Yes, it does, my bad.
On Wed, 28 Oct 2020 at 17:03, James Pulec <jpu...@gmail.com> wrote:
> Hey Adam,
>
> Thanks for the clarification. I totally get that this might be a bit too
> complex, and maybe shouldn't wind up in update_or_create(), so I can
> definitely just use my own manager method. I'm a little confused by this
> statement, though:
>
> "It doesn't actually fetch the updated model instance."
>
> Isn't the return obj the model instance to be updated? From what I can
> tell that's exactly what's happening in the source of update_or_create() as
> well. Am I missing something here?
>
> On Monday, October 26, 2020 at 12:22:57 PM UTC-7 Adam Johnson wrote:
>
>> I think the scenario you're suggesting is just a little too complex for
>> update_or_create. It doesn't actually fetch the updated model instance .
>> You can instead write out what you want without too much extra code using
>> get_or_create, ensuring there's a transaction and select_for_update() to
>> lock the object whilst you modify it:
>>
>> with transaction.atomic():
>> obj, created =
>> Model.objects.select_for_update().get_or_create(key=some_key,
>> defaults={"json_field": fresh_json})
>> if not created:
>> obj.json_field = merge_json(obj.json_field, fresh_json)
>> obj.save()
>>
>> If you look inside update_or_create you'll see it essentially does this
>> already. If you use the pattern frequently, you can always wrap it up in
>> your own method.
>>
>> On Mon, 26 Oct 2020 at 18:23, James Pulec <jpu...@gmail.com> wrote:
>>
>>> Since update_or_create supports callables in the defaults dictionary,
>>> I'm wondering if it's worth considering passing the existing instance (if
>>> one is found) to those callables when resolving them.
>>>
>>> The scenario I'm running into involves wanting to merge json data.
>>> Basically, I have a JSON field on the model that I'd like to do an
>>> update_or_create for, but in the case where there's an existing instance
>>> and I'd be performing an update, I'd like the merge the existing JSON data
>>> with the data I'm passing to my defaults.
>>>
>>> One way I can imagine solving for this case is to pass the existing
>>> model instance to callables defined in the defaults dictionary, if an
>>> existing model instance is found.
>>>
>>> This does feel a little gross, since you'll need to check if the passed
>>> value is None, so definitely open to other suggestion.s.
>>>
>>> Wanted to post this here before on Trac to see if there's interest,
>>> better solutions, or any concerns.
>>>
>>> Thanks!
>>>
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>>> .
>>>
>>
>>
>> --
>> Adam
>>
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Adam
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