الاتصال بقواعد البيانات (JDBC)

1. تحميل الـ Driver
2. فتح اتصال (Connection)
3. إنشاء كائن الاستعلام (Statement)
4. التنفيذ والاستلام (ResultSet)
5. الإغلاق

import java.sql.*;

String url = "jdbc:mysql://localhost:3306/mydb";
String user = "root";
String password = "secret";

try (Connection conn = DriverManager.getConnection(url, user, password)) {
    System.out.println("تم الاتصال!");
}

try (Connection conn = DriverManager.getConnection(url, user, password);
     Statement stmt = conn.createStatement();
     ResultSet rs = stmt.executeQuery("SELECT id, name, age FROM users")) {

    while (rs.next()) {
        int id = rs.getInt("id");
        String name = rs.getString("name");
        int age = rs.getInt("age");
        System.out.printf("%d - %s (%d)%n", id, name, age);
    }
}

String sql = "SELECT * FROM users WHERE age > ?";

try (PreparedStatement ps = conn.prepareStatement(sql)) {
    ps.setInt(1, 18); // ? الأولى = 18

    try (ResultSet rs = ps.executeQuery()) {
        while (rs.next()) {
            System.out.println(rs.getString("name"));
        }
    }
}

String sql = "INSERT INTO users (name, age) VALUES (?, ?)";

try (PreparedStatement ps = conn.prepareStatement(sql)) {
    ps.setString(1, "سارة");
    ps.setInt(2, 22);
    int rows = ps.executeUpdate(); // عدد الصفوف المتأثرة
    System.out.println("تم إدراج " + rows + " صف");
}

// تحديث
String update = "UPDATE users SET age = ? WHERE name = ?";
try (PreparedStatement ps = conn.prepareStatement(update)) {
    ps.setInt(1, 23);
    ps.setString(2, "سارة");
    ps.executeUpdate();
}

// حذف
String delete = "DELETE FROM users WHERE id = ?";
try (PreparedStatement ps = conn.prepareStatement(delete)) {
    ps.setInt(1, 1);
    ps.executeUpdate();
}

try {
    conn.setAutoCommit(false);

    stmt.executeUpdate("UPDATE accounts SET balance = balance - 100 WHERE id = 1");
    stmt.executeUpdate("UPDATE accounts SET balance = balance + 100 WHERE id = 2");

    conn.commit(); // تأكيد كل التغييرات
} catch (SQLException e) {
    conn.rollback(); // التراجع عن كل شيء
}

// الأفضل: try-with-resources
try (Connection conn = DriverManager.getConnection(url, user, password);
     PreparedStatement ps = conn.prepareStatement(sql)) {

    // كل شيء يُغلق تلقائيًا
}