How can I dynamically decide which relationships to eager load based on usage

Use a custom scope

You can define a custom scope on your model that eager loads relationships based on certain conditions:

php
// Post.php
class Post extends Model
{
    public function scopeWithEagerLoadedRelations($query)
    {
        return $query->with(['comments', 'author']);
    }
}

Then in your controller:

php
// PostsController.php
public function index()
{
    $posts = Post::withEagerLoadedRelations()->get();
}

This allows you to eager load specific relationships based on the needs of the current request.

Use a custom collection class

You can create a custom collection class that eager loads relationships based on the current instance:

php
// PostCollection.php
class PostCollection extends Collection
{
    public function eagerLoadRelations()
    {
        if ($this->first()->relationLoaded('comments')) {
            $this->load('comments');
        }
        
        if ($this->first()->relationLoaded('author')) {
            $this->load('author');
        }
        
        return $this;
    }
}

Then in your model:

php
// Post.php
class Post extends Model
{
    public function newCollection(array $models = [])
    {
        return new PostCollection($models);
    }
}

And in your controller:

php
// PostsController.php
public function index()
{
    $posts = Post::all()->eagerLoadRelations();
}

This allows you to eager load relationships based on whether they are already loaded on the first model instance.

Use a custom macro

You can define a custom macro on the `Collection` class to eager load relationships based on usage:

php
// AppServiceProvider.php
public function boot()
{
    Collection::macro('eagerLoadRelations', function () {
        $relations = [];
        
        if ($this->first()->relationLoaded('comments')) {
            $relations[] = 'comments';
        }
        
        if ($this->first()->relationLoaded('author')) {
            $relations[] = 'author';
        }
        
        return $this->load($relations);
    });
}

Then in your controller:

php
// PostsController.php
public function index()
{
    $posts = Post::all()->eagerLoadRelations();
}

This allows you to eager load relationships based on whether they are already loaded on the first model instance, using a global macro.

By using these techniques, you can dynamically decide which relationships to eager load based on the current usage of the models in your application.