如何正确使用 Laravel 关系呢？

Question

I have the following table structure:

users:
    id
    name
    
products:
    id
    name    
    
orders:
    id
    user_id
    product_id
    paid (boolean)

order_items:
    order_id
    product_id
    

Using relationships, what would be the best way to get all the products that user 1 bought and paid for? Also, how can I pass a product ID, and check if user 1 has paid for this product?

Answer 1

Add user_id to order_items table, this will make things easier. Then you can add necessary relationships to your models:

User:

public function orders(): HasMany 
{
    return $this->hasMany(Order::class);
}

public function paidOrders(): HasMany 
{
    return $this->hasMany(Order::class)
        ->where('paid', true);
}

public function products(): BelongsToMany
{
    return $this->belongsToMany(
        Product::class, 
        'order_items', 
        'user_id', 
        'product_id'
    );
}

public function paidProducts(): BelongsToMany
{
    return $this->products()
        ->whereRelation('orders', 'paid', true);
}

public function hasPaidForProduct(Product|string $product): bool
{
    if($product instanceof Product) {
        $product = $product->getKey();
    }

    return $this->paidProducts()
        ->wherePivot('product_id', $product)
        ->exists();
}

Product:

public function orders(): BelongsToMany 
{
    return $this->belongsToMany(
        Order::class, 
        'order_items', 
        'product_id', 
        'order_id'
    );
}

public function users(): BelongsToMany 
{
    return $this->belongsToMany(
        User::class, 
        'order_items', 
        'product_id', 
        'user_id'
    );
}

Order:

public function products(): BelongsToMany 
{
    return $this->belongsToMany(
        Product::class, 
        'order_items', 
        'order_id', 
        'product_id'
    );
}

public function user(): BelongsTo 
{
    return $this->belongsTo(User::class);
}

Creating an order would be like this:

$user = $request->user();

$products = ... // e.g. Cart::getItems();

$orderData = [
    'paid' => false,
    ...
];

$attachData = [];

// Here, we are preparing order products and the additional data, 
// aka user_id, for order_items table. The table will be like this:
// +----------+------------+---------+
// | order_id | product_id | user_id |
// +----------+------------+---------+
// |        1 |          1 |       1 |
// |        1 |          2 |       1 |
// |        1 |          3 |       1 |
// +----------+------------+---------+
foreach($products as $product) {
    $attachData[$product->id] = [
        'user_id' => $user->id,
    ];
}

$order = DB::transaction(function() use ($user, $orderData, $attachData) {
    $order = $user->orders()
        ->create($orderData);

    $order->products()
        ->attach($attachData);

    return $order;
});

Then;

// All products that the user has ordered.
$user->products;

// All products that the user has ordered and paid for.
$user->paidProducts;

$inquiredProduct = Product::findOrFail(1);

$user->hasPaidForProduct($inquiredProduct) // true/false