Python SqlAlchemy外键约束

当我插入新记录时，我在理解ForeignKey约束如何与SqlAlchemy一起工作时遇到了一个问题。我有一个父表，它有两个子表，每一个子表都是一对多关系。我的底层数据库是Oracle，下面是我的表的简化模型：

class ProductCategory(db.Model):
  __tablename__ = 'productcategory'
  product_category_id = Column(Integer, Sequence('productcategory_seq', primary_key=True)
  label = Column(String)
  products = relation('Product', backref='product_category')
  printers = relation('Printer', backref='product_category')

class Product(db.Model):
  __tablename__ = 'product'
  product_id = Column(Integer, Sequence('product_seq'), primary_key=True)
  product_category_id = Column(Integer, ForeignKey('productcategory.product_category_id')
  name = Column(String)

class Printer(db.Model):
  __tablename__ = 'printer'
  printer_id = Column(Integer, Sequence('printer_seq'),
  product_category_id = Column(Integer, ForeignKey('product_category.product_category_id')
  name = Column(String)

下面是一个Python代码的简化示例，它引发了一个（cx_Oracle.integrityyror）ORA-02291:integrity约束（EASTLAB.SYS_C0049050）冲突-父键未找到异常

try:
  product_category = ProductCategory(label='some_category')
  db.session.add(product_category)

  # iterate over the products in the category
  for product in products:
    new_product = Product(
      product_category=product_category,
      name=product.name
    )
    db.session.add(new_product)

  # iterate over the printers in the category
  for printer in printers:
    new_printer = Printer(
      product_category=product_category,
      name=printer.name
    )
    db.session.add(new_printer)

  # commit before exiting context manager
  db.session.commit()
except:
  db.session.rollback()

在执行db.session.commit（）代码时引发异常。我不知道为什么会提出这个例外，我在上面所做的似乎是我在各种在线帖子中看到的一种模式。有趣的是，如果我注释掉添加打印机子项的代码，这就可以了。我很困惑……：）

任何帮助、指点或建议都将不胜感激

提前感谢,，

---

Doug

打印机上的外键

product\u category\u id

引用的是

'product\u category.product\u id'

，而不是

'productcategory.product\u category\u id'

使用以下适用于我的工具对此进行了测试：

class ProductCategory(Base):
    __tablename__ = 'productcategory'
    product_category_id = Column(Integer, Sequence('productcategory_seq'), primary_key=True)
    label = Column(String)
    products = relation('Product', backref='product_category')
    printers = relation('Printer', backref='product_category')


class Product(Base):
    __tablename__ = 'product'
    product_id = Column(Integer, Sequence('product_seq'), primary_key=True)
    product_category_id = Column(Integer, ForeignKey('productcategory.product_category_id'))
    name = Column(String)


class Printer(Base):
    __tablename__ = 'printer'
    printer_id = Column(Integer, Sequence('printer_seq'), primary_key=True)
    product_category_id = Column(Integer, ForeignKey('productcategory.product_category_id'))
    name = Column(String)


Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()

product_category = ProductCategory(label='some_category')
session.add(product_category)

product_names = ["a", "b", "c"]

# iterate over the products in the category
for product in product_names:
    new_product = Product(
        product_category=product_category,
        name=product
    )
    session.add(new_product)

printer_names = ["a", "b", "c"]

# iterate over the printers in the category
for printer in printer_names:
    new_printer = Printer(
        product_category=product_category,
        name=printer
    )
    session.add(new_printer)

# commit before exiting context manager
session.commit()

---

与您的示例略有不同，当您将示例添加到问题中时，您省略了一些结束括号，我稍微改变了它获取

打印机

和

产品

样本的方式，

打印机

上的外键

产品类别id

正在引用

'product\u category.product\u category\u id'

而非

'productcategory.product\u category\u id'

使用以下适用于我的工具对此进行了测试：

class ProductCategory(Base):
    __tablename__ = 'productcategory'
    product_category_id = Column(Integer, Sequence('productcategory_seq'), primary_key=True)
    label = Column(String)
    products = relation('Product', backref='product_category')
    printers = relation('Printer', backref='product_category')


class Product(Base):
    __tablename__ = 'product'
    product_id = Column(Integer, Sequence('product_seq'), primary_key=True)
    product_category_id = Column(Integer, ForeignKey('productcategory.product_category_id'))
    name = Column(String)


class Printer(Base):
    __tablename__ = 'printer'
    printer_id = Column(Integer, Sequence('printer_seq'), primary_key=True)
    product_category_id = Column(Integer, ForeignKey('productcategory.product_category_id'))
    name = Column(String)


Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()

product_category = ProductCategory(label='some_category')
session.add(product_category)

product_names = ["a", "b", "c"]

# iterate over the products in the category
for product in product_names:
    new_product = Product(
        product_category=product_category,
        name=product
    )
    session.add(new_product)

printer_names = ["a", "b", "c"]

# iterate over the printers in the category
for printer in printer_names:
    new_printer = Printer(
        product_category=product_category,
        name=printer
    )
    session.add(new_printer)

# commit before exiting context manager
session.commit()

与您的示例略有不同，当您将示例添加到问题中时，您省略了一些结束括号，我稍微改变了它获取

打印机

和

产品

样本的方式