Detailed explanation of transaction processing mechanism in PHP database connection

The transaction processing mechanism in PHP is designed to ensure the integrity of database operations. It allows a set of operations to be executed in full or in none. This is accomplished by starting a transaction, performing operations, and committing or rolling back the transaction as appropriate. By using transactions, you can ensure that the database remains consistent during updates.

Detailed explanation of transaction processing mechanism in PHP database connection

Transaction processing

Transaction processing is a series of operations that maintain the integrity of the database and ensure the consistency of the database. In PHP, you can use transactions to ensure that either all or none of a set of operations are performed.

Transaction Functions

To start a transaction, you can use the following functions:

mysqli_begin_transaction($mysqli);

Once the transaction has started, you can perform operations. After all operations have been performed, the transaction can be committed or rolled back:

mysqli_commit($mysqli); //提交事务
mysqli_rollback($mysqli); //回滚事务

Practical Case

Suppose we have an e-commerce website through which users can purchase goods. When a user places an order, the following three tables need to be updated:

• users table - user information
• orders table - order information
• order_items Table - Items included in the order

In order to ensure the integrity of these three tables, we can use transaction processing during the order process:

<?php
$mysqli = new mysqli("localhost", "root", "password", "ecomm");

// 开启事务
$mysqli->begin_transaction();

try {
    // 更新 users 表
    $sql = "UPDATE users SET balance = balance - ? WHERE id = ?";
    $stmt = $mysqli->prepare($sql);
    $stmt->bind_param("di", $_POST['balance'], $_POST['user_id']);
    $stmt->execute();

    // 更新 orders 表
    $sql = "INSERT INTO orders (user_id, total_amount) VALUES (?, ?)";
    $stmt = $mysqli->prepare($sql);
    $stmt->bind_param("di", $_POST['user_id'], $_POST['total_amount']);
    $stmt->execute();

    // 更新 order_items 表
    foreach ($_POST['items'] as $item) {
        $sql = "INSERT INTO order_items (order_id, product_id, quantity, unit_price) VALUES (?, ?, ?, ?)";
        $stmt = $mysqli->prepare($sql);
        $stmt->bind_param("iiii", $last_inserted_order_id, $item['product_id'], $item['quantity'], $item['unit_price']);
        $stmt->execute();
    }

    // 提交事务
    $mysqli->commit();
    echo "Order placed successfully!";
} catch (Exception $e) {
    // 如果出现异常，回滚事务
    $mysqli->rollback();
    echo "An error occurred while placing the order.";
}
?>

In the above code, we first start a transaction, and then try to perform three operations to update the table. If all operations succeed, the transaction is committed. If one of the operations fails, the transaction is rolled back and an error message is displayed to the user.

Notes

When using transaction processing, you need to pay attention to the following points:

• All operations in the transaction must be in the same database Executed during connection.
• All operations in a transaction must be atomic, meaning that they are either all executed or none of them are executed.
• Transactions may cause deadlocks, so care needs to be taken when designing transaction processing code.

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