Set ImageField default value to random image out of a list of images in Django

Question

I have some images inside the static directory and want to create a model that has a ImageField. I want to set the default field to any one of those images. I have tried using this -

def randomImage():
    return ImageFile('media/blog/image/' + str(random.randrange(1, 15, 1)) + '.jpg')

# ----------------------- Model for each post in the blog-------------------
class Post(models.Model):
    heading = models.CharField(max_length=150)
    author = models.ForeignKey(User)
    postBody = models.TextField()
    postDate = models.DateTimeField('posting date')
    postImage = models.ImageField(upload_to='media/blog/image/'+str(int(time.time())), default=randomImage)

Answer 1

Here I'm taking some assumptions,
1. Your default images are inside the static directory
2. Inside the static directory, all files are images

What is the major trick here ?

Django needs a valid file path only to create or update a file entry (image is also a file). So, what we're doing here is, list out all the files (assuming those are only images) and picking up one entry randomly using random.choice() and retun an absoulute path (something like static/my_img.jpg) to the default argument

import time
from random import choice
from os.path import join as path_join
from os import listdir
from os.path import isfile


def random_img():
    dir_path = 'static'
    files = [content for content in listdir(dir_path) if isfile(path_join(dir_path, content))]
    return path_join(dir_path, choice(files))


class Post(models.Model):
    # other fields
    postImage = models.ImageField(
        upload_to='media/blog/image/' + str(int(time.time())),
        default=random_img)

UPDATE-1

I've created a minimal example in Django 2.1.1 which can be found in follwing git repo
Repopsitory link -> django2X
1. clone the repository,create a virtual env and install the dependencies (provided a requirements.txt file)
2.create a new superuser or use mine (username -> admin, pass-> jerin123@)
3.run the server and login to django admin : (screenshot-1)
4. Create a new Post instance (again and again)

That's it

UPDATE-2

I've made few changes in my minimal example, which are
1. Created a simple object creation (here, the Post model object) while every django startup (checkout sample/app.py)
2. Added MEDIA_ROOT and MEDIA_URL to the settings.py file

Now, start your project (it will create 3 objects per every startup) and go to http://127.0.0.1:8000/admin/sample/post/.
Then open any instance and click on the image link (screenshot-2) and it will open the image (screenshot-3)

Answer 2

My solution is to override the model save method and check if the model is being created for the first time and also check if the postImage image field is empty. If so populate the postImage field with contents of a Radom image. Django will handle the rest

If we use the path of the Radom image directly in our model we will end up like serving some of the post model files from the media folder and some other from the static directory which is not recommended. Instead, we feed the image file content to the postImage field and Django will save the image to media folder and thus we can serve all our model images from media folder itself. Wola

Code

The following code is tested in Python 3.6 Please add the code to your models.py

from pathlib import Path
from random import randint
import time
from django.core.files import File
from django.db import models

allowed_image_extensions = ['.jpg', '.png', '.jpeg']


def get_file_extension(file_path):
    return Path(file_path).suffix


def get_files_in_directory(directory, absolute_path=False):
    from os import listdir
    from os.path import isfile
    only_files = [f for f in listdir(directory) if isfile("{}/{}".format(directory, f))]

    if not absolute_path:
        return only_files

    else:
        return ["{}/{}".format(directory, file_) for file_ in only_files]


def get_random_image_from_directory(directory_path, image_extension=None):
    files_in_directory_path = get_files_in_directory(directory_path, absolute_path=True)

    if image_extension:
        allowed_file_types = [image_extension]
    else:
        allowed_file_types = allowed_image_extensions

    # filter out files of type other than required file types
    filtered_files_list = [_file for _file in files_in_directory_path if
                       get_file_extension(_file).lower() in allowed_file_types]

   random_index = randint(0, len(filtered_files_list) - 1)
   random_file_path = filtered_files_list[random_index]
   random_file_content = File(open(random_file_path, 'rb'))

   return random_file_content


def get_post_image_path(instance, filename):
    path_first_component = 'posts'
    ext = get_file_extension(filename)
    current_time_stamp = int(time.time())
    file_name = '{}/posts_{}_{}{}'.format(path_first_component, instance.id, current_time_stamp, ext)
    full_path = path_first_component + file_name
    return full_path

class Post(models.Model):
    heading = models.CharField(max_length=150)
    author = models.ForeignKey(User)
    postBody = models.TextField()
    postDate = models.DateTimeField('posting date')
    postImage = models.ImageField(blank=True, null=True, upload_to=get_post_image_path)

    # override model save method
    def save(self, *args, **kwargs):

        # check model is new and postImage is empty
        if self.pk is None and not self.postImage:
            random_image = get_random_image_from_directory(settings.STATIC_ROOT)
            self.postImage = random_image
            random_image.close()


    super(Post, self).save(*args, **kwargs)

Also no need to set ‘/media’ in upload_to path. Django will read media path from settings variable

The best practice is to move those set of default images out of static directory to another folder probably another folder with name resources or any another meaningful name since the static directory contents will change frequently as the project grows