To ensure that the related data is pre-selected in a Select field in Laravel Filament you need to set the value of the field to the data from the model that you’re editing.

Since you are using a hasMany relationship the issue is that Select::make is expecting a single value or an array of values but you’re working with a collection of related models.

In your case since the relationship is hasMany you can retrieve the related data from the AddOn.php model and pass it as the value to the Select field.

Look at this code

First modify the Select field to pre-select related values

// In the AddOnResource
Select::make('vehicle_type')
    ->multiple()
    ->label('Vehicle Type')
    ->options(function () {
        return \App\Models\VehicleType::pluck('name', 'id');
    })
    ->searchable()
    ->placeholder('Vehicle Type')
    ->required()
    ->default(function ($record) {
        return $record->addOnVehicleType->pluck('vehicle_type_id')->toArray();
    }),

then update the relationship method on the model like this

public function addOnVehicleType() {
    return $this->hasMany(AddOnVehicleType::class);
}

The AddOnVehicleType table must have the appropriate foreign keys to store the relation hasMany. Save the selected vehicle_type correctly when updating the AddOn.php resource 👋