当前上下文为空时如何处理 sqlalchemy onupdate? [英] how to handle sqlalchemy onupdate when current context is empty?

问题描述

我有一个基于标题的文章模型，模型是这样的:

I have a model of article which will have slug based on it's title, the model is like this:

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 正在获取标题的值.所以，每次文章 slug 都会匹配它的标题.但是，当我在不更改标题的情况下编辑内容时，这引发异常

slug is taking title's value. So, everytime article slug will match it's title. But, when I edit the content without changing it's title, this exception is raised

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

我猜是因为current_params 不包含title.如果，我改变lambda 在那里并使用 if，slug 将是 None.那我该如何处理这并保持 slug 值与其标题匹配?

I guess that because current_params doesn't contain title. If, I change the lambda there and using if, slug will be None. So how can I handle this and keep the slug value match it's title?

推荐答案

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

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