John Davidson

Message:

I have a Laravel 9 project with a Nova 4 admin panel and the following set of relationships: there's the Attribute entity that defines a particular attribute (e.g. Project Type, Rating, etc.). A typical attribute is linked to several values that it can have (e.g. Project Type 1, Project Type 2, Project Type 3). These values are represented by the Option entity, thus there's a one-to-many relationship between attributes and options. Finally, there the Contractor entity, which these attributes can be attached to, so we have a many-to-many relationship between contractors and options.

Back to Nova, I wanted to be able to attach options to a contractor I select in the contractors detail page and also to attach contractors to a selected option in the options detail page. Using the BelongsToMany Nova class I connected these two entities, but the problem is that when attaching an option to a contractor, it shows only one dropdown with all options available without specifying attributes. Is there a way to have two dropdowns, one for attributes, and another one for options, which would be depending on which attribute has been selected?

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My Answer:
Yes, you can customize the attach page in Nova to enhance specificity for a particular type of relationship. One way to achieve this is by creating a custom field in Nova that dynamically populates options based on the selected attribute.

You can create a custom field by extending the BelongsToMany field class and overriding the `fillAttributeFromRequest` method to customize the behavior of the field. Within this method, you can fetch the selected attribute and dynamically populate the options dropdown based on the attribute.

Here's an example of how you can achieve this:

php
use Laravel\Nova\Fields\BelongsToMany;

class CustomBelongsToMany extends BelongsToMany
{
public function fillAttributeFromRequest(NovaRequest $request, $requestAttribute, $model, $attribute)
{
$attributeId = $request->get('attribute_id');
$options = Option::where('attribute_id', $attributeId)->get();

$this->options($options);

parent::fillAttributeFromRequest($request, $requestAttribute, $model, $attribute);
}
}


In your Nova resource file, you can use the custom field instead of the default BelongsToMany field:

php
use App\Nova\CustomBelongsToMany;

BelongsToMany::make('Options', 'options', CustomBelongsToMany::class)
->options(Option::all())
->display('name')
->searchable();


This way, when attaching options to a contractor, the options dropdown will be dynamically populated based on the selected attribute. You can further customize the behavior and appearance of the custom field to suit your specific requirements.