SQLalchemy AttributeError:'str'对象没有属性'_sa_instance_state'

Question

我正在尝试使用SQLAlchemy + Python向我的数据库添加一个项目,但不断收到错误.

我的database_setup.py:

class company(Base):
    __tablename__ = 'company'
    compID = Column(Integer, primary_key = True)
    name = Column(String(80), nullable = False)

class item(Base):
    __tablename__ = 'items'
    itemID = Column(Integer, primary_key = True)
    name = Column(String(80), nullable = False)
    category = Column(String(250))
    description = Column(String(250))
    price = Column(String(8))
    compID = Column(Integer, ForeignKey('company.compID'))
    company = relationship(company)

将sqlalchemy导入终端后,我定义了一个要插入的项目:

JawboneUP3 = item(
    itemID="1",
    name="Jawbone UP3",
    description="The latest UP!", 
    category="tracker",
    price="$174.99",
    company="Jawbone"
)

并绘制一个会话来添加和提交:

session.add(JawboneUP3)
session.commit()

当我提交时,我不断收到此错误:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1399, in add
    self._save_or_update_state(state)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1417, in _save_or_update_state
    halt_on=self._contains_state):
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 2037, in cascade_iterator
    parent_dict, visited_states, halt_on))
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/properties.py", line 932, in cascade_iterator
    get_all_pending(state, dict_)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/attributes.py", line 761, in get_all_pending
   ret = [(instance_state(current), current)]
AttributeError: 'str' object has no attribute '_sa_instance_state'

我在公司表中添加了一个"Jawbone"对象,我理解我的'JawboneUP3'应该与之相关.通过我通过我的webserver脚本启用的浏览器表单正确添加了此对象.我相信我应该可以直接从终端添加项目.

Answer 1

我认为问题在于您如何定义相关的公司架构:

JawboneUP3 = item(itemID = "1", name = "Jawbone UP3", description = "The latest UP!", 
                  category = "tracker", price = "$174.99", company = "Jawbone")
                                                           # HERE^

该item构造函数需要一个company实例,但你传递一个字符串值.修理它:

JawboneUP3 = item(itemID="1", 
                  name="Jawbone UP3", 
                  description="The latest UP!", 
                  category="tracker", 
                  price="$174.99", 
                  company=company(name="Jawbone"))

Answer 2

首先，在 Python 中定义类时，最好以大写字母开头，如下所示：

class Company(Base):
    __tablename__ = 'company'
    compID = Column(Integer, primary_key = True)
    name = Column(String(80), nullable = False)

class Item(Base):
    __tablename__ = 'items'
    itemID = Column(Integer, primary_key = True)
    name = Column(String(80), nullable = False)
    category = Column(String(250))
    description = Column(String(250))
    price = Column(String(8))
    compID = Column(Integer, ForeignKey('company.compID'))
    company = relationship(company)

话虽如此，这不是您的代码抛出错误的原因。:)

原因

该Item构造期望对象的一个实例Company被作为变量的值来传递company

解决方案 1：您的数据库中不存在Jawbone公司

这里@alecxe 的答案是有效的。

您应该将代码替换为：

JawboneUP3 = Item(itemID="1", 
                  name="Jawbone UP3", 
                  description="The latest UP!", 
                  category="tracker", 
                  price="$174.99", 
                  company=company(name="Jawbone"))

将此对象添加到会话并提交更改实际上会在您的数据库中创建两个条目：

• 项目条目，名称为“Jawbone UP3”
• 公司数据库中的一行，名为“Jawbone”的公司

解决方案 2：Jawbone公司存在于您的数据库中

在这里，您应该从表“company”中获取公司Jawbone并将其作为参数传递给Item构造函数，如下所示：

jawbone = session.query(Company).filter_by(name="Jawbone").first()

JawboneUP3 = Item(itemID="1", 
                  name="Jawbone UP3", 
                  description="The latest UP!", 
                  category="tracker", 
                  price="$174.99", 
                  company=jawbone)

对于session部分检查这个