python - 具有ManyToMany的Django QuerySet传递给自定义序列化程序

我到处找，但找不到好的例子。
我有两个模特，其中一个有一个男模特。我正在尝试将需要信息的QuerySet通过ManyToManyField传递到自定义序列化程序中，并返回JSON响应。
模型.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)

视图.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，因为我有其他依赖于它的方法。当我运行此代码时，我得到：
TypeError:不可更改的类型：“list”
任何关于我如何解决这个问题的见解都是非常感谢的！以防万一，这是回溯。

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'

最佳答案

由于company是m2m字段，下面语句中的obj['company']似乎是一个列表：

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

而且，您试图通过传递一个列表作为键从company_mapdict获取一些值，这会导致此错误。
您可以使用列表理解从ID中获取公司名称：

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

您也可以按照this post进行详细解释，如果您愿意，可以在shell中亲自尝试：

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'

关于python - 具有ManyToMany的Django QuerySet传递给自定义序列化程序，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/35855584/