Django从JSON更新/创建CounterParty模型报错：仅能创建无法更新

尝试从JSON字典列表中获取、更新或创建CounterParty模型对象，创建功能正常，但更新时报错：

TypeError: Tried to update field authentication.CounterParty.GUID with a model instance, <CounterParty: CounterParty object (3)>. Use a value compatible with UUIDField.

models.py 代码 #

class CounterParty(models.Model):
    GUID = models.UUIDField(default=uuid.uuid4, editable=True, unique=True)
    name = models.CharField(max_length=150)
    customer = models.BooleanField(default=False)
    contractor = models.BooleanField(default=False)

    class Meta:
        verbose_name_plural = 'Counter Party'

tasks.py 代码 #

def create_counter_party():
    response = [
        {
            "CounterpartyGUID": "e58ed763-928c-4155-bee9-fdbaaadc15f3",
            "CounterpartyName": "name1",
            "Customer": False,
            "Contractor": True
        },
        {
            "CounterpartyGUID": "123e4567-e89b-42d3-a456-556642440000",
            "CounterpartyName": "name2",
            "Customer": False,
            "Contractor": False
        },
    ]

    rep = response

    for item in rep:
        try:
            counter_party = CounterParty.objects.get(GUID=item['CounterpartyGUID'])
            updated_counter_party = CounterParty.objects.update(GUID=counter_party, name=item['CounterpartyName'],
                                                                customer=item['Customer'],
                                                                contractor=item['Contractor'])
            updated_counter_party.save()

        except CounterParty.DoesNotExist:
            counter_party = CounterParty.objects.create(GUID=item['CounterpartyGUID'], name=item['CounterpartyName'],
                                                        customer=item['Customer'], contractor=item['Contractor'])
            counter_party.save()

错误栈信息 #

[2023-01-28 15:29:31,894: ERROR/ForkPoolWorker-8] Task authentication.tasks.create_counter_party[a86333d9-e039-479e-8d35-37fa6b17dbfa] raised unexpected: TypeError('Tried to update field authentication.CounterParty.GUID with a model
 instance, <CounterParty: CounterParty object (3)>. Use a value compatible with UUIDField.')
Traceback (most recent call last):
  File "/home/zesshi/.local/lib/python3.9/site-packages/celery/app/trace.py", line 451, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/home/zesshi/.local/lib/python3.9/site-packages/celery/app/trace.py", line 734, in __protected_call__
    return self.run(*args, **kwargs)
  File "/mnt/c/Users/Shalltear/Desktop/Python/unica_django/authentication/tasks.py", line 27, in create_counter_party
    counter_party = CounterParty.objects.update(GUID=counter_party, name=item['CounterpartyName'],
  File "/home/zesshi/.local/lib/python3.9/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/zesshi/.local/lib/python3.9/site-packages/django/db/models/query.py", line 1191, in update
    rows = query.get_compiler(self.db).execute_sql(CURSOR)
  File "/home/zesshi/.local/lib/python3.9/site-packages/django/db/models/sql/compiler.py", line 1822, in execute_sql
    cursor = super().execute_sql(result_type)
  File "/home/zesshi/.local/lib/python3.9/site-packages/django/db/models/sql/compiler.py", line 1385, in execute_sql
    sql, params = self.as_sql()
  File "/home/zesshi/.local/lib/python3.9/site-packages/django/db/models/sql/compiler.py", line 1782, in as_sql
    raise TypeError(
TypeError: Tried to update field authentication.CounterParty.GUID with a model instance, <CounterParty: CounterParty object (3)>. Use a value compatible with UUIDField.

解决方案 #

错误根源：你使用CounterParty.objects.update()时，错误地将模型实例counter_party传给了GUID字段——该字段需要UUID格式的字符串/UUID对象，而非模型实例。另外，objects.update()是批量更新方法，你已经拿到了单个实例，直接修改属性再保存即可。

修改后的tasks.py代码 #

def create_counter_party():
    response = [
        {
            "CounterpartyGUID": "e58ed763-928c-4155-bee9-fdbaaadc15f3",
            "CounterpartyName": "name1",
            "Customer": False,
            "Contractor": True
        },
        {
            "CounterpartyGUID": "123e4567-e89b-42d3-a456-556642440000",
            "CounterpartyName": "name2",
            "Customer": False,
            "Contractor": False
        },
    ]

    for item in response:
        try:
            # 获取已存在的实例
            counter_party = CounterParty.objects.get(GUID=item['CounterpartyGUID'])
            # 直接修改实例属性
            counter_party.name = item['CounterpartyName']
            counter_party.customer = item['Customer']
            counter_party.contractor = item['Contractor']
            # 保存修改
            counter_party.save()
        except CounterParty.DoesNotExist:
            # 创建新实例
            CounterParty.objects.create(
                GUID=item['CounterpartyGUID'],
                name=item['CounterpartyName'],
                customer=item['Customer'],
                contractor=item['Contractor']
            )

更简洁的写法（推荐） #

用get_or_create减少重复逻辑：

def create_counter_party():
    response = [
        {
            "CounterpartyGUID": "e58ed763-928c-4155-bee9-fdbaaadc15f3",
            "CounterpartyName": "name1",
            "Customer": False,
            "Contractor": True
        },
        {
            "CounterpartyGUID": "123e4567-e89b-42d3-a456-556642440000",
            "CounterpartyName": "name2",
            "Customer": False,
            "Contractor": False
        },
    ]

    for item in response:
        # 不存在则创建，存在则返回已有实例
        counter_party, created = CounterParty.objects.get_or_create(
            GUID=item['CounterpartyGUID'],
            defaults={
                'name': item['CounterpartyName'],
                'customer': item['Customer'],
                'contractor': item['Contractor']
            }
        )
        # 非新创建的实例才更新属性
        if not created:
            counter_party.name = item['CounterpartyName']
            counter_party.customer = item['Customer']
            counter_party.contractor = item['Contractor']
            counter_party.save()

内容的提问来源于stack exchange，提问作者Zesshi