How to fix adding images via form?

Question

Django

Hello, I have two forms - "Create" and "Edit". In the create form, the image is attached, but not in the edit form, while the framework does not give any errors.
Please tell me where to dig? Maybe there are some subtleties in working with images that I don't know about?
Create form listing

def post_new(request):
    if request.method == "POST":
        form = PostForm(request.POST)
        if form.is_valid():
            farm = form.save(commit=False)
            farm.owner = request.user
            farm.published_date = timezone.now()
            farm.save()
            return redirect('blog.views.post_detail', id=post.id)
        else:
            post = PostForm()
            return render(request, 'posts/post_edit.html', {'form': form})

Edit form listing

def post_edit_main(request, id):
    post = get_object_or_404(Post, id=id)
    if request.method == "POST":
        form = PostEditMain(request.POST, instance=post)
        if form.is_valid():
            post = form.save(commit=False)
            post.owner = request.user
            post.published_date = timezone.now()
            post.save()
            return redirect('post.views.own_farm_detail', id=farm.id)
    else:
        form = PostEditMain(instance=farm)
    return render(request, 'posts/post_edit_main.html', {'form': form})

Model

class Post(models.Model):
owner = models.ForeignKey('auth.User')
title = models.CharField(max_length=100,verbose_name=u'Название')
image = models.ImageField(upload_to="{{ MEDIA_ROOT }}",
verbose_name=u'Заглавное фото', help_text='Большое', blank=True, null=True)

Sample

<form method="POST" class="post-form">{% csrf_token %}
            {{ form|bootstrap}}
            <button type="submit" class="save send">Save</button>
        </form>

I was sinning on CHMOD, but when creating an image, it is attached, but when editing it is not (

Answer 1

1. 
   post = get_object_or_404(Post, id=id)
   but
   form = PostEditMain(request.POST, instance= farm )
   In the template, add enctype="multipart/form-data" to the form declaration
   request.FILES add to the form parameters after all.
   upload_to is equal to MEDIA_ROOT by default, can be omitted. And the upload_to="{{ MEDIA_ROOT }}" construct is a guaranteed problem.
   

Answer 2

PostEditMain(request.POST, request.FILES, instance=farm)