保存带有外键引用的序列化程序时 Django 失败答案

【问题标题】：Django fails when saving a serializer with foreign key references保存带有外键引用的序列化程序时 Django 失败
【发布时间】：2019-01-15 21:09:09
【问题描述】：

所以我有一个带有一个外键引用的模型，它在几周内运行良好。我最终不得不向模型添加另一个外键引用，现在我无法使用序列化程序保存任何记录。我应该提到我正在使用 Django 2.1。这是我正在使用的模型（为简单起见，删除了一些字段）：

class Finding(models.Model):
    finding_id = models.IntegerField(null=False, blank=False, primary_key=True, db_index=True)
    name = models.CharField(null=True, blank=True, max_length=255)
    web_app = models.ForeignKey(WebApplication, on_delete=models.CASCADE)
    q_id = models.ForeignKey(StagingQkb, on_delete=models.CASCADE)

新的 FK 是 q_id 字段。这只是一个简单的 int 之前。我实际上已经炸毁了旧表，而新表仍然完全是空的，所以我知道现有数据没有问题（带有外键的表仍然完好无损）。之前保存结果时，我只会为“web_app”提供 WebApplication 对象的 PK。据我所知，这仍然有效。 'q_id' 字段，当以相同的方式插入时，抱怨它需要一个 int/string/bytes 而不是 StagingQkb 对象。好吧，我没有给它一个 StagingQkb 对象，所以给它什么！

这是序列化程序：

class FindingSerializer(serializers.ModelSerializer):

    class Meta:
        model = Finding
        fields = '__all__'

我提供给序列化程序的数据如下所示：

data = {'finding_id': 5514989,
        'name': 'Sample-Name',
        'q_id': 12345,
        'web_app': 67890}

当我将数据插入序列化程序时，我正在执行以下操作：

>>> fs = FindingSerializer(data=data)
>>> fs.is_valid()
True
>>> fs.save()

运行上述代码后出现的错误如下所示：

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/opt/oss/python35/lib/python3.5/site-packages/rest_framework/serializers.py", line 214, in save
    self.instance = self.create(validated_data)
  File "/opt/oss/python35/lib/python3.5/site-packages/rest_framework/serializers.py", line 959, in create
    raise TypeError(msg)
TypeError: Got a `TypeError` when calling `Finding.objects.create()`. This may be because you have a writable field on the serializer class that is not a valid argument to `Finding.objects.create()`. You may need to make the field read-only, or override the FindingSerializer.create() method to handle this correctly.
Original exception was:
 Traceback (most recent call last):
  File "/opt/oss/python35/lib/python3.5/site-packages/rest_framework/serializers.py", line 940, in create
    instance = ModelClass._default_manager.create(**validated_data)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/query.py", line 413, in create
    obj.save(force_insert=True, using=self.db)
  File "/home/dpz3w0q/AutonomousPrimeD/autonomousprimed/Finding/models.py", line 83, in save
    q_id=self.q_id)
  File "/home/dpz3w0q/AutonomousPrimeD/autonomousprimed/Finding/models.py", line 173, in evaluate
    if ScoreMatrix.objects.filter(q_id=q_id).count() > 0:
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/query.py", line 844, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/query.py", line 862, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1263, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1287, in _add_q
    split_subq=split_subq,
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1225, in build_filter
    condition = self.build_lookup(lookups, col, value)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1096, in build_lookup
    lookup = lookup_class(lhs, rhs)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/lookups.py", line 20, in __init__
    self.rhs = self.get_prep_lookup()
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/lookups.py", line 70, in get_prep_lookup
    return self.lhs.output_field.get_prep_value(self.rhs)
  File "/opt/oss/python35/lib/python3.5/site-packages/django/db/models/fields/__init__.py", line 1807, in get_prep_value
    return int(value)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'StagingQkb'

我完全被困在这里了。我没有改变将数据传递给序列化程序的方式，所以我真的不知道我做错了什么。如果有人能够帮助我解决这个问题，我将不胜感激！

【问题讨论】：

回溯似乎表明在models.py 中运行了一些额外的代码——可能从Finding.save() 调用。你能显示来自models.py的所有代码吗？
您好，谢谢，这是一个很好的观点！保存方法如下所示： def save(self, force_insert=False, force_update=False, using=None, update_fields=None): if self.web_app.sys_id is not None and self.web_app.sys_id.composite_dav is not None and \ self.q_type 不是 'INFORMATION_GATHERED': self.rating = ScoreMatrix.evaluate(dav=self.web_app.sys_id.composite_dav, severity=self.severity, q_id=self.q_id) else: self.rating = None super() .save()
我将尝试更改对 self.q_id 的引用以引用外部表的 PK，并在我知道它是否有效后报告。

标签： python django django-models django-rest-framework django-serializer

【解决方案1】：

感谢@WillKeeling，我意识到我在 save() 方法中引用了 Finding.q_id，但在进行 FK 更改后我忘记更新了。外表的PK是qkb_id，所以我把引用改成Finding.q_id.qkb_id就可以保存模型了。

【讨论】：