I have a function which currently calls Models.object.get()
, which returns either 0 or 1 model objects. If it returns 0, I create a new model instance in the except DoesNotExist
clause of the function. Otherwise, I would like to update the fields in the pre-existing instance, without creating a new one. I was originally attempting to call .update()
on the instance which was found, but .update()
seems to be only callable on a QuerySets. How do I get around changing a dozen fields, without calling .filter()
and comparing the lengths to know if I have to create or update a pre-existing instance?
Use update_fields in save() If you would like to explicitly mention only those columns that you want to be updated, you can do so using the update_fields parameter while calling the save() method. You can also choose to update multiple columns by passing more field names in the update_fields list.
The __lte lookup [Django-doc] means that you constrain the field that is should be less than or equal to the given value, whereas the __gte lookup [Django-doc] means that the field is greater than or equal to the given value.
str function in a django model returns a string that is exactly rendered as the display name of instances for that model.
With the advent of Django 1.7, there is now a new update_or_create
QuerySet method, which should do exactly what you want. Just be careful of potential race conditions if uniqueness is not enforced at the database level.
Example from the documentation:
obj, created = Person.objects.update_or_create( first_name='John', last_name='Lennon', defaults={'first_name': 'Bob'}, )
The
update_or_create
method tries to fetch an object from database based on the given kwargs. If a match is found, it updates the fields passed in thedefaults
dictionary.
Pre-Django 1.7:
Change the model field values as appropriate, then call .save()
to persist the changes:
try: obj = Model.objects.get(field=value) obj.field = new_value obj.save() except Model.DoesNotExist: obj = Model.objects.create(field=new_value) # do something else with obj if need be
if you want only to update model if exist (without create it):
Model.objects.filter(id = 223).update(field1 = 2)
mysql query:
UPDATE `model` SET `field1` = 2 WHERE `model`.`id` = 223
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