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## User Model
Add the `CanPay` trait and `Customer` interface to your User model.
> The trait `CanPay` already inherits `HasWallet`, reuse will cause an error.
```php
use Bavix\Wallet\Traits\CanPay;
use Bavix\Wallet\Interfaces\Customer;
class User extends Model implements Customer
{
use CanPay;
}
```
## Item Model
Add the `HasWallet` trait and interface to `Item` model.
Starting from version 9.x there are two product interfaces:
- For an unlimited number of products (`ProductInterface`);
- For a limited number of products (`ProductLimitedInterface`);
An example with an unlimited number of products:
```php
use Bavix\Wallet\Traits\HasWallet;
use Bavix\Wallet\Interfaces\Customer;
use Bavix\Wallet\Interfaces\ProductInterface;
class Item extends Model implements ProductInterface
{
use HasWallet;
public function getAmountProduct(Customer $customer): int|string
{
return 100;
}
public function getMetaProduct(): ?array
{
return [
'title' => $this->title,
'description' => 'Purchase of Product #' . $this->id,
];
}
}
```
Example with a limited number of products:
```php
use Bavix\Wallet\Traits\HasWallet;
use Bavix\Wallet\Interfaces\Customer;
use Bavix\Wallet\Interfaces\ProductLimitedInterface;
class Item extends Model implements ProductLimitedInterface
{
use HasWallet;
public function canBuy(Customer $customer, int $quantity = 1, bool $force = false): bool
{
/**
* This is where you implement the constraint logic.
*
* If the service can be purchased once, then
* return !$customer->paid($this);
*/
return true;
}
public function getAmountProduct(Customer $customer): int|string
{
return 100;
}
public function getMetaProduct(): ?array
{
return [
'title' => $this->title,
'description' => 'Purchase of Product #' . $this->id,
];
}
}
```
I do not recommend using the limited interface when working with a shopping cart.
If you are working with a shopping cart, then you should override the `PurchaseServiceInterface` interface.
With it, you can check the availability of all products with one request, there will be no N-queries in the database.
## Proceed to purchase
Find the user and check the balance.
```php
$user = User::first();
$user->balance; // 100
```
Find the goods and check the cost.
```php
$item = Item::first();
$item->getAmountProduct($user); // 100
```
The user can buy a product, buy...
```php
$user->pay($item);
$user->balance; // 0
```
What happens if the user does not have the funds?
The same as with the [withdrawal](withdraw#failed).
```php
$user->balance; // 0
$user->pay($item);
// throw an exception
```
The question arises, how do you know that the product is purchased?
```php
(bool)$user->paid($item); // bool(true)
```
## Safe Pay
To not write `try` and `catch` use `safePay` method.
```php
if ($user->safePay($item)) {
// try to buy again )
}
```
It worked!