Flask-SQLAlchemy mixin與__table_args__中的CheckConstraint結果有錯誤

Question

我試圖在基類中創建具有單個CheckConstraint的基本模型。當我將基類混入flask-sqlalchemy模型並嘗試使用它時，我得到「無法將未命名列添加到列集合」。

我試圖用不同的方式來聲明這個CheckConstraint ，但都導致了這個相同的錯誤。任何想法是什麼造成這種情況？

from sqlalchemy.ext.declarative import declared_attr 
from myproject.db import db 


class FilteringMixin(db.Model): 
    __abstract__ = True 

    FILTER_TYPES = { 
     'whitelist': 0, 
     'blacklist': 1, 
    } 

    @declared_attr.cascading 
    def filter_type(cls): 
     return db.Column(db.SmallInteger, nullable=False, 
         default=cls.FILTER_TYPES['whitelist']) 

    @declared_attr.cascading 
    def __table_args__(cls): 
     return (
       db.CheckConstraint(cls.filter_type.in_(cls.FILTER_TYPES.values())), 
     ) 


class FilteredConnectionType(FilteringMixin, db.Model): 
    CONNECTION_TYPES = { 
     'wifi': 0, 
     'cellular': 1, 
    } 

    __tablename__ = 'filtered_connection_types' 

    id = db.Column(db.BigInteger, primary_key=True) 

    connection_type = db.Column(db.SmallInteger, nullable=False, 
           default=CONNECTION_TYPES['cellular']) 

    @declared_attr.cascading 
    def __table_args__(cls): 
     return (
      db.CheckConstraint(cls.connection_type.in_(cls.CONNECTION_TYPES.values())), 
     ) + FilteringMixin.__table_args__ 

之後，嘗試使用它我得到：

python manage.py shell 
~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py:173: SAWarning: Unmanaged access of declarative attribute __table_args__ from non-mapped class FilteringMixin 
    (desc.fget.__name__, cls.__name__)) 
~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py:173: SAWarning: Unmanaged access of declarative attribute filter_type from non-mapped class FilteringMixin 
    (desc.fget.__name__, cls.__name__)) 
Traceback (most recent call last): 
    File "manage.py", line 4, in <module> 
    from myproject import create_app, environments, scripts 
    File "~/myuser/myproject/myproject/__init__.py", line 9, in <module> 
    import models 
    File "~/myuser/myproject/myproject/models/__init__.py", line 13, in <module> 
    from .filtering_implemented import FilteredConnectionType 
    File "~/myuser/myproject/myproject/models/filtering_implemented.py", line 6, in <module> 
    class FilteredConnectionType(FilteringMixin, db.Model): 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 609, in __init__ 
    DeclarativeMeta.__init__(self, name, bases, d) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py", line 55, in __init__ 
    _as_declarative(cls, classname, cls.__dict__) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 88, in _as_declarative 
    _MapperConfig.setup_mapping(cls, classname, dict_) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 103, in setup_mapping 
    cfg_cls(cls_, classname, dict_) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 131, in __init__ 
    self._setup_table() 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 394, in _setup_table 
    **table_kw) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 416, in __new__ 
    metadata._remove_table(name, schema) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__ 
    compat.reraise(exc_type, exc_value, exc_tb) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 411, in __new__ 
    table._init(name, metadata, *args, **kw) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 488, in _init 
    self._init_items(*args) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 72, in _init_items 
    item._set_parent_with_dispatch(self) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/base.py", line 433, in _set_parent_with_dispatch 
    self._set_parent(parent) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 2553, in _set_parent 
    ColumnCollectionMixin._set_parent(self, table) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 2521, in _set_parent 
    self.columns.add(col) 
    File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/base.py", line 509, in add 
    "Can't add unnamed column to column collection") 
sqlalchemy.exc.ArgumentError: Can't add unnamed column to column collection 

Answer 1

我認爲真正的問題是在兩個警告在錯誤輸出的頂部突出顯示：

.../api.py:173: SAWarning: Unmanaged access of declarative attribute __table_args__ from non-mapped class FilteringMixin 
    (desc.fget.__name__, cls.__name__)) 

而且，據我所知，它是由FilteringMixin.__table_args__的使用引起的，修復是使用基於字符串的語法來描述約束：

class FilteringMixin(object): 
    FILTER_TYPES = { 
     'whitelist': 0, 
     'blacklist': 1, 
    } 

    @declared_attr 
    def filter_type(cls): 
     return db.Column(db.SmallInteger, nullable=False, 
         default=cls.FILTER_TYPES['whitelist']) 

    @declared_attr 
    def __table_args__(cls): 
     return (
      db.CheckConstraint(
       'filter_type in (%s)' % 
       ','.join(str(t) for t in cls.FILTER_TYPES.values())), 
     ) 


class FilteredConnectionType(FilteringMixin, db.Model): 
    CONNECTION_TYPES = { 
     'wifi': 0, 
     'cellular': 1, 
    } 

    __tablename__ = 'filtered_connection_types' 
    # Changed to db.Integer from db.BigInteger because of SQLite 
    id = db.Column(db.Integer, primary_key=True) 
    connection_type = db.Column(db.SmallInteger, nullable=False, 
           default=CONNECTION_TYPES['cellular']) 

    @declared_attr 
    def __table_args__(cls): 
     return (
      db.CheckConstraint(cls.connection_type.in_(cls.CONNECTION_TYPES.values())), 
     ) + FilteringMixin.__table_args__ 

測試代碼：

# saves the record with defaults 
conn_type = FilteredConnectionType() 
session.add(conn_type) 
session.commit() 

# raises an error: Check constraint failed 
conn_type = FilteredConnectionType(filter_type=3) 
session.add(conn_type) 
session.commit() 

注：

• FilteringMixin擴展的對象，而不是db.Model
• 我不是100％肯定，但你可能並不需要@declared_attr.cascading，但只是@declared_attr
• 在FilteringMixin我重命名使用基於字符串的語法來定義約束。
• 完整的例子就是here
• SQLAlchemy的文檔參考 - declared_arrt和Mixin and Custom Base Classes