Combine 2 eloquent result and update them - php

Question

I have two tables that have relation each other :
1st table products migration :
Schema::create('products', function (Blueprint $table) {
$table->id();
$table->string('name');
$table->timestamps();
});
2nd table discount migration :
Schema::create('discounts', function (Blueprint $table) {
$table->id();
$table->foreignId('product_id');
$table->double('rate', 8, 2); // rates between 0.05 ~ 0.2
$table->foreignId('period_id');
$table->timestamps();
});
Product model :
/**
* Get the product associated with discount.
*/
public function discounts()
{
return $this->hasMany(Discount::class);
}
Discount model :
/**
* Get the discount associated with product.
*/
public function product()
{
return $this->belongsTo(Product::class);
}
What i've tried so far is a bit silly :
$productWithoutDiscount = Product::doesntHave('discounts')
->where([
['section', Session::get('section-budget')],
['status', 'PREPARED']
])->get();
$productWithDiscount = Product::with('discount')->whereHas('discounts', function ($query) {
$query->where('rate' ,'>', 0.05);
})->get();
$productAll = $productWithoutDiscount->merge($productWithDiscount);
Above code works, however, i also need to update them, that wont happened as the merged eloqunet instance will be converted to collection (which doesn't have access to update() method)
How can i get both the product which don't have discount AND product which have discount with above 0.05 rate and update them ?
Update 1
So i follow #Salvon's advice to use union, so these my following code atm :
$productAll = Product::with('discount')->whereHas('discounts', function ($query) {
$query->where('rate' ,'>', 0.05);
})->union(Product::doesntHave('discounts')
->where([
['section', Session::get('section-budget')],
['status', 'PREPARED']
]));
Then another problem came out, because when i execute the update method like so :
try {
$productAll->update([
'period_id' => Session::get('period');
]);
return response()->json([
'message' => 'Data successfully updated.'
], 201);
} catch (\Throwable $th) {
return response()->json([
'message' => $th->getMessage()
], 500);
}
nothing was updated and not even any error come out,
Already check the protected $fillable on my model and the 'period_id' is there.
how can I solved this ?
Update 2
Weird after i cahge the order of query like so :
$productAll = Product::doesntHave('discounts')->where([
['section', Session::get('section-budget')],
['status', 'PREPARED']
])->union(Product::with('discount')->whereHas('discounts', function ($query) {
$query->where('rate' ,'>', 0.05);
}));
The update() method works. What is the cause ?