漠然としたFlask-SQLAlchemyエラー：「AttributeError：mapper」

さて、かなり基本的なモデル定義のようです。私は最初にどこから始めるべきか分からない。私が実際にチェックすると思う唯一のことは、テーブルが存在することです.db.create_all（）関数はモデル定義に基づいてテーブルを作成できるようです。漠然としたFlask-SQLAlchemyエラー：「AttributeError：mapper」

エラーはあまりにも曖昧で、見た目の手がかりを与えません。基本的にエラーは何を意味しますか？ Settingクラスがマップに失敗していますか？ mapperという名前の属性はありませんか？ここで

コードです：

# the model 
class Setting(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    name = db.Column(db.String, nullable=False) 
    description = db.Column(db.String) 
    value_type = db.Column(db.String) 
    value = db.Column(db.String, nullable=False) 

    def get(name): 
     setting = db.session.query(Setting).filter(
      Setting.name == name).first() 

     if setting.value_type == 'int': 
      return int(setting.value) 

     if setting.value_type == 'float': 
      return float(setting.value) 

    def all_settings(): 
     return {s.name: s.value for s in db.session.query(Setting).all()} 

# what's causing the exception: 
def load_default_settings(): 
    print("Loading default settings") 

    # in case it helps: 
    print(Setting.__dict__) 
    # {'__mapper__': <Mapper at 0x7f5633523278; Setting>, 'name': <sqlalchemy.orm.attributes.InstrumentedAttribute object at 0x7f563356eca8>, '__table__': Table('setting', MetaData(bind=None), Column('id', Integer(), table=<setting>, primary_key=True, nullable=False), Column('name', String(), table=<setting>, nullable=False), Column('description', String(), table=<setting>), Column('value_type', String(), table=<setting>), Column('value', String(), table=<setting>, nullable=False), schema=None), '__doc__': None, '_cached_tablename': 'setting', 'description': <sqlalchemy.orm.attributes.InstrumentedAttribute object at 0x7f563356ed58>, 'get': <function Setting.get at 0x7f5633581f28>, '__init__': <function __init__ at 0x7f5636806400>, 'id': <sqlalchemy.orm.attributes.InstrumentedAttribute object at 0x7f563356ebf8>, 'value': <sqlalchemy.orm.attributes.InstrumentedAttribute object at 0x7f563356eeb8>, 'value_type': <sqlalchemy.orm.attributes.InstrumentedAttribute object at 0x7f563356ee08>, 'all_settings': <function Setting.all_settings at 0x7f563350c048>, '__module__': 'gg.settings', '_sa_class_manager': <ClassManager of <class 'gg.settings.Setting'> at 7f563350dd68>} 

    for name, details in SETTINGS.items(): 
     # calling the Setting constructor below causes the exception 
     setting = Setting(
      name=name, 
      description=details['description'], 
      value=details['value'], 
      value_type=details['value_type']) 
     db.session.add(setting) 

    db.session.commit() 

# traceback 
Traceback (most recent call last): 
    File "main.py", line 5, in <module> 
    import gg.cli 
    File "/home/nicken/freelance/project/gg/cli/__init__.py", line 75, in <module> 
    reset_all() 
    File "/home/nicken/freelance/project/gg/cli/__init__.py", line 55, in reset_all 
    load_initial_data() 
    File "/home/nicken/freelance/project/gg/cli/__init__.py", line 45, in load_initial_data 
    load_default_settings() 
    File "/home/nicken/freelance/project/gg/settings.py", line 84, in load_default_settings 
    value_type=details['value_type'])) 
    File "<string>", line 2, in __init__ 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/instrumentation.py", line 347, in _new_state_if_none 
    state = self._state_constructor(instance, self) 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/util/langhelpers.py", line 764, in __get__ 
    obj.__dict__[self.__name__] = result = self.fget(obj) 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/instrumentation.py", line 177, in _state_constructor 
    self.dispatch.first_init(self, self.class_) 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/event/attr.py", line 256, in __call__ 
    fn(*args, **kw) 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/mapper.py", line 2976, in _event_on_first_init 
    configure_mappers() 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/mapper.py", line 2872, in configure_mappers 
    mapper._post_configure_properties() 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/mapper.py", line 1765, in _post_configure_properties 
    prop.init() 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/interfaces.py", line 184, in init 
    self.do_init() 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/relationships.py", line 1652, in do_init 
    self._process_dependent_arguments() 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/orm/relationships.py", line 1709, in _process_dependent_arguments 
    self.target = self.mapper.mapped_table 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/util/langhelpers.py", line 850, in __getattr__ 
    return self._fallback_getattr(key) 
    File "/home/nicken/freelance/project/lib/python3.4/site-packages/sqlalchemy/util/langhelpers.py", line 828, in _fallback_getattr 
    raise AttributeError(key) 
AttributeError: mapper

私はまた、シェル内のコードをチェックしてみました...動作しているようです。

>>> from gg.app import db 
>>> from gg.settings import Setting 
>>> setting = Setting(name='test', description='test...', value='20', value_type='int') 
>>> db.session.add(setting) 
>>> db.session.commit() 
>>> db.session.query(Setting).all() 
[<gg.settings.Setting object at 0x7f5596d11fd0>]

出典

2017-06-22 Blaine Lafreniere

[Python SqlAlchemy - AttributeError：mapper]の可能な複製（https://stackoverflow.com/questions/45534903/python-sqlalchemy-attributeerror-mapper） –