flask

flask-sqlalchemy两个表之间的多种关系类型(flask-sqlalchemy multiple relatihip types between two tables)

我在两个模型之间建立多个关系时遇到问题。 这些是我现在拥有的两个型号：

class Product(db.Model): tablename='product' id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String(50)) image_id = db.Column(db.Integer, db.ForeignKey('image.id')) image = db.relatihip('Image',uselist=False,backref=db.backref('product')) class Image(db.Model): __tablename__='address' id = db.Column(db.Integer, primary_key=True) normal = db.Column(db.String(200)) product_id = db.Column(db.Integer, db.ForeignKey('product.id')) product = db.relatihip('Product', backref='product_images')

产品应该与封面图像一对一，以及与其他图像库一对一的产品。 但是，外键存在循环依赖关系。

我想只在两张桌子里这样做。 有没有其他方法来实现这两种关系？

此时代码抛出：

AmbiguousForeignKeysError

I am having trouble setting up multiple relatihips between two models. These are my two models as I have them now:

class Product(db.Model): tablename='product' id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String(50)) image_id = db.Column(db.Integer, db.ForeignKey('image.id')) image = db.relatihip('Image',uselist=False,backref=db.backref('product')) class Image(db.Model): __tablename__='address' id = db.Column(db.Integer, primary_key=True) normal = db.Column(db.String(200)) product_id = db.Column(db.Integer, db.ForeignKey('product.id')) product = db.relatihip('Product', backref='product_images')

Product should have a one-to-one with a cover image, and a one to many with a gallery of other images. However, there is a circular dependency with the foreign keys.

I would like to do this in only two tables. Is there another way to implement these two relatihips?

At this point code above throws:

AmbiguousForeignKeysError

最满意答案

这里有两个循环依赖：

外键相互依赖于每个表的存在。 必须在依赖表已存在之后创建其中一个fks。 在一个上设置use_alter=True和name='some_name以解决此问题。 这些关系都需要在插入后解析其目标的primary_key，但是相互依赖于已经提交的两者。 在一个上设置post_update=True以解决此问题。

请参阅以下文档：

CircularDependencyError 依赖外键 依赖关系

这是一个展示解决方案的工作示例。

from sqlalchemy import create_engine, Column, Integer, String, ForeignKey, Table from declarative import declarative_base from import sessionmaker, relatihip engine = create_engine('sqlite:///:memory:', echo=True) Session = sessionmaker(bind=engine) session = Session() Base = declarative_base(bind=engine) class Product(Base): __tablename__ = 'product' id = Column(Integer, primary_key=True) name = Column(String, nullable=False) # cover image foreign key # use_alter=True along with name='' adds this foreign key after Image has been created to avoid circular dependency cover_id = Column(Integer, ForeignKey('image.id', use_alter=True, name='fk_product_cover_id')) # cover image one-to-one relatihip # set post_update=True to avoid circular dependency during cover = relatihip('Image', foreign_keys=cover_id, post_update=True) class Image(Base): __tablename__ = 'image' id = Column(Integer, primary_key=True) path = Column(String, nullable=False) product_id = Column(Integer, ForeignKey(Product.id)) # product gallery many-to-one product = relatihip(Product, foreign_keys=product_id, backref='images') # nothing special was need in Image, all circular dependencies were solved in Product _all() # create some images i1 = Image(path='img1') i2 = Image(path='img2') i = Image(path='img') i4 = Image(path='img4') # create a product with those images, one of which will also be the cover p1 = Product(name='sample', images=[i1, i2, i, i4], cover=i2) session.add(p1) () print 'cover:', path # prints one cover image path print 'images:', [i.path for i in p1.images] # prints 4 gallery image paths print 'image product:', p1.images[0]. # prints product name from image perspective

There are two circular dependencies here:

The foreign keys are mutually dependent on the existence of each table. One of the fks must be created after the dependent table already exists. Set use_alter=True and name='some_name on one to resolve this. The relatihips both need to resolve the primary_key of their target after insert, but are mutually dependent on both having already been commited. Set post_update=True on one to resolve this.

See the following documentation:

CircularDependencyError Dependent foreign keys Dependent relatihips

Here is a working example demtrating the solution.

from sqlalchemy import create_engine, Column, Integer, String, ForeignKey, Table from declarative import declarative_base from import sessionmaker, relatihip engine = create_engine('sqlite:///:memory:', echo=True) Session = sessionmaker(bind=engine) session = Session() Base = declarative_base(bind=engine) class Product(Base): __tablename__ = 'product' id = Column(Integer, primary_key=True) name = Column(String, nullable=False) # cover image foreign key # use_alter=True along with name='' adds this foreign key after Image has been created to avoid circular dependency cover_id = Column(Integer, ForeignKey('image.id', use_alter=True, name='fk_product_cover_id')) # cover image one-to-one relatihip # set post_update=True to avoid circular dependency during cover = relatihip('Image', foreign_keys=cover_id, post_update=True) class Image(Base): __tablename__ = 'image' id = Column(Integer, primary_key=True) path = Column(String, nullable=False) product_id = Column(Integer, ForeignKey(Product.id)) # product gallery many-to-one product = relatihip(Product, foreign_keys=product_id, backref='images') # nothing special was need in Image, all circular dependencies were solved in Product _all() # create some images i1 = Image(path='img1') i2 = Image(path='img2') i = Image(path='img') i4 = Image(path='img4') # create a product with those images, one of which will also be the cover p1 = Product(name='sample', images=[i1, i2, i, i4], cover=i2) session.add(p1) () print 'cover:', path # prints one cover image path print 'images:', [i.path for i in p1.images] # prints 4 gallery image paths print 'image product:', p1.images[0]. # prints product name from image perspective