feat: 实现成绩管理系统核心功能

添加响应工具、错误处理中间件和数据库模型
创建用户、学生、课程和成绩相关服务
实现管理员、教师和学生控制器的基本功能
重构路由处理并优化数据库查询

backend/config/database.js

@@ -11,54 +11,32 @@ const pool = mysql.createPool({
   queueLimit: 0
 });
 
-// 测试数据库连接
-async function testConnection() {
-  try {
-    const connection = await pool.getConnection();
-    console.log('数据库连接成功');
-    connection.release();
-    return true;
-  } catch (error) {
-    console.error('数据库连接失败:', error.message);
-    return false;
-  }
-}
-
-// 执行查询
-async function query(sql, params) {
-  try {
-    const [rows] = await pool.execute(sql, params);
-    return rows;
-  } catch (error) {
-    console.error('数据库查询错误:', error.message);
-    throw error;
-  }
-}
-
-// 执行事务
-async function executeTransaction(operations) {
-  const connection = await pool.getConnection();
-  try {
-    await connection.beginTransaction();
-    
-    for (const operation of operations) {
-      await connection.execute(operation.sql, operation.params);
+// 封装基本查询方法
+const query = async (sql, params) => {
+    try {
+        const [rows] = await pool.execute(sql, params);
+        return rows;
+    } catch (error) {
+        console.error('Database query error:', error);
+        throw error;
     }
-    
-    await connection.commit();
-    console.log('事务执行成功');
-  } catch (error) {
-    await connection.rollback();
-    console.error('事务执行失败:', error.message);
-    throw error;
-  } finally {
-    connection.release();
-  }
-}
+};
+
+// 测试连接
+const testConnection = async () => {
+    try {
+        const connection = await pool.getConnection();
+        console.log('数据库连接成功');
+        connection.release();
+        return true;
+    } catch (error) {
+        console.error('数据库连接失败:', error.message);
+        return false;
+    }
+};
 
 module.exports = {
-  pool,
-  query,
-  executeTransaction,
-  testConnection
+    pool,
+    query,
+    testConnection
 };