如果从数据库获取模型实例，则调用save方法将始终更新该实例。例如：

  t = TemperatureData.objects.get（id = 1）
 t.value = 999＃字段
 t.save（）＃这将只更新
 

如果您的目标是防止任何INSERT，那么你可以覆盖 save 方法，测试主键是否存在并引发异常。有关详细信息，请参阅以下内容：

• Django如何知道UPDATE与INSERT

I have a model in django that I want to update only, that is, when I call it and set the data, it will not create a new record, only update the existing one. How can I do this? Here is what I have:

class TemperatureData(models.Model):   
    date = models.DateTimeField()   
    value = models.PositiveIntegerField()   
    alert = models.BooleanField()

If you get a model instance from the database, then calling the save method will always update that instance. For example:

t = TemperatureData.objects.get(id=1)
t.value = 999  # change field
t.save() # this will update only

If your goal is prevent any INSERTs, then you can override the save method, test if the primary key exists and raise an exception. See the following for more detail:

• How Django knows to UPDATE vs. INSERT