MorphToMany Accessing Blank Models?

[jjjrmy]

• Laravel Version: 8
• Nova Version: 3.31
• PHP Version: 8
• Database Driver & Version: MySQL

Description:

If you add a Ray debug to the relationship method, the API request is returning blank models as shown below when accessing a Post resource.

class Post extends Model {
  public function tags() {
     ray(request()->url(), $this)->label(__FUNCTION__);
     return $this->morphToMany(Tag::class, 'taggable');
  }
}

In my example this Post has 3 Tags, and it seem to be outputting 3 blank Post models in the debug output.
This is causing me problems and doesn't seem right.

Why is this happening and is there a way to prevent it?

Detailed steps to reproduce the issue on a fresh Nova installation:

1.) Follow this structure for creating Laravel & Nova Models:
https://laravel.com/docs/8.x/eloquent-relationships#many-to-many-polymorphic-relations
2.) Create / Seed the Tags and Posts + Videos
3.) Navigate to a Post

[jjjrmy]

@crynobone can you please tell me what info is needed?

[crynobone]

All bug report should come with full reproducing code, not just code snippets.

[jjjrmy]

You can just copy the code from the Laravel documentation, but here it is...
Migration

class CreateMorphsTable extends Migration
{
    public function up()
    {
        Schema::create('posts', function (Blueprint $table) {
            $table->id();
            $table->text('name');
            $table->timestamps();
        });
        Schema::create('videos', function (Blueprint $table) {
            $table->id();
            $table->text('name');
            $table->timestamps();
        });
        Schema::create('tags', function (Blueprint $table) {
            $table->id();
            $table->text('name');
            $table->timestamps();
        });
        Schema::create('taggables', function (Blueprint $table) {
            $table->id();
            $table->foreignId('tag_id');
            $table->morphs('taggable');
            $table->timestamps();
        });
    }
}

Models

class Video extends Model
{
    public function tags()
    {
        return $this->morphToMany(Tag::class, 'taggable');
    }
}

class Post extends Model
{
    public function tags()
    {
        ray(request()->url(), $this)->label(__FUNCTION__);
        return $this->morphToMany(Tag::class, 'taggable');
    }
}

class Tag extends Model
{
    public function posts()
    {
        return $this->morphedByMany(Post::class, 'taggable');
    }

    public function videos()
    {
        return $this->morphedByMany(Video::class, 'taggable');
    }
}

Nova Models

class Video extends Resource
{
    public function fields(Request $request)
    {
        return [
            ID::make(__('ID'), 'id')->sortable(),
            Text::make('Name'),
            MorphToMany::make('Tags'),
        ];
    }
}

class Post extends Resource
{
    public function fields(Request $request)
    {
        return [
            ID::make(__('ID'), 'id')->sortable(),
            Text::make('Name'),
            MorphToMany::make('Tags'),
        ];
    }
}

class Tag extends Resource
{
    public function fields(Request $request)
    {
        return [
            ID::make(__('ID'), 'id')->sortable(),
            Text::make('Name'),
        ];
    }
}

[jjjrmy]

I know it's doing something it shouldn't because if you access Post::first()->tags it will Ray dump just 1 instance of the Post model and no other blank models, but what ever is happening in the API Resource is calling those extra blank models.

[crynobone]

Calling blank model occurred in some API request and that is to be expected depending on what information needed for that particular API request.

I don't think there any bug here, as that is expected behaviour.

[jjjrmy]

@crynobone
Can you please explain more because this doesn't seem to be expected behavior...

If you do Post::find(1)->tags in Tinkerwell, Ray will only dump one output of the Post model.
If you access /nova/resources/posts/1 it calls the API /nova-api/tags?...&viaResource=posts&viaResourceId=1&viaRelationship=tags&relationshipType=morphToMany, Ray will dump as shown in the image above.
(In both cases 3 tags are attached to the Post.)

They are both accessing the same data, what ever is happening in that API endpoint I wouldn't call "to be expected" as that doesn't occur when doing it outside of Nova.

What is happening in the endpoint that is causing this?

[crynobone]

above are only your expectations, what we do is only Tag::query(), new Tag() or Tag::find()

[jjjrmy]

That makes sense but why would any of those return blank models of the Post?

[davidhemphill]

Depending on the setup, Nova sometimes spins up a resource that doesn't have a Model instance hydrated. For example, if the field is set up to not defer the query (e.g a Select field with its options directly querying the database like Select::make('Type')->options(Type::all()) and not returned from a Closure), then Nova can sometimes access those relationships and they'll be empty. That's just one example. Nova does A LOT of this kind of thing.

What we need you to provide is the full reproducing code, along with descriptions of the problems you're facing. "This is causing me problems and doesn't seem right." is a little vague. Will be glad to turn this back into an issue once we get that. Thanks!

[jjjrmy]

The code I posted reproduces the issue I'm seeing..

In my attribute/relationship it calls relationships to other models which don't exist because the model is empty.
So is the solution to make a check if the model is empty before returning anything?

If you look at my example code, it's not using a Select field.
To me this seems like a Nova only issue/workaround?

[davidhemphill]

I'm just curious, wouldn't the field need to be a MorphMany, and not a MorphToMany?

[jjjrmy]

I can try that but I'm just copying the relationship setup as mentioned here: https://laravel.com/docs/8.x/eloquent-relationships#many-to-many-polymorphic-relations

Post -> morphToMany -> Tags
Video -> morphToMany -> Tags

Tag -> morphedByMany -> Posts/Videos

[jjjrmy]

Okay so I switched the relationship on Nova to MorphMany and kept the actual Model Relationship is still MorphToMany, and it seems to be working now with no issues of running additional blank models.

But I'm still curious as to why this is happening, to me it still seems like a bug.

[crynobone]

MorphToMany is correct usage since you have a pivot table taggable. You are not seeing empty model access there since it doesn't need to check for pivot as MorphMany doesn't have it.

[crynobone]

Calling blank model occurred in some API request and that is to be expected depending on what information needed for that particular API request.

    /**
     * Get all of the tags for the post.
     *
     * @return \Illuminate\Database\Eloquent\Relations\MorphToMany
     */
    public function tags()
    {
        ray(request()->fullUrl(), $this, collect(debug_backtrace())->transform(function ($stack) {
            if (!isset($stack['file']) || !isset($stack['line'])) {
                return null;
            }

            return $stack['file'].':'.$stack['line'];
        })->all())->label(__FUNCTION__);
        
        return $this->morphToMany(Tag::class, 'taggable')->withPivot('notes');
    }

Code above added to Post model on nova-dusk-suite which has a similar setup to the posted code.

Line 707 on ResolvesFields.php class is where we call Post::tags() to get an instance of Illuminate\Database\Eloquent\Relations\MorphToMany (and not Post model) which allows us to retrieve the pivot accessor, we're not pulling any data for that purpose and that's the intended behavior