sqlite3 – 在非可空列中忽略的默认值

from sqlalchemy import MetaData,Table,Boolean,Column

def upgrade(migrate_engine):
    meta = MetaData(bind=migrate_engine)
    message_table = Table('message',meta,autoload=True)
    col = Column('include_signature',Boolean(),default=True,nullable=False)
    col.create(message_table)

这导致了一个相当令人费解的错误：

File "src/adhocracy/migration/versions/061_optional_massmessage_signature.py",line 7,in upgrade
    col.create(message_table)
  File "eggs/sqlalchemy_migrate-0.7.2-py2.6.egg/migrate/changeset/schema.py",line 528,in create
    engine._run_visitor(visitorcallable,self,connection,**kwargs)
  File "eggs/SQLAlchemy-0.7.10-py2.6-linux-x86_64.egg/sqlalchemy/engine/base.py",line 2302,in _run_visitor
    conn._run_visitor(visitorcallable,element,line 1972,in _run_visitor
    **kwargs).traverse_single(element)
  File "eggs/sqlalchemy_migrate-0.7.2-py2.6.egg/migrate/changeset/ansisql.py",line 53,in traverse_single
    ret = super(AlterTableVisitor,self).traverse_single(elem)
  File "eggs/SQLAlchemy-0.7.10-py2.6-linux-x86_64.egg/sqlalchemy/sql/visitors.py",line 106,in traverse_single
    return meth(obj,**kw)
  File "eggs/sqlalchemy_migrate-0.7.2-py2.6.egg/migrate/changeset/databases/sqlite.py",line 75,in visit_column
    super(SQLiteColumnGenerator,self).visit_column(column)
  File "eggs/sqlalchemy_migrate-0.7.2-py2.6.egg/migrate/changeset/ansisql.py",line 101,in visit_column
    self.execute()
  File "eggs/sqlalchemy_migrate-0.7.2-py2.6.egg/migrate/changeset/ansisql.py",line 42,in execute
    return self.connection.execute(self.buffer.getvalue())
  File "eggs/SQLAlchemy-0.7.10-py2.6-linux-x86_64.egg/sqlalchemy/engine/base.py",line 1449,in execute
    params)
  File "eggs/SQLAlchemy-0.7.10-py2.6-linux-x86_64.egg/sqlalchemy/engine/base.py",line 1628,in _execute_text
    statement,parameters
  File "eggs/SQLAlchemy-0.7.10-py2.6-linux-x86_64.egg/sqlalchemy/engine/base.py",line 1698,in _execute_context
    context)
  File "eggs/SQLAlchemy-0.7.10-py2.6-linux-x86_64.egg/sqlalchemy/engine/base.py",line 1691,in _execute_context
    context)
  File "eggs/SQLAlchemy-0.7.10-py2.6-linux-x86_64.egg/sqlalchemy/engine/default.py",line 331,in do_execute
    cursor.execute(statement,parameters)
sqlalchemy.exc.OperationalError: (OperationalError) Cannot add a NOT NULL column
with default value NULL 'nALTER TABLE message ADD include_signature BOOLEAN NOT NULL' ()

据我所知,sqlalchemy缺少默认值,但我确实包含default = True！这有什么不对？

col = Column('include_signature',server_default="true",nullable=False)

其中default用于类实例,server_default用于数据库列定义.

（编辑：李大同）

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