Eager Loading: Use `with` on pivot with eloquent relationship

Question

There are 4 tables:

• bundles: id, name
• products: id, name
• prices: id, name
• bundle_product: id, bundle_id, product_id, price_id

There are 3 models:

• Bundle
• Product
• Price

A Product has a Price when in a Bundle. I want to have all bundles with their associated products and associated prices. I can get all bundles with their product and the price id:

// I created a Bundle Model with a products method
class Bundle extends Model
{
    public function products()
    {
        return $this->belongsToMany(Product::class)->withPivot('price_id');
    }
}

// Then I call this in a controller
$all_bundles = Bundle::with('products')->get();

// Then I can get the price Id of the first product of the first bundle
$price_id = Bundle::with('products')->first()
    ->products()->first()
    ->pivot->price_id;

But I dont want the price id, I want the price Model. Is there any way to preload the price from the pivot (with Eager Loading)?

Answer 1

The current accepted answer deviates from the original data structure. I created a package which can help you achieve what you want and also it maintains the original data structure. Please read my medium story here: https://medium.com/@ajcastro29/laravel-eloquent-eager-load-pivot-relations-dba579f3fd3a

First, create your custom pivot model and define relations on pivot model, in your case:

use Illuminate\Database\Eloquent\Relations\Pivot;

class BundleProduct extends Pivot
{
    public function price()
    {
        return $this->belongsTo(Price::class);
    }
}

Then use the pivot model in the relation:

class Bundle extends Model
{
    public function products()
    {
        return $this->belongsToMany(Product::class)
        ->withPivot('price_id') // this is needed to query the relation `price`
        ->using(BundleProduct::class);
    }
}

Make sure you use the trait AjCastro\EagerLoadPivotRelations\EagerLoadPivotTrait in the Product model because it is the related model in belongsToMany relation. This let us enable eager loading the pivot relations.

use AjCastro\EagerLoadPivotRelations\EagerLoadPivotTrait;

class Product extends Model 
{
  use EagerLoadPivotTrait;
}

Then eager load it like this:

$bundle = Bundle::with('products.pivot.price')->first();
$price = $bundle->products->first()->pivot->price;