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カード削除

To delete cards, we need to create a new API in PHP that

  • Receives the user id
  • Receives a list of card ids to remove (including duplicates)
  • Runs an SQL query that reduces the count by 1 for each card that matches the request
  • If the count reaches zero, remove the record from the database

Removing cards using SQL

First, let's see how decreasing the count in SQL would look like. Let's say we want to decrease user_id = 1, card_id = 1 by two cards. Since this user has 2 cards of card_id = 1, this would remove all cards. We can decrease the count by telling MySQL to subtract 2 from the field "count" like so:

UPDATE user_cards SET count = count - 2 WHERE user_id = 1 and card_id = 1;

This is telling MySQL to take the column "count" and subtract it by 2, but only for user_id = 1and card_id = 1. After running it we get:

image.png

We can check that the count went to zero. All we have to do next is remove all records where count is 0. We can easily do that with DELETE.

DELETE FROM user_cards WHERE count = 0;

We can use these two instructions in PHP to remove cards from players. Let's design our API

PHP スクリプト

Before we get started, let's restore our database. Run the following SQL command in phpMyAdmin:

REPLACE INTO `user_cards` (`id`, `user_id`, `card_id`, `count`) VALUES
(1, 1, 1, 2), (2, 1, 2, 1), (3, 1, 5, 1),(4, 1, 8, 2),
(5, 1, 6, 1), (6, 2, 3, 5), (7, 2, 6, 3),(8, 2, 12, 1);

Now, let's design our script. Create a new file called delete_player_cards.php.  In our API, we are going to request the client to send us the user id and how many cards to delete for each card id. Since the amount of cards to be deleted is variable, we are going to request the client to send the cards to be deleted as a JSON object that looks like this:

 

 

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