python - flask-sqlalchemy multiple relationship types between two tables -

i having trouble setting multiple relationships between 2 models. these 2 models 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.relationship('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.relationship('product', backref='product_images') 

product should have one-to-one cover image, , 1 many gallery of other images. however, there circular dependency foreign keys.

i in 2 tables. there way implement these 2 relationships?

at point code above throws:

sqlalchemy.exc.ambiguousforeignkeyserror 

there 2 circular dependencies here:

1. the foreign keys mutually dependent on existence of each table. 1 of fks must created after dependent table exists. set use_alter=true , name='some_name on 1 resolve this.
2. the relationships both need resolve primary_key of target after insert, mutually dependent on both having been commited. set post_update=true on 1 resolve this.

see following documentation:

• circulardependencyerror
• dependent foreign keys
• dependent relationships

here working example demonstrating solution.

from sqlalchemy import create_engine, column, integer, string, foreignkey, table sqlalchemy.ext.declarative import declarative_base sqlalchemy.orm import sessionmaker, relationship  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 name='' adds foreign key after image has been created avoid circular dependency     cover_id = column(integer, foreignkey('image.id', use_alter=true, name='fk_product_cover_id'))      # cover image one-to-one relationship     # set post_update=true avoid circular dependency during     cover = relationship('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 = relationship(product, foreign_keys=product_id, backref='images')      # nothing special need in image, circular dependencies solved in product   base.metadata.create_all()  # create images i1 = image(path='img1') i2 = image(path='img2') i3 = image(path='img3') i4 = image(path='img4')  # create product images, 1 of cover p1 = product(name='sample', images=[i1, i2, i3, i4], cover=i2)  session.add(p1) session.commit()  print 'cover:', p1.cover.path  # prints 1 cover image path print 'images:', [i.path in p1.images]  # prints 4 gallery image paths  print 'image product:', p1.images[0].product.name  # prints product name image perspective