如何更新模型中的字段而不在 django 中创建新记录？

我在 django 中有一个模型，我只想更新它，也就是说，当我调用它并设置数据时，它不会创建新记录，只是更新现有的记录。我怎么能这么做？以下是我所知道的:

class TemperatureData(models.Model):
date = models.DateTimeField()
value = models.PositiveIntegerField()
alert = models.BooleanField()
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Django has some documentation about that on their website, see: Saving changes to objects. To summarize:

.. to save changes to an object that's already in the database, use save().

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最佳答案

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:

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You should do it this way ideally

t = TemperatureData.objects.get(id=1)
t.value = 999
t.save(['value'])

This allow you to specify which column should be saved and rest are left as they currently are in database. (https://code.djangoproject.com/ticket/4102)!

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In my scenario, I want to update the status of status based on his id

student_obj = StudentStatus.objects.get(student_id=101)
student_obj.status= 'Enrolled'
student_obj.save()

Or If you want the last id from Student_Info table you can use the following.

student_obj = StudentStatus.objects.get(student_id=StudentInfo.objects.last().id)
student_obj.status= 'Enrolled'
student_obj.save()
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Sometimes it may be required to execute the update atomically that is using one update request to the database without reading it first.

Also get-set attribute-save may cause problems if such updates may be done concurrently or if you need to set the new value based on the old field value.

In such cases query expressions together with update may by useful:

TemperatureData.objects.filter(id=1).update(value=F('value') + 1)

To update multiple fields:

TemperatureData.objects.filter(id=1).update(
value=F('value') + 1,
another_value=F('another_value')+1
)

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