将Django QuerySet与ManyToMany传递给自定义序列化程序

Question

我已经遍寻搜索，但找不到一个好例子。

我有两个模型，其中之一有一个ManyToManyField。我试图通过ManyToManyField将需要信息的QuerySet传递到自定义序列化器并返回JSON响应。

model.py

class Company(models.Model): 
    """Company in database.""" 

    founded = models.DateField(null=True) 
    name = models.CharField(max_length=60) 
    series = models.CharField(max_length=10, null=True) 
    valuation = models.DecimalField(max_digits=20, decimal_places=5, null=True) 
    description = models.TextField(null=True) 

    def __unicode__(self): 
     """Return human-readable representation of company for debugging.""" 

     return '<{}>'.format(self.name) 


class Metric(models.Model): 
    """Metrics for companies.""" 

    name = models.CharField(max_length=30) 
    end_date = models.DateField() 
    start_date = models.DateField() 
    company = models.ManyToManyField(Company) 
    value = models.IntegerField() 

    def __unicode__(self): 
     """Return human-readable representation of metric for debugging.""" 

     return '<{}, {}>'.format(self.name, self.company) 

views.py

class ClientAPI: 

@classmethod 
def _serialize(cls, objects): 
    def create_company_map(): 
     return {c.id: c.name for c in Company.objects.all()} 

    # Replace company ids with company names 
    def map_company(obj, company_map): 
     if 'company' in obj: 
      obj['company'] = company_map[obj['company']] 
     return obj 

    company_map = create_company_map() 
    raw = serializers.serialize('python', objects) 
    res = [dict(map_company(obj['fields'], company_map)) for obj in raw] 
    return res 

@classmethod 
def get_metrics(cls, request): 
    all_metrics = Metric.objects.all().order_by('end_date') 
    serialized_metrics = ClientAPI._serialize(all_metrics) 

    return JsonResponse(serialized_metrics, safe=False, json_dumps_params=None) 

@classmethod 
def get_metrics_by_company(cls, request, company_name): 
    metrics_by_company = Metric.objects.filter(company__name=company_name).order_by('end_date') 
    serialized_metrics_by_company = ClientAPI._serialize(metrics_by_company) 

    return JsonResponse(serialized_metrics_by_company, safe=False, json_dumps_params=None) 

我不能改变串行，因为我有一个依赖于它的其他方法。当我运行这个代码时，我得到：

TypeError: unhashable type: 'list'

任何深入了解我如何解决这一问题，都非常感谢！以防万一，这是追溯。

Traceback (most recent call last): 
    File "/Users/jackiehuynh/anaconda/lib/python2.7/site-packages/django/core/handlers/base.py", line 149, in get_response 
    response = self.process_exception_by_middleware(e, request) 
    File "/Users/jackiehuynh/anaconda/lib/python2.7/site-packages/django/core/handlers/base.py", line 147, in get_response 
    response = wrapped_callback(request, *callback_args, **callback_kwargs) 
    File "/Users/jackiehuynh/Lytmus/question_1/client/views.py", line 167, in get_metrics 
    serialized_metrics = ClientAPI._serialize(all_metrics) 
    File "/Users/jackiehuynh/Lytmus/question_1/client/views.py", line 65, in _serialize 
    res = [dict(map_company(obj['fields'], company_map)) for obj in raw] 
    File "/Users/jackiehuynh/Lytmus/question_1/client/views.py", line 60, in map_company 
    obj['company'] = company_map[obj['company']] 
TypeError: unhashable type: 'list' 

Answer 1

由于company是M2M领域，似乎obj['company']在下面的语句将是一个列表：

obj['company'] = company_map[obj['company']] 

而且，你正试图通过传递一个清单为重点，从company_map字典得到一些价值这导致了这个错误。

您可以使用列表中理解从IDS得到公司名称：

obj['company'] = [company_map.get(idx, None) for idx in obj['company']] 

您也可以按照this post的详细解释，如果你愿意，你可以试试这个自己在外壳：

In [1]: x = {'a': 1} 

In [2]: x[[1, 2]] 
--------------------------------------------------------------------------- 
TypeError         Traceback (most recent call last) 
<ipython-input-7-1032576b46f9> in <module>() 
----> 1 x[[1, 2]] 

TypeError: unhashable type: 'list' 

Answer 2

没关系，我可能会问一个不好的问题。结果我想要做的是实际使用一个ForeignKey，而不是ManyToManyField。无论如何感谢您的帮助！