flask-sqlarchemy 多对多关联如何定义？使用的是第三张表，不知道怎么查询，可能定义有错误

class Theme_Product(db.Model):
    __tablename__ = 'theme_product'
    theme_id=db.Column(db.Integer,db.ForeignKey('theme.id'), primary_key=True)
    product_id=db.Column(db.Integer,db.ForeignKey('product.id'), primary_key=True)

主题表简化

class Theme(db.Model):
    __tablename__ = 'theme'
    id = db.Column(db.Integer, primary_key=True)
    productInTheme=db.relationship('Theme_Product',
                                    foreign_keys=[Theme_Product.theme_id],
                                    backref=db.backref('backTheme',lazy='joined'),
                                    lazy='dynamic',
                                    cascade='all,delete-orphan')

产品表

class Product(db.Model):
    __tablename__ = 'product'
    id = db.Column(db.Integer, primary_key=True)
    theme=db.relationship('Theme_Product',
                            foreign_keys=[Theme_Product.product_id],
                            backref=db.backref('backProduct', lazy='joined'),
                            lazy='dynamic',
                            cascade='all,delete-orphan')

查询语句
- 从 theme 查询其下属包含的所有 product
- 导入 Theme 类
  Theme.query.get(id).productInTheme
  - 此时提示<class 'sqlalchemy.orm.dynamic.AppenderBaseQuery'>
- Theme.query.get(id).productInTheme
  - 无法错误提示很乱，感觉像是 id 相互对应不上什么的

-----------------------跪求指点，如何查询--------------------------------

3 replies • 2018-03-22 16:59:38 +08:00

vZexc0m

Mar 21, 2018

```
tags = db.Table('article_tag',
db.Column('article_id', db.Integer(), db.ForeignKey('article.id')),
db.Column('tag_id', db.Integer(), db.ForeignKey('tag.id')))

class Article(db.Model):
id = db.Column(db.Integer(), primary_key=True)
title = db.Column(db.String(255))
text = db.Column(db.Text())
publish_time = db.Column(db.DateTime(), default=datetime.datetime.utcnow)
comments = db.relationship("Comment", backref='article', lazy='dynamic')
tags = db.relationship('Tag',
secondary=tags,
backref=db.backref('article', lazy='dynamic'))

def json(self):
return dict(
id=self.id,
title=self.title,
text=self.text,
publish_time=utc_local(self.publish_time),
username=self.user.username,
tags=[tag.name for tag in self.tags]
)

def __str__(self):
return "<Article {}>".format(self.title)

def __repr__(self):
return "<Article {}>".format(self.title)

class Tag(db.Model):
id = db.Column(db.Integer(), primary_key=True)
name = db.Column(db.String(255))

def __str__(self):
return "<Tag {}>".format(self.name)

def __repr__(self):
return "<Tag {}>".format(self.name)
```

sevenQu

Mar 21, 2018

@vZexc0m 这样定义，第三张表的数据怎么用？这样数据只能从零开始吧

kimchan

Mar 22, 2018

@sevenQu 看 1 楼代码的 relationship 的定义. 就是用那个去使用