Question

这可能是一个相对简单的问题。但是，为了完整起见，我将包含所有代码。

我正在使用找到的类here为我的MySQL表生成字母数字主键。但是，当我将一行上传到数据库时，我收到此错误：

FlushError: Instance <User at 0x1d47110> has a NULL identity key.  If this is an auto-generated value, check that the database table allows generation of new primary key values, and that the mapped Column object is configured to expect these generated values.  Ensure also that this flush() is not occurring at an inappropriate time, such as within a load() event.

因此，当我使用来自SQLAlchemy源代码的GUID代码时，这是代码：

User.py

from app import db
from app.custom_db.GUID import GUID

class User(db.Model):
  __tablename__ = 'users'
  id = db.Column(GUID(), primary_key = True)
  name = db.Column(db.String(40), unique = True)
  email_stub = db.Column(db.String(30), unique = True)

  def __init__(self, name, email_stub):
    self.name = name
    self.email_stub = email_stub

  def __repr__(self):
    return '<User %r>' % self.name

当我使用db.Integer时，它运行正常。但是，就像我说我想要使用字母数字uuid4()主键。当我这样做时，如何让我的MySQL数据库不抱怨？

Answer 1

您需要为主键分配default generation function。在这里，我们还将使用backend-agnostic GUID type示例的简化版本，以便我们看到真正的uuids：

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
import uuid

Base = declarative_base()

class GUID(TypeDecorator):
    impl = String(32)

    def process_bind_param(self, value, dialect):
        if value is not None:
            return "%.32x" % value
        else:
            return MNone

    def process_result_value(self, value, dialect):
        if value is None:
            return value
        else:
            return uuid.UUID(value)

class User(Base):
    __tablename__ = 'users'
    id = Column(GUID(), primary_key=True, default=uuid.uuid4)
    name = Column(String(40), unique=True)

e = create_engine("mysql://scott:tiger@localhost/test", echo=True)
Base.metadata.drop_all(e)  # just for testing here
Base.metadata.create_all(e)

s = Session(e)

s.add_all([User(name='u1'), User(name='u2'), User(name='u3')])
s.commit()

for guid in s.query(User.id):
    print(guid)

配置MySQL以允许生成主键值

1 个答案: