Using Object-Oriented PHP with a database class is an excellent choice for modularity, reusability, and clean code. Below is a detailed explanation and a full implementation covering CRUD (Create, Read, Update, Delete) operations, along with WHERE, ORDER BY, and other conditions.

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Step 1: Create a Database Class

Here’s a simple and reusable Database class:

<?php
class Database {
    private $conn;

    public function __construct($host, $user, $pass, $dbname) {
        $this->conn = new mysqli($host, $user, $pass, $dbname);

        // Check for connection errors
        if ($this->conn->connect_error) {
            die("Connection failed: " . $this->conn->connect_error);
        }
    }

    // INSERT Method
    public function insert($table, $data) {
        $columns = implode(", ", array_keys($data));
        $values = implode("', '", array_map([$this->conn, 'real_escape_string'], array_values($data)));
        $sql = "INSERT INTO $table ($columns) VALUES ('$values')";
        return $this->conn->query($sql);
    }

    // SELECT Method
    public function select($table, $columns = "*", $conditions = "") {
        $sql = "SELECT $columns FROM $table $conditions";
        $result = $this->conn->query($sql);

        if ($result->num_rows > 0) {
            return $result->fetch_all(MYSQLI_ASSOC);
        }
        return [];
    }

    // UPDATE Method
    public function update($table, $data, $conditions) {
        $set = [];
        foreach ($data as $column => $value) {
            $set[] = "$column = '" . $this->conn->real_escape_string($value) . "'";
        }
        $setQuery = implode(", ", $set);
        $sql = "UPDATE $table SET $setQuery $conditions";
        return $this->conn->query($sql);
    }

    // DELETE Method
    public function delete($table, $conditions) {
        $sql = "DELETE FROM $table $conditions";
        return $this->conn->query($sql);
    }

    // Close the connection
    public function close() {
        $this->conn->close();
    }
}
?>

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Step 2: Use the Database Class

1. Inserting Data

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

$data = [
    'name' => 'John Doe',
    'email' => 'john@example.com',
    'age' => 30
];
if ($db->insert("users", $data)) {
    echo "Data inserted successfully!";
} else {
    echo "Error: " . $db->conn->error;
}

---

2. Selecting Data with Conditions

// Fetch all records
$users = $db->select("users");
print_r($users);

// Fetch specific records with WHERE and ORDER BY
$conditions = "WHERE age > 20 ORDER BY name ASC";
$users = $db->select("users", "*", $conditions);

foreach ($users as $user) {
    echo $user['name'] . " - " . $user['email'] . "<br>";
}

---

3. Updating Data

$data = [
    'email' => 'newemail@example.com',
    'age' => 35
];
$conditions = "WHERE name = 'John Doe'";
if ($db->update("users", $data, $conditions)) {
    echo "Data updated successfully!";
} else {
    echo "Error: " . $db->conn->error;
}

---

4. Deleting Data

$conditions = "WHERE age < 18";
if ($db->delete("users", $conditions)) {
    echo "Records deleted successfully!";
} else {
    echo "Error: " . $db->conn->error;
}

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Step 3: Enhancing the Class

To make the class more robust, you can:

1. Add Error Handling:

   if (!$this->conn->query($sql)) {
       throw new Exception("Query Error: " . $this->conn->error);
   }
   

2. Add Pagination Support:

   public function selectWithLimit($table, $columns = "*", $conditions = "", $limit = 10, $offset = 0) {
       $sql = "SELECT $columns FROM $table $conditions LIMIT $limit OFFSET $offset";
       // Same fetch logic as the select method
   }
   

3. Transaction Support:

   public function beginTransaction() {
       $this->conn->begin_transaction();
   }
   
   public function commit() {
       $this->conn->commit();
   }
   
   public function rollback() {
       $this->conn->rollback();
   }
   

4. Prepared Statements for Security: (For select, update, delete)

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Step 4: Full Example

Here’s how you might combine everything in one usage example:

<?php
$db = new Database("localhost", "username", "password", "database");

// Insert data
$db->insert("users", ['name' => 'Alice', 'email' => 'alice@example.com', 'age' => 25]);

// Fetch data
$users = $db->select("users", "*", "WHERE age > 20 ORDER BY age DESC");

// Update data
$db->update("users", ['email' => 'updated@example.com'], "WHERE name = 'Alice'");

// Delete data
$db->delete("users", "WHERE age < 18");

// Close the connection
$db->close();
?>

This setup allows for easy and modular database operations in your PHP projects! Let me know if you need further clarification or additional features.