InvalidRequestError: VARCHAR requires a length on dialect mysql

Question

I am trying to create a remote database using mysql on an Ubuntu machine running 12.04.

It has a root user with remote login enabled and no password.I have started the server.

output of

sudo netstat -tap | grep mysql 

shows

tcp        0      0 localhost:mysql         *:*                     LISTEN      13246/mysqld 

I have created a database called nwtopology using (as mentioned root doesn't have a password yet.)

 create database nwtopology  grant all privileges on *.* to [email protected]  FLUSH PRIVILEGES; 

From the client machine that also runs Ubuntu 12.04 I use a python script to connect to the remote mysql database using sqlalchemy.

from pox.core import core import pox.openflow.libopenflow_01 as of import re import datetime import time from sqlalchemy import create_engine, ForeignKey from sqlalchemy import Column, Date, Integer, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import relationship, backref from sqlalchemy import create_engine from sqlalchemy.orm import sessionmaker from sqlalchemy.sql.expression import exists  log = core.getLogger() engine = create_engine('mysql://[email protected]/nwtopology', echo=False) Base = declarative_base() Session = sessionmaker(bind=engine) session = Session()  class SourcetoPort(Base):     """"""     __tablename__ = 'source_to_port'     id = Column(Integer, primary_key=True)     port_no        = Column(Integer)     src_address    = Column(String,index=True)      #-----------------------------------------     def __init__(self, src_address,port_no):         """"""         self.src_address = src_address         self.port_no     = port_no   #create tables Base.metadata.create_all(engine) 

The last line

Base.metadata.create_all(engine) 

returns the error

 File "/usr/lib/python2.7/dist-packages/sqlalchemy/sql/compiler.py", line 1699, in visit_string     return self.visit_VARCHAR(type_)   File "/usr/lib/python2.7/dist-packages/sqlalchemy/dialects/mysql/base.py", line 1654, in visit_VARCHAR     self.dialect.name) InvalidRequestError: VARCHAR requires a length on dialect mysql 

What does this mean? how can I set VARCHAR length on mysql? I am very new to sqlalchemy and mysql.

Answer 1

Add the length to your String column:

src_address = Column(String(16), index=True)