AttributeError: 'int' object has no attribute '_compiler_dispatch' - flask

Question

I am using the flask-sqlalchemy extension with alembic for migrations. When I try to add a new migration file and upgrade the schema to the latest one, I get the following error:
AttributeError: 'int' object has no attribute '_compiler_dispatch'
The content of the migration file:
revision = 'ec2c2d40eb1'
down_revision = '28dda873b826'
from alembic import op
import sqlalchemy as sa
def upgrade():
op.alter_column(
'users',
'wiki_permission',
new_column_name='wiki_group',
nullable=False,
existing_nullable=False,
type_=sa.Integer(),
existing_type=sa.Integer(),
server_default=1,
existing_server_default=1 # Line of error - 27
)
def downgrade():
op.alter_column(
'users',
'wiki_group',
new_column_name='wiki_permission',
nullable=False,
existing_nullable=False,
type_=sa.Integer(),
existing_type=sa.Integer(),
server_default=1,
existing_server_default=1
)
Thanks for taking time to help me.
Edit:
The complete error message :
INFO [alembic.migration] Context impl MySQLImpl.
INFO [alembic.migration] Will assume non-transactional DDL.
INFO [alembic.migration] Running upgrade 28dda873b826 -> ec2c2d40eb1, users change column wiki_permission to wiki_group
Traceback (most recent call last):
File "/home/kevin/Code/python/flask/terminus/venv/bin/alembic", line 9, in <module>
load_entry_point('alembic==0.6.5', 'console_scripts', 'alembic')()
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/config.py", line 298, in main
CommandLine(prog=prog).main(argv=argv)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/config.py", line 293, in main
self.run_cmd(cfg, options)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/config.py", line 279, in run_cmd
**dict((k, getattr(options, k)) for k in kwarg)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/command.py", line 125, in upgrade
script.run_env()
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/script.py", line 203, in run_env
util.load_python_file(self.dir, 'env.py')
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/util.py", line 212, in load_python_file
module = load_module_py(module_id, path)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/compat.py", line 58, in load_module_py
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 "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/environment.py", line 688, in run_migrations
self.get_context().run_migrations(**kw)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/migration.py", line 258, in run_migrations
change(**kw)
File "alembic/versions/ec2c2d40eb1_users_change_column_wiki_permission_to_.py", line 27, in upgrade
existing_server_default=1,
File "<string>", line 7, in alter_column
File "<string>", line 1, in <lambda>
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/util.py", line 329, in go
return fn(*arg, **kw)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/operations.py", line 317, in alter_column
existing_autoincrement=existing_autoincrement
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/ddl/mysql.py", line 44, in alter_column
else existing_autoincrement
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/ddl/impl.py", line 76, in _exec
conn.execute(construct, *multiparams, **params)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 720, in execute
return meth(self, multiparams, params)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/sql/ddl.py", line 67, in _execute_on_connection
return connection._execute_ddl(self, multiparams, params)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 768, in _execute_ddl
compiled = ddl.compile(dialect=dialect)
File "<string>", line 1, in <lambda>
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/sql/elements.py", line 468, in compile
return self._compiler(dialect, bind=bind, **kw)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/sql/ddl.py", line 25, in _compiler
return dialect.ddl_compiler(dialect, self, **kw)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/sql/compiler.py", line 197, in __init__
self.string = self.process(self.statement, **compile_kwargs)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/sql/compiler.py", line 220, in process
return obj._compiler_dispatch(self, **kwargs)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/ext/compiler.py", line 410, in <lambda>
lambda *arg, **kw: existing(*arg, **kw))
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/ext/compiler.py", line 448, in __call__
return fn(element, compiler, **kw)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/ddl/mysql.py", line 171, in _mysql_change_column
autoincrement=element.autoincrement
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/ddl/mysql.py", line 190, in _mysql_colspec
spec += " DEFAULT %s" % _render_value(compiler, server_default)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/alembic/ddl/mysql.py", line 179, in _render_value
return compiler.sql_compiler.process(expr)
File "/home/kevin/Code/python/flask/terminus/venv/local/lib/python2.7/site-packages/sqlalchemy/sql/compiler.py", line 220, in process
return obj._compiler_dispatch(self, **kwargs)
AttributeError: 'int' object has no attribute '_compiler_dispatch'

Answer 1

Alright, I just went through this same issue. I'm not using flask-sqlalchemy, just straight alembic, but it should be identical.
Second, it worked for me with sa.Integer with no parentheses, so I would recommend that.
The alembic docs say:
When producing MySQL-compatible migration files, it is recommended that the existing_type, existing_server_default, and existing_nullable parameters be present, if not being altered.
Since it seems you are not altering these columns, the docs suggest they should be present. So:
Remove nullable, type_, and server_default. They are not being altered.
Keep existing_nullable, existing_type, and existing_server_default.