注册时Method Not Allowed The method is not allowed for the requested URL.修复问题，给完整代码

从提供的代码来看，`register`路由已经支持了 `GET` 和 `POST` 方法。如果出现 "Method Not Allowed" 错误，通常是因为请求方法与路由定义的方法不匹配。以下是一些可能的原因和解决方案：

1. **检查表单提交方式**：确保前端表单的提交方法是 `POST`，而不是 `GET`。
2. **检查URL路径**：确保访问的URL路径正确，并且没有拼写错误。

以下是完整的代码，确保所有部分都正确无误：

from flask import Flask, render_template, request, redirect, url_for, flash, session
import mysql.connector
import bcrypt
import logging

app = Flask(__name__)
app.secret_key = 'your_secret_key'

# 配置日志
logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')

# 数据库连接
def connect_db():
    conn = mysql.connector.connect(
        host='localhost',
        port=3306,
        user='root',
        password='123456',
        database='pet_weight_management'
    )
    return conn

# 初始化数据库
def init_db():
    conn = connect_db()
    cursor = conn.cursor()
    cursor.execute('''
    CREATE TABLE IF NOT EXISTS users (
        id INT AUTO_INCREMENT PRIMARY KEY,
        username VARCHAR(255) UNIQUE NOT NULL,
        password VARCHAR(255) NOT NULL
    )
    ''')
    cursor.execute('''
    CREATE TABLE IF NOT EXISTS pets (
        id INT AUTO_INCREMENT PRIMARY KEY,
        user_id INT NOT NULL,
        pet_name VARCHAR(255) NOT NULL,
        FOREIGN KEY (user_id) REFERENCES users (id) ON DELETE CASCADE
    )
    ''')
    cursor.execute('''
    CREATE TABLE IF NOT EXISTS pet_weights (
        id INT AUTO_INCREMENT PRIMARY KEY,
        pet_id INT NOT NULL,
        weight DECIMAL(10, 2) NOT NULL,
        recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
        FOREIGN KEY (pet_id) REFERENCES pets (id) ON DELETE CASCADE
    )
    ''')
    conn.commit()
    conn.close()

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/register', methods=['GET', 'POST'])
def register():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        conn = connect_db()
        cursor = conn.cursor()
        hashed_password = bcrypt.hashpw(password.encode('utf-8'), bcrypt.gensalt())
        try:
            cursor.execute('INSERT INTO users (username, password) VALUES (%s, %s)', (username, hashed_password))
            conn.commit()
            flash("注册成功！", 'success')
            logging.info("用户 %s 注册成功！", username)
            return redirect(url_for('login'))
        except mysql.connector.IntegrityError:
            flash("用户名已存在！", 'warning')
            logging.warning("用户名 %s 已存在！", username)
        finally:
            conn.close()
    return render_template('register.html')

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        conn = connect_db()
        cursor = conn.cursor()
        cursor.execute('SELECT id, password FROM users WHERE username = %s', (username,))
        result = cursor.fetchone()
        if result and bcrypt.checkpw(password.encode('utf-8'), result[1]):
            session['user_id'] = result[0]
            flash("登录成功！", 'success')
            logging.info("用户 %s 登录成功！", username)
            return redirect(url_for('dashboard'))
        else:
            flash("用户名或密码错误！", 'danger')
            logging.warning("用户名或密码错误！")
        conn.close()
    return render_template('login.html')

@app.route('/logout')
def logout():
    session.pop('user_id', None)
    flash("已退出登录。", 'info')
    logging.info("已退出登录。")
    return redirect(url_for('index'))

@app.route('/dashboard')
def dashboard():
    if 'user_id' not in session:
        return redirect(url_for('login'))
    user_id = session['user_id']
    conn = connect_db()
    cursor = conn.cursor()
    cursor.execute('SELECT id, pet_name FROM pets WHERE user_id = %s', (user_id,))
    pets = cursor.fetchall()
    conn.close()
    return render_template('dashboard.html', pets=pets)

@app.route('/add_pet', methods=['GET', 'POST'])
def add_pet():
    if 'user_id' not in session:
        return redirect(url_for('login'))
    if request.method == 'POST':
        user_id = session['user_id']
        pet_name = request.form['pet_name']
        weight = float(request.form['weight'])
        conn = connect_db()
        cursor = conn.cursor()
        cursor.execute('INSERT INTO pets (user_id, pet_name) VALUES (%s, %s)', (user_id, pet_name))
        pet_id = cursor.lastrowid
        cursor.execute('INSERT INTO pet_weights (pet_id, weight) VALUES (%s, %s)', (pet_id, weight))
        conn.commit()
        flash("宠物添加成功，初始体重为 %.2f kg" % weight, 'success')
        logging.info("宠物 %s 添加成功，初始体重为 %.2f kg", pet_name, weight)
        conn.close()
        return redirect(url_for('dashboard'))
    return render_template('add_pet.html')

@app.route('/view_pet/<int:pet_id>')
def view_pet(pet_id):
    if 'user_id' not in session:
        return redirect(url_for('login'))
    conn = connect_db()
    cursor = conn.cursor()
    cursor.execute('SELECT pet_name FROM pets WHERE id = %s', (pet_id,))
    pet = cursor.fetchone()
    if not pet:
        flash("宠物不存在！", 'warning')
        logging.warning("宠物不存在！")
        return redirect(url_for('dashboard'))
    cursor.execute('SELECT weight, recorded_at FROM pet_weights WHERE pet_id = %s ORDER BY recorded_at', (pet_id,))
    weights = cursor.fetchall()
    conn.close()
    return render_template('view_pet.html', pet=pet, weights=weights)

@app.route('/update_pet_weight/<int:pet_id>', methods=['GET', 'POST'])
def update_pet_weight(pet_id):
    if 'user_id' not in session:
        return redirect(url_for('login'))
    conn = connect_db()
    cursor = conn.cursor()
    # 获取当前宠物的所有体重记录
    cursor.execute('SELECT weight, recorded_at FROM pet_weights WHERE pet_id = %s ORDER BY recorded_at DESC', (pet_id,))
    weights = cursor.fetchall()
    if request.method == 'POST':
        weight = float(request.form['weight'])
        cursor.execute('INSERT INTO pet_weights (pet_id, weight) VALUES (%s, %s)', (pet_id, weight))
        conn.commit()
        flash("宠物体重更新成功！", 'success')
        logging.info("宠物体重更新成功！")
        conn.close()
        return redirect(url_for('view_pet', pet_id=pet_id))
    conn.close()
    return render_template('update_pet_weight.html', pet_id=pet_id, weights=weights)

@app.route('/delete_account', methods=['GET', 'POST'])
def delete_account():
    if 'user_id' not in session:
        return redirect(url_for('login'))
    if request.method == 'POST':
        user_id = session['user_id']
        conn = connect_db()
        cursor = conn.cursor()
        try:
            # 删除宠物的体重记录
            cursor.execute('DELETE FROM pet_weights WHERE pet_id IN (SELECT id FROM pets WHERE user_id = %s)', (user_id,))
            # 删除宠物信息
            cursor.execute('DELETE FROM pets WHERE user_id = %s', (user_id,))
            # 删除用户信息
            cursor.execute('DELETE FROM users WHERE id = %s', (user_id,))
            conn.commit()
            session.pop('user_id', None)
            flash("账号已注销。", 'success')
            logging.info("用户 %s 账号已注销。", user_id)
        except Exception as e:
            flash("注销账号失败: %s" % str(e), 'danger')
            logging.error("注销账号失败: %s", str(e))
        finally:
            conn.close()
        return redirect(url_for('index'))
    return render_template('delete_account.html')

if __name__ == '__main__':
    init_db()
    app.run(debug=True)

### 前端模板示例 (`register.html`)
确保前端表单使用 `POST` 方法提交：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>注册</title>
</head>
<body>
    <h1>注册</h1>
    <form action="{{ url_for('register') }}" method="post">
        <label for="username">用户名:</label>
        <input type="text" id="username" name="username" required><br><br>
        <label for="password">密码:</label>
        <input type="password" id="password" name="password" required><br><br>
        <button type="submit">注册</button>
    </form>
</body>
</html>

通过以上步骤，可以确保注册功能正常工作，避免 "Method Not Allowed" 错误。