How to implement deletion of data function in PHP

PHP is a server-side scripting language widely used in web development, especially dynamic page generation. In web development, we often need to delete data from the database. PHP provides us with a variety of ways to delete data. This article will introduce several commonly used ways to delete data in PHP.

1. Using the DELETE statement

The DELETE statement is a common way to delete data in the database. In PHP, we can use mysqli extension or PDO extension to execute DELETE statement.

Use mysqli extension:

$mysqli = new mysqli("localhost", "username", "password", "database");

// 检查连接是否成功
if ($mysqli->connect_errno) {
  echo "连接 MySQL 失败：" . $mysqli->connect_error;
}

// 执行 DELETE 语句
$sql = "DELETE FROM users WHERE id=1";
if ($mysqli->query($sql) === TRUE) {
  echo "删除成功";
} else {
  echo "Error: " . $sql . "<br>" . $mysqli->error;
}

// 关闭连接
$mysqli->close();

Use PDO extension:

$dsn = "mysql:host=localhost;dbname=database";
$username = "username";
$password = "password";

try {
  $pdo = new PDO($dsn, $username, $password);
  $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

  // 执行 DELETE 语句
  $sql = "DELETE FROM users WHERE id=:id";
  $stmt = $pdo->prepare($sql);
  $stmt->bindParam(':id', $id);
  $stmt->execute();

  echo "删除成功";
} catch(PDOException $e) {
  echo "Error: " . $e->getMessage();
}

// 关闭连接
$pdo = null;

In the above example, we directly hardcoded the deletion condition (id=1). This is not advisable in practical applications, and parameterized queries should be used to bind input variables for deletion operations.

2. Using the ORM framework

ORM (Object-Relational Mapping) is a programming technology that maps tables in a relational database to classes or objects in a programming language. And it realizes the encapsulation, inheritance, polymorphism and other features of object-oriented programming. Using the ORM framework, database operations can be greatly simplified.

The following takes the Laravel framework as an example to show the usage process of the ORM framework. In Laravel, we can define a data model and use the model to perform database operations. For example, we have a user (User) data table, we can define the following data model:

namespace App;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
  protected $table = 'users';
  protected $primaryKey = 'id';
  public $timestamps = false;
}

In the above example, we defined a User model, specified the users data table, and specified the primary key as id. We also turned off the ability to automatically update timestamps ($timestamps=false).

To use the model to delete data, you only need to call the delete method of the model:

$user = User::find(1); // 查询id为1的用户
if ($user) {
  $user->delete(); // 删除该用户
  echo "删除成功";
} else {
  echo "用户不存在";
}

The attributes and methods defined in the model encapsulate some underlying database operations for us, simplifying our code.

3. Using relational databases

Relational databases (such as MySQL, Oracle, SQL Server, etc.) support defining constraints between tables, such as primary keys, foreign keys, etc. When using a relational database, you can delete data by setting "cascade delete" constraints.

Cascade deletion means that when a record in the parent table is deleted, all records in its associated child tables are also deleted. This reduces the amount of code while avoiding data inconsistencies due to program errors or exceptions. For example, we have an Orders data table and an OrderDetails data table. We can set a foreign key in the Order Details table to associate the primary key of the Orders table, and set a "cascade delete" constraint. The code is as follows:

CREATE TABLE Orders (
  order_id INT PRIMARY KEY AUTO_INCREMENT,
  customer_id INT NOT NULL,
  order_date DATE NOT NULL
);

CREATE TABLE OrderDetails (
  order_id INT NOT NULL,
  product_id INT NOT NULL,
  quantity INT NOT NULL,
  CONSTRAINT pk_OrderDetails PRIMARY KEY (order_id, product_id),
  CONSTRAINT fk_OrderDetails_Orders FOREIGN KEY (order_id)
    REFERENCES Orders(order_id)
    ON DELETE CASCADE
);

In the above code, we created two data tables, associated the order details table with the order table, and set the "cascade delete" constraint. When we execute the following SQL statement, we can delete the order and order details at the same time:

DELETE FROM Orders WHERE order_id=1;

In web development, deleting data is an essential operation. The above methods can all realize the function of data deletion. We can choose the most suitable method to meet the needs according to the actual situation.

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