Re: Get datetime now, not at server initialisation

Thanks, that was very helpful. I had another pointer on this and
found out that the easiest way to do this is just to change the
```file``` line in the class to:

```
file = ImageField(_('image'), upload_to='images/items/%Y/%m/%d/%
H/%M/%S')
````

There are a few things that I do not understand, however, after
playing around with some code for a while.

If I just pass a string to ```file``` it understands that this is a
partial path, and it has to stick ```filename``` on the end. eg:

```file = ImageField(_('image'), upload_to='images/items')```

Likewise with the version above with the date formatting.

This is also the case when I used my initial ```upload_path```
function, calling it with ```upload_to=upload_path()``` – but this
did not suit the task, because ```upload_path``` loaded at
initialisation of the server.

So, given that ```upload_path``` returns a string, I don't understand
why I also have to concatenate the ```filename```:

```
def upload_path(instance, filename):
dtnow = datetime.now(timezone.utc)
dtstr = '{:%Y/%m/%d}'.format(dtnow)
dtstr = 'images/items/' + dtstr + '/' + filename
return dtstr
```
In this case, if I do not concatenate ```filename``` then the
uploaded file gets named with the last element of the date formatting
and without a file extension, ie potentially like this:

```images/items/2020/10/28/20/59/55```

rather than:

```images/items/2020/10/28/20/59/55/image.jpg```

The other thing I don't understand is how ```instance``` and
```filename``` are passed to the function ```upload_path```. I would
expect to do something like:

``` file = ImageField(_('image'), upload_to=upload_path(instance,
filename))```

But if I do that I get:

```NameError: name 'instance' is not defined```

Sorry for so many more questions!


-- Clive

On 28 Oct 2020, at 08:58, Carles Pina i Estany wrote:

>
> Hi,
>
> On Oct/27/2020, Clive Bruton wrote:
>
>> I have a function that uses the current date to set up a file path
>> for
>> uploaded images:
>>
>> ********************
>>
>> def upload_path():
>
> [...]
>
>> class Image(models.Model):
>> item = models.ForeignKey(Item, on_delete=models.CASCADE)
>> #file = ImageField(_('image'), upload_to='images')
>> file = ImageField(_('image'), upload_to=upload_path())
>
>
>> The problem is that when the Image class calls 'upload_path' the
>> datetime portion of this is always the runserver initialisation time,
>> rather than the time when 'upload_path' is called/used.
>>
>> How to fix this?
>
> For what I remeber (I use FileField usually but this is noto
> relevant I
> hope) you should do:
>
> def upload_path(instance, filename):
> # you have access to the instance (object model Image in your
> case)
> # and the filename that the user used to upload it
> # and this is executed on the upload time
> return your_new_file_name
>
> In the model:
> file = ImageField(_('image'), upload_to=upload_path)
>
> note that upload_path is a callable: it gets called on the upload
> time.
> In your code it was called on initialization time.
>
> Some time ago I had a similar code that caused a bug: in a ListView
> the
> "queryset = " is executed on startup time. For a dynamic one I should
> have used get_queryset() method.
>
> --
> Carles Pina i Estany
> https://carles.pina.cat
>
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