On the shopping site, which step does the customer change the total number of products? How can this problem be solved?

On the shopping site, which step does the customer change the total number of products? I made a shopping site for the first time. A logical problem occurs. Ask experts to help analyze how to solve the problem. Shopping site. If only one product is left. After a user adds a shopping cart, the product is deemed to have been sold out? After the order is generated, it is regarded as sold out, or after the payment transaction is successful. If it is added to the shopping cart, it is considered as sold out. If this user is about the shopping site, which step does the customer change the total number of products at which point?
I made a shopping site for the first time. A logical problem occurs. Ask experts to help analyze how to solve the problem.

Shopping site. If only one product is left. After a user adds a shopping cart, the product is deemed to have been sold out? After the order is generated, it is regarded as sold out, or after the payment transaction is successful.

If it is added to the shopping cart, it is considered as sold out. Then, if the user is playing. Do not pay after placing it in the shopping cart. Isn't it affecting other users' shopping.

If the order is paid, it is deemed as sold out. If there is only one product left. If user A has not paid the order yet. User B ordered again. Isn't that enough?

How can we solve this problem?

------ Solution --------------------
The inventory quantity should be reduced by one when the order is generated (if it is already 0, the order cannot be generated ). If it is too early (when the shopping cart is placed), the seller suffers losses. if it is too late (when the payment is made), the seller is passive.

At the same time, we should consider adding a reminder function. when the quantity in the shopping cart exceeds the inventory quantity, we should remind the seller to pay attention, replenish the goods in time or contact the buyer.


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