SQLAlchemy one()：未找到结果

Question

我一直收到一个Traceback抱怨系统找不到结果。考虑到对象实际上正在经历这种情况，情况就不应该是这样了(我知道这一点，因为我有一个print命令来确认正在进行的查询)。我相信这个问题是在create_category_rating(..)的方法中发现的。

当我使用.one()时，它会抛出下面的抱怨。当我使用.all时，它返回AttributeError: 'list' object has no attribute '_sa_instance_state' (其他人有这个问题)。文档 at SQLAlchemy很好地定义了这些方法，但是由于某种原因，我的代码崩溃了。

问题:如果对象正在通过检索方法，是什么导致程序中断？在某个地方有个bug，我一直在为压扁它而挣扎。

我使用的是SQLAlchemy和python2.7：

回溯：

ERROR: notssdb.test.test.test1
----------------------------------------------------------------------
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 111, in test1
    api.create_category_rating(2, 'Decision-Making', 'baseball', 'Becoming a Leader')
  File "/Users/ack/code/venv/NotssDB/notssdb/api/convenience.py", line 41, in create_category_rating
    assessment_results = self.retrieve_assessment_results(owner, assessment)
  File "/Users/ack/code/venv/NotssDB/notssdb/api/object.py", line 324, in retrieve_assessment_results
    filter(Assessment_Results.owner == owner).one()
  File "/usr/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2478, in one
    raise orm_exc.NoResultFound("No row was found for one()")
NoResultFound: No row was found for one()
   # output from Traceback 
   Decision-Making
   baseball
   Becoming a Leader
   Becoming a Leader
   test1 <Assessment(name='Becoming a Leader', text='better decisions')>

convenience.py (创建方法)：

def create_category_rating(self, category_rating_int, category_name, username, name):
    category = self.retrieve_category(category_name)
    owner = self.retrieve_user(username) # added
    assessment = self.retrieve_assessment(name) #added
    assessment_results = self.retrieve_assessment_results(owner, assessment)
    return super(ConvenienceAPI, self).create_category_rating(category_rating_int, category, assessment_results)

object.py (检索方法)：

def retrieve_assessment_results(self, *args):
    id, assessment, owner = None, None, None
    if len(args) == 1:
        id, = args[0]
    elif len(args) == 2:
        assessment, owner = args
    else:
        raise ValueError('Value being passed is an object')
    if id is not None:
        return self.session.query(Assessment_Results).\
        filter(Assessment_Results.id == id).one()
    elif owner is not None:
        print 'test1', owner
        return self.session.query(Assessment_Results).\
        filter(Assessment_Results.owner == owner).one()
    elif assessment is not None:
        print 'test2', assessment
        return self.session.query(Assessment_Results).\
        filter(Assessment_Results.assessment == assessment).one()

Answer 1

你有以下几点：

self.retrieve_assessment_results(owner, assessment)

...but "retrieve_assessment_results“的参数如下(加上我的评论).

def retrieve_assessment_results(self, *args):
    id, assessment, owner = None, None, None
    if len(args) == 1:
        id, = args[0]
    elif len(args) == 2:
        assessment, owner = args # Note this line!
    else:
        raise ValueError('Value being passed is an object')

你通过业主，然后评估。但是，如果你检测到两个对象，你将读取评估，然后所有者。换句话说，您使用一个对象的顺序调用该方法，并假定相反的顺序进行检索。您甚至可以在调试行中看到这种情况：

print 'test1', owner

你会期望这个打印出类似test1 <User(...)>的东西，但是它却打印出来了.

test1 <Assessment(name='Becoming a Leader', text='better decisions')>

另外，考虑使用Python关键字参数来代替：

def retrieve_assessment_results(self, id=None, assessment=None, owner=None):
    ...

然后你的电话就变得不那么模糊了：

self.retrieve_assessment_results(owner=owner, assessment=assessment)

Answer 2

如果结果集为空，one()将引发异常。使用first()，如果没有结果，您将得到第一个结果或Python None。

关于all()也是如此，因为这个问题不包含相关的跟踪和代码。