Eager load polymorphic relationships with constrain()

[kiritokatklian]

I’ve searched Nova docs, Laracasts, and this repo for a way to eager load polymorphic relationships using constrain(), but I couldn’t find any support.

Currently, you can only eager load using the static $with property, but expressions aren’t allowed. I’d like a static method of $with that allows eager loading with expressions, like this:

public static function with()
{
    return [
        'model' => function ($morphTo) {
            $morphTo->constrain([
                \App\Models\Foo::class => function ($query) {
                    $query->with(['relation']);
                },
                \App\Models\Bar::class => function ($query) {
                    $query->with(['different_relation']);
                },
                \App\Models\Baz::class => function ($query) {
                    // No eager loading necessary
                }
            ]);
        }
    ];
}

I noticed that Resource inherits a similar method from \Illuminate\Database\Eloquent\Model which I can override, but it has no effect as it’s not(?) used by Nova. Usually this method is something the user calls, so it makes sense

public static function with($relations)
{
    return static::query()->with(
        is_string($relations) ? func_get_args() : $relations
    );
}

I needed this because I have models where I want to eager load a translations relationship that other models don’t have. This results in an error because the relationship can’t be found in the models that lack it.

Perhaps I'm looking in the wrong places. If you know of another solution, I’m open to suggestions.

[kiritokatklian]

I can't believe I completely forgot the existence of the indexQuery() method.
I used the following for eager loading:

public static function indexQuery(NovaRequest $request, $query): Builder
{
    return parent::indexQuery($request, $query)
        ->with([
            'model' => function ($morphTo) {
	            $morphTo->constrain([
	                \App\Models\Foo::class => function ($query) {
	                    $query->with(['relation']);
	                },
	                \App\Models\Bar::class => function ($query) {
	                    $query->with(['different_relation']);
	                },
	                \App\Models\Baz::class => function ($query) {
	                    // No eager loading necessary
	                }
	            ]);
        	}
		]);
}