Question

当我插入新记录时，我在理解ForeignKey约束如何与SqlAlchemy一起工作时遇到问题。我有一个包含两个子表的父表，每个子表都是one_2_many关系。我的底层数据库是Oracle，这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)

这是一个Python代码的简化示例，该代码违反了（cx_Oracle.IntegrityError）ORA-02291：完整性约束（EASTLAB.SYS_C0049050） - 未找到父密钥异常

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。我不确定为什么要提出异常，我上面所做的似乎是我在各种在线帖子中看到的模式。有趣的是，如果我注释掉添加打印机子代的代码，这样可以正常工作。我非常困惑......：）

非常感谢任何帮助，指示或建议！

提前致谢，道格

Answer 1

product_category_id上的外键Printer引用'product_category.product_category_id'而非'productcategory.product_category_id'。

使用下面的测试对我有用：

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，因为当您将示例添加到问题中时，您遗漏了一些右括号，我略微更改了Printers和Products的示例。

SqlAlchemy外键约束

1 个答案: