继承问题：AttributeError：“str”对象没有属性“_sa_instance_state”

Question

问题：继承类没有检查字符串，因为它是作为None 传递的。

retrieve 方法的父类 (object.py) 旨在从数据库中检索对象（例如 id 或用户/评估组合）。子类 (convenience.py) 旨在接受这些对象的 strs。

object.py

def retrieve_assessment_result(self, *args):
    id, owner, assessment = None, None, None
    if len(args) == 1:
        id, = args # or id = args[0]
    elif len(args) == 2:
        owner, assessment = args
        print 'testa', owner, assessment, id
    else:
        raise ValueError('Value being passed is an object')
    if id is not None:
        print 'testi', id
        return self.session.query(Assessment_Result).\
        filter(Assessment_Result.id == id).one()
    elif owner is not None:
        print 'testo', owner
        return self.session.query(Assessment_Result).\
        filter(Assessment_Result.owner == owner).one()
    elif assessment is not None:
        print 'testa', assessment
        return self.session.query(Assessment_Result).\
        filter(Assessment_Result.assessment == assessment).one()

convenience.py

def retrieve_assessment_result(self, *args):
    id, owner, assessment = None, None, None
    if len(args) == 1:
        id, = args # or id = args[0]
        print " args = ", args
    elif len(args) == 2:
        username, name = args
        print "api args = ", args
        print 'type args', type(args)
        print 'owner: ', owner
        print 'assessment: ', assessment
    if owner is not None:
        owner = self.retrieve_user(username)
    if assessment is not None:
        assessment = self.retrieve_assessment(name)
    return super(ConvenienceAPI, self).retrieve_assessment_result(*args)

test.py

api.retrieve_assessment_result('baseball', 'Becoming a Leader')

回溯错误：

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/Users/ack/code/venv/NotssDB/notssdb/test/test.py", line 133, in test1
    api.retrieve_assessment_result('baseball', 'Becoming a Leader')
  File "/Users/ack/code/venv/NotssDB/notssdb/api/convenience.py", line 42, in retrieve_assessment_result
    return super(ConvenienceAPI, self).retrieve_assessment_result(*args)
  File "/Users/ack/code/venv/NotssDB/notssdb/api/object.py", line 327, in retrieve_assessment_result
    filter(Assessment_Result.owner == owner).one()
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/sql/operators.py", line 301, in __eq__
    return self.operate(eq, other)
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 175, in operate
    return op(self.comparator, *other, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1011, in __eq__
    other, adapt_source=self.adapter))
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1338, in _optimized_compare
    state = attributes.instance_state(state)
AttributeError: 'str' object has no attribute '_sa_instance_state'
------output--------
<Assessment_Result(owner='<User(username ='bambam', firstname ='Sean', lastname ='Cargo', email='car@gmail.com')>', assessment='<Assessment(name='Foo', text='this is foo')>')>
api args =  ('baseball', 'Becoming a Leader')
type args <type 'tuple'>
owner:  None
assessment:  None
testa baseball Becoming a Leader None
testo baseball

-----评论/建议后更新：
object.py 更新：

def retrieve_assessment_result(self, id=None, owner=None, assessment=None):
    print 'test_all_objects', owner, assessment, id
    if id is not None:
        print 'test_id_object', id
        return self.session.query(Assessment_Result).\
        filter(Assessment_Result.id == id).one()
    elif owner is not None:
        print 'test_owner_object', owner
        return self.session.query(Assessment_Result).\
        filter(Assessment_Result.owner.has(User.username == username)).one()
    elif assessment is not None:
        print 'test_assessment_object', assessment
        return self.session.query(Assessment_Result).\
        filter(Assessment_Result.assessment.has(Assessment.name == name)).one()

Convenience.py（继承自object.py）更改：

def retrieve_assessment_result(self, id=None, owner=username, assessment=name):
    if owner is not None:
        owner = self.retrieve_user(username)
    if assessment is not None:
        assessment = self.retrieve_assessment(name)
    return super(ConvenienceAPI, self).retrieve_assessment_result(id=None, owner=owner, assessment=assessment)

追溯：

  File ".../api/convenience.py", line 6, in <module>
    class ConvenienceAPI(BaseAPI):
  File "../api/convenience.py", line 37, in ConvenienceAPI
    def retrieve_assessment_result(self, id=None, owner=username, assessment=name):
NameError: name 'username' is not defined

Answer 1

根据我的经验，错误 '???' object has no attribute '_sa_instance_state 几乎总是表明您将不是 SQLAlchemy 对象的东西（即一些基本类型，如 int、str 等）分配给 @987654323 @ 或dynamic_loader。

relationship例子

>>> result = db.query(Assessment_Result).first()
>>> # owner only accepts Owner objects
>>> result.owner = "Mr. Harvey Example"
Traceback (most recent call last):
...
AttributeError: 'str' object has no attribute '_sa_instance_state'

此外，在relationship 上使用其他类型进行过滤也会导致此错误：

过滤示例

>>> Assessment_Result.owner == "baseball"
Traceback (most recent call last):
...
AttributeError: 'str' object has no attribute '_sa_instance_state'

在您的情况下，错误是由于将字符串 "baseball" 作为您传递给 Object.retrieve_assessment_result 的 2 元组 args 中的第一个条目，然后将其放入变量 owner在第二个 if 块中。

>>>         owner, assessment = args

由于owner 现在包含str，当您使用它进行过滤时，这将失败。

我想借此机会指出，这段代码的可读性不是很好，可以通过使用 keyword arguments 来改进，并且通常会使其更简洁。