Laravel - how to eager load relation of custom intermediate table - php

Question

I have three models, SalesReturn, Product and ProductSalesReturn, and their relations are following:
class SalesReturn extends Model
{
public function products()
{
return $this->belongsToMany(Product::class)
->withTimestamps()
->using(ProductSalesReturn::class);
}
}
I use the ProductSalesReturn to represent the intermediate table ( https://laravel.com/docs/6.x/eloquent-relationships#defining-custom-intermediate-table-models ), and ProductSalesReturn has a relation to Unit:
class ProductSalesReturn extends Pivot
{
public function unit()
{
return $this->belongsTo(Unit::class);
}
}
When I eager loading the unit relation like following code:
SalesReturn::with(['products', 'products.unit'])->find($id);
I will get the following error:
SQLSTATE[42S22]: Column not found: 1054 Unknown column 'units.product_id' in 'where clause' (SQL: select * from `units` where `units`.`product_id` in (1031, 1631, 13391, 14361, 16981, 17441, 41982, 45982, 55741) and `units`.`deleted_at` is null)
The table schemas are following:
CREATE TABLE `sales_returns` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`number` varchar(20) COLLATE utf8mb4_unicode_ci NOT NULL,
`user_id` bigint(20) NOT NULL,
`order_id` bigint(20) NOT NULL,
`note` text COLLATE utf8mb4_unicode_ci NOT NULL,
`created_at` timestamp NULL DEFAULT NULL,
`updated_at` timestamp NULL DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
CREATE TABLE `product_sales_return` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`sales_return_id` bigint(20) NOT NULL,
`product_id` bigint(20) NOT NULL,
`unit_id` bigint(20) NOT NULL,
`price` double NOT NULL,
`amount` int(11) NOT NULL,
`gross_profit` double NOT NULL DEFAULT '0',
`created_at` timestamp NULL DEFAULT NULL,
`updated_at` timestamp NULL DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
How can I eager loading the relation of custom intermediate table in Laravel ?
Thank you.

Answer 1

You could use Laravel Eloquent: Eager Load Pivot Relations
Installation
composer require ajcastro/eager-load-pivot-relations
Configuration
use AjCastro\EagerLoadPivotRelations\EagerLoadPivotTrait;
class Product extends Model
{
// Use the trait here to override eloquent builder.
// It is used in this model because it is the relation model defined in
// SalesReturn::products() relation.
use EagerLoadPivotTrait;
}
Usage
return SalesReturn::with('products.pivot.unit')->get();
Define the table, foreignPivotKey and relatedPivotKey paramethers in your produtcts belongsToMany relationship