecture::class, 'prefecture_ids');
        //     $table->timestamps();
        // });
    }

migrations/create_cities_table.php

        Schema::create('cities', function (Blueprint $table) {
            $table->id();
            $table->foreignIdFor(Prefecture::class, 'prefecture_id')->index();
            $table->string('city_en');
            $table->string('city_ja');
            $table->string('special_district_ja')->nullable();
            $table->timestamps();
        });

migrations/create_prefectures_table.php

        Schema::create('prefectures', function (Blueprint $table) {
            $table->id();
            $table->string('prefecture_en')->unique();
            $table->string('prefecture_ja')->unique();
            $table->timestamps();
        });

Any advice would be much appreciated