首先，创建一个Product模型：

use Jenssegers\Mongodb\Eloquent\Model;

class Product extends Model
{
    protected $collection = 'products_1';
}

然后尝试在whereRaw函数中使用$unionWith聚合：

$products = Product::whereRaw(function($collection) {
    return $collection->aggregate([
        [
            '$unionWith' => [
                'coll' => 'products_2',
            ]
        ],
        [
            '$unionWith' => [
                'coll' => 'products_3',
            ]
        ],
        [
            '$unionWith' => [
                'coll' => 'products_4',
            ]
        ],
    ]);
})->paginate(5);

参考：

• https://www.mongodb.com/docs/manual/reference/operator/aggregation/unionWith/
• https://github.com/jenssegers/laravel-mongodb/issues/2235

如果不起作用，请尝试raw与toQuery：

$products = Product::raw(function($collection) {
    return $collection->aggregate([
        [
            '$unionWith' => [
                'coll' => 'products_2',
            ]
        ],
        [
            '$unionWith' => [
                'coll' => 'products_3',
            ]
        ],
        [
            '$unionWith' => [
                'coll' => 'products_4',
            ]
        ],
    ]);
})->toQuery()->paginate(5);

参考：https://github.com/jenssegers/laravel-mongodb/issues/1574

我觉得最好的方法是定义集合的模型，因为关系数据库使用表，而像mongo这样的非关系数据库使用集合，我建议您在模型类中定义mongo集合。
就像普通模型一样，MongoDB模型类会根据模型名称知道使用哪个集合，对于Products，将使用集合Products。

use Jenssegers\Mongodb\Eloquent\Model;

class Book extends Model
{
    protected $collection = 'products';
}