Hi ,
  I got the following error when do downgrade operation.

[root@localhost PushServer]# alembic downgrade base
INFO  [alembic.migration] Context impl MySQLImpl.
INFO  [alembic.migration] Will assume non-transactional DDL.
INFO  [alembic.migration] Running downgrade 3cb78fe040f4 -> 4bfc6a00969f, 
delete name2
Traceback (most recent call last):
  File "/usr/bin/alembic", line 9, in <module>
    load_entry_point('alembic==0.6.2', 'console_scripts', 'alembic')()
  File "/usr/lib/python2.6/site-packages/alembic/config.py", line 298, in 
main
    CommandLine(prog=prog).main(argv=argv)
  File "/usr/lib/python2.6/site-packages/alembic/config.py", line 293, in 
main
    self.run_cmd(cfg, options)
  File "/usr/lib/python2.6/site-packages/alembic/config.py", line 279, in 
run_cmd
    **dict((k, getattr(options, k)) for k in kwarg)
  File "/usr/lib/python2.6/site-packages/alembic/command.py", line 150, in 
downgrade
    script.run_env()
  File "/usr/lib/python2.6/site-packages/alembic/script.py", line 199, in 
run_env
    util.load_python_file(self.dir, 'env.py')
  File "/usr/lib/python2.6/site-packages/alembic/util.py", line 199, in 
load_python_file
    module = load_module(module_id, path)
  File "/usr/lib/python2.6/site-packages/alembic/compat.py", line 55, in 
load_module
    mod = imp.load_source(module_id, path, fp)
  File "alembic/env.py", line 77, in <module>
    run_migrations_online()
  File "alembic/env.py", line 70, in run_migrations_online
    context.run_migrations()
  File "<string>", line 7, in run_migrations
  File "/usr/lib/python2.6/site-packages/alembic/environment.py", line 652, 
in run_migrations
    self.get_context().run_migrations(**kw)
  File "/usr/lib/python2.6/site-packages/alembic/migration.py", line 225, 
in run_migrations
    change(**kw)
  File "alembic/versions/3cb78fe040f4_delete_name2.py", line 29, in 
downgrade
    op.drop_constraint(None, 'device')
  File "<string>", line 7, in drop_constraint
  File "<string>", line 1, in <lambda>
  File "/usr/lib/python2.6/site-packages/alembic/util.py", line 294, in go
    return fn(*arg, **kw)
  File "/usr/lib/python2.6/site-packages/alembic/operations.py", line 775, 
in drop_constraint
    self.impl.drop_constraint(const)
  File "/usr/lib/python2.6/site-packages/alembic/ddl/impl.py", line 138, in 
drop_constraint
    self._exec(schema.DropConstraint(const))
  File "/usr/lib/python2.6/site-packages/alembic/ddl/impl.py", line 76, in 
_exec
    conn.execute(construct, *multiparams, **params)
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/engine/base.py",
 
line 662, in execute
    params)
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/engine/base.py",
 
line 714, in _execute_ddl
    compiled = ddl.compile(dialect=dialect)
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/sql/expression.py",
 
line 1920, in compile
    return self._compiler(dialect, bind=bind, **kw)
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/schema.py",
 
line 2954, in _compiler
    return dialect.ddl_compiler(dialect, self, **kw)
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/engine/interfaces.py",
 
line 787, in __init__
    self.string = self.process(self.statement, **compile_kwargs)
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/engine/interfaces.py",
 
line 806, in process
    return obj._compiler_dispatch(self, **kwargs)
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/ext/compiler.py",
 
line 410, in <lambda>
    lambda *arg, **kw: existing(*arg, **kw))
  File 
"/usr/lib/python2.6/site-packages/SQLAlchemy-0.8.3-py2.6-linux-x86_64.egg/sqlalchemy/ext/compiler.py",
 
line 448, in __call__
    return fn(element, compiler, **kw)
  File "/usr/lib/python2.6/site-packages/alembic/ddl/mysql.py", line 138, 
in _mysql_drop_constraint
    "No generic 'DROP CONSTRAINT' in MySQL - "
NotImplementedError: No generic 'DROP CONSTRAINT' in MySQL - please specify 
constraint type

Something related to database settings? how to fix this guy?

Thanks.
Wesley

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