将__init__函数添加到具有一对一关系的模型会导致Mapper初始化错误

Question

我正在尝试创建一个提交有关Employee的数据的嵌套表单。 Employee有一个Photo与之关联，一对一的关系。以下模型在没有__init__函数的情况下工作，但是当我添加__init__函数时，我得到InvalidRequest异常。为什么__init__的模型会失败？

sqlalchemy.exc.InvalidRequestError: When initializing mapper Mapper|Employee|employee, expression 'Photo' failed to locate a name ("name 'Photo' is not defined"). If this is a class name, consider adding this relationship() to the <class 'blackduckflock.models.Employee'> class after both dependent classes have been defined.

class Employee(db.Model):
    __tablename__ = 'employee'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(200))
    title = db.Column(db.String(200))
    email = db.Column(db.String(200))
    department = db.Column(db.String(200))
    photo = db.relationship('Photo', uselist=False, back_populates='employee', cascade='all, delete')

    def __init__(self, name='', title='', email='', department=''):
        self.name = name
        self.title = title
        self.email = email
        self.department = department
        self.photo = photo

class Photo(db.Model):
   __tablename__ = 'photo'
    id = db.Column(db.Integer, primary_key=True)
    image = db.Column(db.String(200))
    storage_type_field = db.Column(db.String(255), default='')
    bucket_name_field = db.Column(db.String(255), default='')

    employee_id = db.Column(db.Integer, db.ForeignKey('employee.id'))
    employee = db.relationship('Employee', back_populates='photo', cascade='all, delete')

    def __init__(self, image='', storage_type_field='', bucket_name_field='', employee=Employee()):
        self.image = image
        self.storage_type_field = storage_type_field
        self.bucket_name_field = bucket_name_field
        self.employee = employee

Answer 1

这是我的解决方案的答案：

class Photo(db.Model):
    __tablename__ = 'photo'
    id = db.Column(db.Integer, primary_key=True)
    image = db.Column(db.String(200))
    storage_type_field = db.Column(db.String(255), default='')
    bucket_name_field = db.Column(db.String(255), default='')

    employee_id = db.Column(db.Integer, db.ForeignKey('employee.id'))
    employee = db.relationship('Employee', back_populates='photo')

    def __init__(self, image='', storage_type_field='', bucket_name_field=''):
        self.image = image
        self.storage_type_field = storage_type_field
        self.bucket_name_field = bucket_name_field



class Employee(db.Model):
    __tablename__ = 'employee'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(200))
    title = db.Column(db.String(200))
    email = db.Column(db.String(200))
    department = db.Column(db.String(200))
    photo = db.relationship('Photo', uselist=False, back_populates='employee', cascade='all, delete')

    def __init__(self, name='', title='', email='', department='', photo=''):
        self.name = name
        self.title = title
        self.email = email
        self.department = department
        self.photo = Photo()