如何在flask_sqlalchemy中使用PostgreSQL的"INSERT...ON CONFLICT“(UPSERT)特性？

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(50), unique=True)
    email = db.Column(db.String(100), unique=True)

from flask import Flask

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://username:password@host:port/database_name'
db.init_app(app)

from sqlalchemy import text

query = text("""
    INSERT INTO users (username, email)
    VALUES (:username, :email)
    ON CONFLICT (username) DO UPDATE SET email = EXCLUDED.email
""")
params = {'username': 'john', 'email': 'john@example.com'}
db.session.execute(query, params)
db.session.commit()