Question

我有3个sqlalchemy模型设置，它们都是一对多的关系。用户模型包含许多任务模型，任务模型包含许多子任务模型。当我执行test_script.py时，出现错误sqlalchemy.orm.exc.UnmappedInstanceError: Class 'builtins.NoneType' is not mapped。

我已经阅读并尝试了每个模块的一些不同关系。我的目标是能够在用户和任务模型中包含其正确子代的列表。我最终想访问列表项，例如user_x.task[3].subtask[1]

这是代码，（模型，脚本，错误）

模型

class User(Base):
    """ User Model for storing user related details """
    __tablename__ = 'Users'

    id = Column(Integer, primary_key=True, autoincrement=True, nullable=False)
    username = Column(String(255), nullable=False)
    password_hash = Column(String(128), nullable=False)
    email = Column(String(255), nullable=False, unique=True)
    created_date = Column(DateTime, default=datetime.utcnow)

    tasks = relationship(Task, backref=backref("Users", uselist=False))

    def __init__(self, username: str, password_hash: str, email: str):
        self.username = username
        self.password_hash = password_hash
        self.email = email



class Task(Base):
    """ Task Model for storing task related details """
    __tablename__ = 'Tasks'

    id = Column(Integer, primary_key=True, autoincrement=True, nullable=False)
    title = Column(String(255), nullable=False)
    folder_name = Column(String(255), nullable=True)
    due_date = Column(DateTime, nullable=True)
    starred = Column(Boolean, default=False)
    completed = Column(Boolean, default=False)
    note = Column(String, nullable=True)
    created_date = Column(DateTime, default=datetime.utcnow)
    user_id = Column(Integer, ForeignKey('Users.id'))

    subtasks = relationship(Subtask, backref=backref("Tasks", uselist=False))

    def __init__(self, title: str, **kwargs):
        self.title = title
        self.folder_name = kwargs.get('folder_name', None)
        self.due_date = kwargs.get('due_date', None)
        self.starred = kwargs.get('starred', False)
        self.completed = kwargs.get('completed', False)
        self.note = kwargs.get('note', None)



class Subtask(Base):
    """ Subtask Model for storing subtask related details """
    __tablename__ = 'Subtasks'

    id = Column(Integer, primary_key=True, nullable=False, autoincrement=True)
    title = Column(String(255), nullable=False)
    completed = Column(Boolean, default=False)
    task_id = Column(Integer, ForeignKey('Tasks.id'))

    def __init__(self, title: str, **kwargs):
        self.title = title
        self.completed = kwargs.get('completed', False)

test_script.py

session1 = create_session()

user1 = User(
    username="Stephen",
    password_hash="p-hash",
    email="stephen@gmail.com"
).tasks.append(
    Task(
        title='Delete Me',
        folder_name='Folder 1'
    ).subtasks.append(
        Subtask(
            title='Delete Me 2'
        )
    )
)

session1.add(user1)

session1.commit()
session1.close()

错误消息

/Users/StephenCollins/Respositories/pycharm_workspace/Personal/BusyAPI_v1/venv/bin/python /Users/StephenCollins/Respositories/pycharm_workspace/Personal/BusyAPI_v1/tests/test_script.py
Traceback (most recent call last):
  File "/Users/StephenCollins/Respositories/pycharm_workspace/Personal/BusyAPI_v1/venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1943, in add
    state = attributes.instance_state(instance)
AttributeError: 'NoneType' object has no attribute '_sa_instance_state'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/StephenCollins/Respositories/pycharm_workspace/Personal/BusyAPI_v1/tests/test_script.py", line 24, in <module>
    session1.add(user1)
  File "/Users/StephenCollins/Respositories/pycharm_workspace/Personal/BusyAPI_v1/venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1945, in add
    raise exc.UnmappedInstanceError(instance)
sqlalchemy.orm.exc.UnmappedInstanceError: Class 'builtins.NoneType' is not mapped

希望我已经接近了，但是如果我完全朝错误的方向前进，请告诉我。我在以前的实习中使用过Hibernate，但是我在python，sqlalchemy和mysql中是自学的（最好的一种）。

Answer 1

在Python中就地改变对象的方法通常返回None。您分配的表达式链创建了模型对象，访问了一个关系属性，并附加到该属性上，该属性返回None。拆分操作：

user1 = User(
    username="Stephen",
    password_hash="p-hash",
    email="stephen@gmail.com"
)

task1 = Task(
    title='Delete Me',
    folder_name='Folder 1'
)

task1.subtasks.append(
    Subtask(
        title='Delete Me 2'
    )
)

user1.tasks.append(task1)

Answer 2

由于您正在重载__init__，因此有必要在模型中初始化超类：

class User(Base):
    def __init__(self, username: str, password_hash: str, email: str):
        // Initialize self
        [...]

        // Initialize base class
        super(User, self).__init__()

请注意，通常不需要定义自己的构造函数__init__，因为声明性基类已经定义了一个构造函数，该构造函数采用与模型属性相对应的**kwargs。

sqlalchemy.orm.exc.UnmappedInstanceError：未映射类“ builtins.NoneType”

2 个答案: