适用于MYSQL的ASCII和Unicode中的SQLAlchemy大字符串

Question

在python类中，SQLAlchemy您必须为字符串变量指定最大字符长度。例如，url = Column(String(200))我有兴趣存储一个大字符串，但是当我尝试设置时mytextfield = Column(String(2**30))，出现以下错误：

OperationalError: (OperationalError) (1074, "Column length too big for column 'textfield' (max = 21845); use BLOB or TEXT instead") '\nCREATE TABLE users (\n\tid INTEGER NOT NULL AUTO_INCREMENT, \n\tname VARCHAR(50), \n\tfullname VARCHAR(50), \n\tpassword VARCHAR(12), \n\ttextfield VARCHAR(2147483648), \n\tPRIMARY KEY (id)\n)\n\n' ()

如何保持ascii编码但增加SQLAlchemy对象Base类中字符串的最大长度？如果我要切换为使用unicode，mytextfield = Column(UnicodeText(2**30))我是否认为这将默认为utf-8，并且不会增加标准英文字符的存储大小？如果它是在utf-8中，并且我从SQL数据库中检索了一个条目，text = u'my text here'即使最初输入的内容是文本，该文本也将等效于text = 'my text here'？

这是我当前的代码：

from sqlalchemy import create_engine
engine = create_engine("mysql://user:password@host/database")

from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

from sqlalchemy import Column, Integer, String, Sequence, UnicodeText

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, Sequence('user_id_seq'), primary_key=True)
    name = Column(String(50))
    fullname = Column(String(50))
    password = Column(String(12))
    textfield = Column(String(length=2**31))

    def __init__(self, name, fullname, password, textfield):
        self.name = name
        self.fullname = fullname
        self.password = password
        self.textfield = textfield

    def __repr__(self):
        return "<User('%s','%s', '%s', '%s')>" % (self.name, self.fullname, self.password, self.textfield)


from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship, backref

class Address(Base):
     __tablename__ = 'addresses'
     id = Column(Integer, Sequence('user_id_seq'), primary_key=True)
     email_address = Column(String(100), nullable=False)
     user_id = Column(Integer, ForeignKey('users.id'))

     user = relationship("User", backref=backref('addresses', order_by=id))

     def __init__(self, email_address):
         self.email_address = email_address

     def __repr__(self):
         return "<Address('%s')>" % self.email_address



Base.metadata.create_all(engine)

mytext = "Peter Piper picked a peck of pickled peppers. A peck of pickled peppers Peter Piper picked. If Peter Piper picked a peck of pickled peppers, Where's the peck of pickled peppers that Peter Piper picked?"
new_user = User('Pete', 'Peter Piper', 'peppy', mytext)


from sqlalchemy.orm import sessionmaker
Session = sessionmaker()
Session.configure(bind=engine)

session = Session()
session.add(new_user)
session.commit()

Answer 1

使用Text或UnicodeText代替String或Unicode。

文本映射到CLOB（TEXT）字段，可以存储大量数据字符串映射到VARCHAR字段，通常限制为2 ^ 31-1