'Marshmallow' object has no attribute 'ModelSchema'

Question

Everything looks fine from the documentation but it still gives me this error when I'm running the app:

  File "main.py", line 21, in <module>
    class UserSchema(ma.ModelSchema):
AttributeError: 'Marshmallow' object has no attribute 'ModelSchema'

Everything is imported correctly. The DB is committed. The behavior is the same on pipenv and venv.

Am I missing something?

from flask import Flask, jsonify
from flask_sqlalchemy import SQLAlchemy 
from flask_marshmallow import Marshmallow

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

db  = SQLAlchemy(app)
ma = Marshmallow(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))

class Item(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    item_name = db.Column(db.String(50))
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    user = db.relationship('User', backref='items')

class UserSchema(ma.ModelSchema):
    class Meta:
        model = User 
        
class ItemSchema(ma.ModelSchema):
    class Meta:
        model = Item

@app.route('/')
def index():
    users = User.query.all()
    user_schema = UserSchema(many=True)
    output = user_schema.dump(users).data
    return jsonify({'user': output})

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

Answer 1

Conf.py

from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow

db = SQLAlchemy(app)
ma = Marshmallow(app) 

# flask-marshmallow<0.12.0

class UserSchema(ma.ModelSchema):
      class Meta:
            model = User

# flask-marshmallow>=0.12.0 (recommended)

from conf import ma
class UserSchema(ma.SQLAlchemyAutoSchema):
      class Meta:
            model = User
            load_instance = True

# flask-marshmallow>=0.12.0 (not recommended)

from marshmallow_sqlalchemy import ModelSchema
class UserSchema(ModelSchema):
      class Meta:
            model = User
            sql_session = db.session