如何在实际表单验证中使用外键字段

CREATE TABLE Users (
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(255) NOT NULL UNIQUE,
    email VARCHAR(255) NOT NULL UNIQUE
);

CREATE TABLE Orders (
    id INT PRIMARY KEY AUTO_INCREMENT,
    user_id INT,
    product_name VARCHAR(255) NOT NULL,
    FOREIGN KEY (user_id) REFERENCES Users(id)
);

from flask import Flask, request, jsonify
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(255), nullable=False, unique=True)
    email = db.Column(db.String(255), nullable=False, unique=True)

class Order(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    product_name = db.Column(db.String(255), nullable=False)

@app.route('/create_order', methods=['POST'])
def create_order():
    data = request.json
    user_id = data.get('user_id')
    product_name = data.get('product_name')

    # 验证 user_id 是否存在
    user = User.query.get(user_id)
    if not user:
        return jsonify({"error": "User not found"}), 404

    new_order = Order(user_id=user_id, product_name=product_name)
    db.session.add(new_order)
    db.session.commit()

    return jsonify({"message": "Order created successfully"}), 201

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