Question

我已经搜遍过，但找不到好的例子。

我有两个模型，其中一个有ManyToManyField。我试图通过ManyToManyField将需要信息的QuerySet传递到自定义序列化程序并返回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)

我无法更改序列化程序，因为我有其他依赖它的方法。当我运行此代码时，我得到：

TypeError：不可用类型：＆＃39; list＆＃39;

非常感谢任何有关如何解决此问题的见解！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是一个m2m字段，因此以下语句中的obj['company']似乎是一个列表：

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

并且，您试图通过将列表作为键导致company_map dict来获取某些值，这会导致此错误。

您可以使用list comprehension从ID中获取公司名称：

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

您也可以关注this post获取详细说明，如果您愿意，可以在shell中自行尝试：

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，我可能问了一个不好的问题。原来我想要做的是实际使用ForeignKey，而不是ManyToManyField。无论如何，谢谢你的帮助！

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

2 个答案: