Php 如何连接两个类从数据库中读取信息？

我不熟悉PHP PDO OOP。我正在尝试使用

\u构造函数创建数据库连接。
这是我的数据库类代码

<?php
// database class
class Database
{
    // database host name
    private $db_host = "localhost";
    // database username
    private $db_user = "root";
    // database name
    private $db_name = "project_crud";
    // database password
    private $db_pass = "";

    public $conn;

    // function for create connection
    public function __construct()
    {
        try {
            $this->conn = new PDO("mysql:host=" . $this->db_host . ";dbname=" . $this->db_name, $this->db_user, $this->db_pass);
            $this->conn->exec("set names utf8");
        } catch (PDOException $e) {
            die("ERROR: Could not connect with database." . $e->getMessage());
        }
        return $this->conn;
    }
}

<?php

class Employees
{
    private $conn;

    private $db_table = "employees";

    public function getConnection()
    {
        $this->conn = $ob ;
    }

    public function readAllEmployee()
    {
        $data   = array();
        $query  = "SELECT * FROM $this->db_table";
        $stmt   = $this->conn->prepare($query);
        $stmt->execute();
        $result = $stmt->fetchAll(PDO::FETCH_ASSOC);

        foreach ($result as $row) {
            $data[] = $row;
        }
        return $data;
    }
}


这里绝对没有理由使用OOP。你拥有的是程序代码。您打开一个到PDO的连接，然后从数据库中获取一些数据。这里没有涉及任何对象

事实上，您的整个代码可以总结在以下几行中（修复后）：

面向对象编程意味着您应该将实体表示为类。例如，
Employee
可以是一个类，然后该类将具有某些方法来对对象执行操作。如果需要，这样的类可以由一个PDO链接组成，尽管您必须考虑您的类是否做了一件事或多件事情（例如从数据库中获取并在雇员对象上执行动作）。
如果您决定实现此类，则可以通过以下方式传递PDO连接：

class Employee
{
    private PDO $pdo;
    public function __construct(PDO $pdo)
    {
        $this->pdo = $pdo;
    }

    public function getByID(int $id): ?array
    {
        $stmt =  $this->pdo->prepare('SELECT * FROM employees WHERE Id=?');
        $stmt->execute([$id]);
        return $stmt->fetch();
    }
}

/**
 * Class representing a real life employee in a company
 */
class Employee {
    private $Id;

    private $Name;

    public function getName(): ?string {
        return $this->Name;
    }
}

// Execute prepared statement to to create a single employee object. 
$stmt = $pdo->query('SELECT Id, Name FROM employees ORDER BY Id LIMIT 1');
$stmt->setFetchMode(PDO::FETCH_CLASS, Employee::class);
$empl = $stmt->fetch();

echo $empl->getName();

// or if you want to fetch by an ID
$stmt = $pdo->prepare('SELECT Id, Name FROM employees WHERE Id=?');
$stmt->execute([1]); // pass ID of the employee
$stmt->setFetchMode(PDO::FETCH_CLASS, Employee::class);
$empl = $stmt->fetch();

echo $empl->getName();

// or if you need to fetch multiple employees
$stmt = $pdo->prepare('SELECT Id, Name FROM employees WHERE Id IN(?,?)');
$stmt->execute([1, 2]); // pass ID of the employee
$stmt->setFetchMode(PDO::FETCH_CLASS, Employee::class);
$employees = $stmt->fetchAll();
foreach ($employees as $empl) {
    var_dump($empl->getName());
}

然后，当您创建此类的实例时，将PDO实例作为参数传递

$emplpyee = new Employee($pdo);
$johndoe = $emplpyee->getByID(42);

现在小心点这仍然不是一个合适的OOP。正如你所看到的，我们班并不是一名雇员。事实上，它充当PDO包装器，用于获取员工。这是PDO已经提供的功能，因此可以通过以下方式对类进行返工：

class Employee
{
    private PDO $pdo;
    public function __construct(PDO $pdo)
    {
        $this->pdo = $pdo;
    }

    public function getByID(int $id): ?array
    {
        $stmt =  $this->pdo->prepare('SELECT * FROM employees WHERE Id=?');
        $stmt->execute([$id]);
        return $stmt->fetch();
    }
}

/**
 * Class representing a real life employee in a company
 */
class Employee {
    private $Id;

    private $Name;

    public function getName(): ?string {
        return $this->Name;
    }
}

// Execute prepared statement to to create a single employee object. 
$stmt = $pdo->query('SELECT Id, Name FROM employees ORDER BY Id LIMIT 1');
$stmt->setFetchMode(PDO::FETCH_CLASS, Employee::class);
$empl = $stmt->fetch();

echo $empl->getName();

// or if you want to fetch by an ID
$stmt = $pdo->prepare('SELECT Id, Name FROM employees WHERE Id=?');
$stmt->execute([1]); // pass ID of the employee
$stmt->setFetchMode(PDO::FETCH_CLASS, Employee::class);
$empl = $stmt->fetch();

echo $empl->getName();

// or if you need to fetch multiple employees
$stmt = $pdo->prepare('SELECT Id, Name FROM employees WHERE Id IN(?,?)');
$stmt->execute([1, 2]); // pass ID of the employee
$stmt->setFetchMode(PDO::FETCH_CLASS, Employee::class);
$employees = $stmt->fetchAll();
foreach ($employees as $empl) {
    var_dump($empl->getName());
}

现在我们有了一个类，它有一些方法并表示单个实体。该类由PDO实例化，PDO创建一个对象并填充其属性。不需要传递PDO或处理类中的依赖项。每个类都有一个单独的职责。
不要尝试捕捉连接错误。除非您打算从错误中恢复，否则不应捕获任何错误。
foreach（$result as$row）
的目的是什么？
Employees
class的目的是什么？这看起来像一个SQL语句将
$db\u host
和其他语句保存为对象的属性有什么意义？你只会使用它们一次，不是吗？你应该创建另一个类，如果你喜欢的话，这是一个特性，它是“数据库连接逻辑”，它可以在你拥有的两个类中“使用”。这个类将用新方法扩展。玩具活动记录。开发商开发过程中不可避免的一步。