flask怎么连接mysql数据库

你可以使用 Flask 中的 SQLAlchemy 扩展来连接 MySQL 数据库。首先在 Flask 中安装 SQLAlchemy 扩展：

pip install flask-sqlalchemy

然后在 Flask 项目中创建一个 app.py 文件，并在其中添加以下代码：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://username:password@host:port/database'
db = SQLAlchemy(app)

@app.route('/')
def index():
    return 'Hello, world!'

if __name__ == '__main__':
    app.run()

在上面的代码中，将 `username`、`password`、`host`、`port`、`database` 替换成你自己的 MySQL 数据库信息。然后运行 Flask 项目，即可连接到 MySQL 数据库。

相关问题

改为使用mysql数据库

要将现有的Flask应用程序从SQLite迁移到MySQL，需要进行以下步骤：

1. **安装MySQL驱动**：首先，确保安装了MySQL的Python驱动程序 `mysql-connector-python` 或者 `pymysql`。可以使用以下命令安装：

   pip install mysql-connector-python

2. **修改数据库连接配置**：将原有的SQLite数据库连接代码更改为MySQL的连接代码。

3. **调整SQL语句**：虽然大多数SQL语句在SQLite和MySQL之间是兼容的，但某些语法可能会有所不同，需要进行相应的调整。

以下是修改后的代码示例：

### 修改后的代码

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',
        user='your_username',
        password='your_password',
        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 FLOAT 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)

### 关键点总结
1. **数据库连接**：使用 `mysql.connector` 连接到MySQL数据库。
2. **SQL语句**：调整SQL语句以适应MySQL的语法（例如，使用 `%s` 作为占位符）。
3. **初始化数据库**：创建表时使用MySQL的语法。

通过以上步骤，你可以将现有的Flask应用从SQLite迁移到MySQL。