当前上下文为空时如何处理sqlalchemy onupdate？

Question

我有一个文章模型，该模型将基于其标题插入，该模型如下所示：

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Text

Base = declarative_base()


class Article(Base):

    __tablename__ = 'article'

    id = Column(Integer, primary_key=True)
    title = Column(String(100), nullable=False)
    content = Column(Text)
    slug = Column(String(100), nullable=False,
                  default=lambda c: c.current_params['title'],
                  onupdate=lambda c: c.current_params['title'])

slug正在获取标题的价值。因此，每次文章slug都会与其标题匹配。但是，当我在不更改标题的情况下编辑内容时，会引发此异常

(builtins.KeyError) 'title' [SQL: 'UPDATE article SET content=?, slug=?,
updated_at=? WHERE article = ?'] [parameters: [{'article_id': 1,
'content': 'blah blah blah'}]]

我想是因为其中current_params不包含title。如果我更改了lambda那里并使用if，则将是None。那么我该如何处理并保持slug值与其标题匹配？

Answer 1

您可以使用validates（）装饰器：

from sqlalchemy.orm import validates

class Article(db.Model):
    __tablename__ = 'article'
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    content = db.Column(db.String)
    slug = db.Column(db.String(100), nullable=False)

    @validates('title')
    def update_slug(self, key, title):
        self.slug = title
        return title

或事件：

from sqlalchemy import event

class Article(db.Model):
    __tablename__ = 'article'
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    content = db.Column(db.String)
    slug = db.Column(db.String(100), nullable=False)

@event.listens_for(Article.title, 'set')
def update_slug(target, value, oldvalue, initiator):
    target.slug = value