I posted on the ticket before reading this thread. Whoops. As mentioned
above it's impossible to always convert user input into the output provided
by the database without doing a round trip, because there are driver data
adapters, and django converters that both get a chance at modifying the
data as it flows through the system. We need to do a better job of
highlighting this limitation in some way.
On Tuesday, 14 February 2017 20:40:00 UTC+11, Marc Tamlyn wrote:
>
> Agreed - ensuring that this works in the general case is not reliable.
>
> On 13 February 2017 at 15:51, Adam Johnson <m...@adamj.eu <javascript:>>
> wrote:
>
>> What do you think? Absent a better suggestion, we could document this
>>> pitfall so that there's something to point to when related tickets come in.
>>
>>
>> +1, as Aymeric points out the more complex fields probably won't work
>> with coercion-on-set.
>>
>> On 13 February 2017 at 15:27, charettes <chare...@gmail.com <javascript:>
>> > wrote:
>>
>>> > What do you think? Absent a better suggestion, we could document this
>>> pitfall so that there's something to point to when related tickets come in.
>>>
>>> I also think this is the most appropriate solution.
>>>
>>> Le lundi 13 février 2017 09:57:49 UTC-5, Tim Graham a écrit :
>>>>
>>>> Once in a while, there's a ticket about this behavior:
>>>>
>>>> m = Model(decimal='12.9')
>>>> m.save()
>>>> self.assertEqual(m.decimal, '12.9')
>>>> m.refresh_from_db()
>>>> self.assertEqual(m.decimal, Decimal('12.9'))
>>>>
>>>> That is, you can create a model with an incorrect type and it won't be
>>>> fixed until you refresh the object from the database.
>>>>
>>>> Most recent complaint, "it is only a basic expectation that the DB
>>>> layer and the Application layer will correspond to each-other after
>>>> performing save, which is in other words, syncing your state with the
>>>> DB. Personally, this bug (one way binding between application and db on
>>>> save) broke many of my tests and took a lot of my time." [0] See [1] for
>>>> another manifestation of this.
>>>>
>>>> I think calling to_python() in Model.save() would have unacceptable
>>>> performance consequences for little benefit considering that it's a
>>>> reasonable expectation for developers to provide the correct type.
>>>> Further,
>>>> you can use full_clean() to coerce to the correct types:
>>>>
>>>> m = Model(decimal='12.9')
>>>> m.full_clean()
>>>> self.assertEqual(m.decimal, Decimal('12.9'))
>>>>
>>>> What do you think? Absent a better suggestion, we could document this
>>>> pitfall so that there's something to point to when related tickets come in.
>>>>
>>>> [0] https://code.djangoproject.com/ticket/27825
>>>> [1] https://code.djangoproject.com/ticket/24028
>>>>
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>>
>>
>> --
>> Adam
>>
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