Flask-Restless & Marshmallow：“dict”对象没有属性“_sa_instance_state”

Posted 2023-02-27

【中文标题】Flask-Restless & Marshmallow：“dict”对象没有属性“_sa_instance_state”

【英文标题】：Flask-Restless & Marshmallow: 'dict' object has no attribute '_sa_instance_state'

【发布时间】：2016-11-14 15:14:39

【问题描述】：

我正在使用 Flask-Restless、Flask-SQLAlchemy 和 Marshmallow 开发一个基本的 CRUD JSON REST API。

我在使用这种库组合时遇到了问题，但只有当我使用 Marshmallow 启用反序列化时。

我已经广泛地用谷歌搜索了这个错误，但是我只在使用数据库关系时发现了类似的问题，而我没有。

我一直在从我的应用程序中删除尽可能多的代码，但仍然遇到相同的错误。以下代码块是本地运行的 1:1。

models.py：

from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()

class Case(db.Model):
    __tablename__ = 'case'
    id = db.Column(db.Integer, primary_key=True)
    amount = db.Column(db.Integer, nullable=False)

serializers.py：

from marshmallow import Schema


class CaseSchema(Schema):
    pass  # for simplicity - nothing works

case_schema = CaseSchema()


def case_serializer(instance):
    return case_schema.dump(instance).data


def case_deserializer(data):
    return case_schema.load(data).data

ma​​in.py:

from flask import Flask
import flask_restless

import models
import serializers

app = Flask(__name__)
app.config['DEBUG'] = True    
models.db.init_app(app)


def init_db():
    with app.app_context():
        models.db.create_all()


def init_api():
    init_db()

    with app.app_context():
        api_manager = flask_restless.APIManager(app, flask_sqlalchemy_db=models.db)
        api_manager.create_api(models.Case, methods=['GET', 'POST', 'PUT'],
                               serializer=serializers.case_serializer,
                               deserializer=serializers.case_deserializer)  # <- stuff breaks when enabling this line


if __name__ == "__main__":
    init_db()
    init_api()
    app.run()

tests.py：

import json
import os
import myapp
import unittest
import tempfile


with myapp.app.app_context():
    myapp.init_api()


class MyappTestCase(unittest.TestCase):
    def setUp(self):
        self.db_fd, myapp.app.config['DATABASE'] = tempfile.mkstemp()
        myapp.app.config['TESTING'] = True
        self.app = myapp.app.test_client()

    def tearDown(self):
        os.close(self.db_fd)
        os.unlink(myapp.app.config['DATABASE'])

    def test_create_case(self):
        msg = 
            "amount": 1038,
        

        post_response = self.app.post("/api/case", data=json.dumps(msg),
                                      content_type="application/json")
        assert post_response.status_code == 201

if __name__ == '__main__':
    unittest.main()

正在使用的版本：

Flask==0.11
Flask-SQLAlchemy==2.1
Flask-Restless==0.17.0
mysqlclient==1.3.7
SQLAlchemy-Utils==0.32.8
marshmallow==2.9.0

最后，运行测试时的完整堆栈跟踪：

======================================================================
ERROR: test_create_case (__main__.myappTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/sqlalchemy/orm/session.py", line 1584, in add
    state = attributes.instance_state(instance)
AttributeError: 'dict' object has no attribute '_sa_instance_state'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "myapp_tests.py", line 37, in test_create_case
    content_type="application/json")
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/werkzeug/test.py", line 788, in post
    return self.open(*args, **kw)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/testing.py", line 113, in open
    follow_redirects=follow_redirects)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/werkzeug/test.py", line 751, in open
    response = self.run_wsgi_app(environ, buffered=buffered)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/werkzeug/test.py", line 668, in run_wsgi_app
    rv = run_wsgi_app(self.application, environ, buffered=buffered)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/werkzeug/test.py", line 871, in run_wsgi_app
    app_rv = app(environ, start_response)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 2000, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 1991, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 1567, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 1988, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 1641, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 1544, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 1639, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/app.py", line 1625, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask_restless/views.py", line 157, in decorator
    return func(*args, **kw)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/mimerender.py", line 244, in wrapper
    result = target(*args, **kwargs)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/views.py", line 84, in view
    return self.dispatch_request(*args, **kwargs)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask/views.py", line 149, in dispatch_request
    return meth(*args, **kwargs)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask_restless/views.py", line 189, in wrapped
    return func(*args, **kw)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/flask_restless/views.py", line 1449, in post
    self.session.add(instance)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/sqlalchemy/orm/scoping.py", line 157, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.5/site-packages/sqlalchemy/orm/session.py", line 1586, in add
    raise exc.UnmappedInstanceError(instance)
sqlalchemy.orm.exc.UnmappedInstanceError: Class 'builtins.dict' is not mapped

【参考方案1】：

原来我必须在模型定义中添加__tablename__ 并扩展架构：

class CaseSchema(Schema):
    [...]

    @post_load
    def make_case(self, data):
        return Case(**data)