[Django]-How to use Django ImageField, and why use it at all?

1) Why use an ImageField at all? Or rather, why use a FileField?

It’s convenient for quick-and-easy forms and convenient for inserting
to Django templates.

But are there any substantial reasons, eg. Is it evidently secured against exploits and malicious uploads?

Yes. I daresay your own code probably does it too, but for a newby using the FileField will probably ensure that your important system files are not getting overwritten by a malicious upload.

2) How to write to the field file?

In your situation you would need to use a special storage backend that makes it possible to write directly to the Amazon S3. As you know, the storage backend for FileFile and ImageField are plugable. Here is one example plugin: `http://django-storages.readthedocs.io/en/latest/backends/amazon-S3.html

There is sample code which demonstrates how it can be written to. So I wll not go into that.`

3) How to try saving with a specific filename, then try again with a new filename if that randomly generated filename already exists?

ImageField and FileField takes care of this for you automatically. It will create a new filename if the old one exists. The code in my answer here did that automatically when I called it over and over again. here are some sample filenames produces (input being bada.png)

"4", "media/bada.png"
"5", "media/bada_aH0gV7t.png"
"7", "media/bada_XkzthgK.png"
"8", "media/bada_YzZuwDi.png"
"9", "media/bada_wpkasI3.png"

4) In the models.py pre_save and post_save signals and in the actual model’s save(), how can I tell if a file came in with the request?

Your instance.pk will be None

If this is a modification to an existing file the PK will be set.

---

If this is a new image upload in the pre_save

Took me forever to learn how to save an image using ImageField. Turns out it’s crazy easy — once you know how to do it, it is, at least. I mean, it all comes together sensibly after you see it.

So basically, you’re working with a FileField. I already looked into the differences between ImageField and FileField:

• ImageField takes everything FileField takes in terms of attributes,
  but ImageField also takes a width and height attribute if indicated.
  ImageField, unlike FileField, validates an upload, making sure it’s
  an image.

Using ImageField comes down to most of the same constructs as FileField does. The biggest things to remember:

request.FILES['name_of_model']

So a form is generated from something in forms.py (or wherever your forms are) like this:

imgfile         =   forms.ImageField(label = 'Choose your image',  
                                          help_text = 'The image should be cool.')

In the model, you might have this in correspondence:

imgfile = models.ImageField(upload_to=’images/%m/%d’)
So there will be a POST request from the user (when the user completes the form). That request will contain basically a dictionary of data. The dictionary holds the submitted files. To focus the request on the file from the field (in our case, an ImageField), you would use:

request.FILES['imgfield']

You would use that when you construct the model object (instantiating your model class):

newPic = ImageModel(imgfile = request.FILES['imgfile'])

To save that the simple way, you’d just use the save() method bestowed upon your object (because Django is that awesome):

if form.is_valid():  
        newPic = Pic(imgfile = request.FILES['imgfile'])
        newPic.save()

Your image will be stored, by default, to the directory you indicate for MEDIA_ROOT in settings.py.

The tough part, which isn’t really so tough when you catch on, is accessing the image.

In your template, you could have something like this:

<img src="{{ MEDIA_URL }}{{ image.imgfile.name }}"></img>

Where {{ MEDIA_URL }} is something like /media/, as indicated in settings.py and {{ image.imgfile.name }} is the name of the file and the subdirectory you indicated in the model. “image” in this case is just the current image in a loop of images you might create to access each image in the database:

{% for image in images %}

{% endfor %}

Make SURE you configure your urls properly to handle the image or the image won’t work. Add this to your urls:

urlpatterns += patterns('',  
        url(r'^media/(?P<path>.*)$', 'django.views.static.serve', {
            'document_root': settings.MEDIA_ROOT,
        }),
   )