Reusable_functions_in_django

## in utils.py file write the following
from django.apps import apps
from django.db import models
from django.core import exceptions

##### check if field is exists or not
@classmethod
def model_field_exists(cls, field):
   try:
     cls._meta.get_field(field)
     return True
  except exceptions.FieldDoesNotExist:
     return False
models.Model.field_exists = model_field_exists


########### For Adding ....
def adding(
    request,
    form_class, app_name, model_name,
    url, template_path, related_field=None,
    user=None, field_1=None,
    field_2=None, field_3=None,
    context={}
):
    if request.method == 'POST':
        form = form_class(
            request.POST or None,
            request.FILES or None,
            user=user, f1=field_1, f2=field_2
        )
        if form.is_valid():
            save_form = form.save(commit=False)
            save_form.save()
            messages.success(request,
                'Adding new (' + str(model_name) + ') done successfully') #
            return redirect(reverse(url, args=(save_form.id,)))
        else:
            messages.error(request,
                'Add new (' + str(model_name) + ') failed ' )
            return redirect(request.META.get('HTTP_REFERER', ''))
    else:
        form = form_class(user=request.user, f1=field_1, f2=field_2)
        return render(request, template_path, context=({'form':form,} | context))

###
def editing(
    request,
    id_field,
    form_class, app_name, model_name,
    url=None, template_path=None, related_field=None,
    user=None, field_1=None, field_2=None, field_3=None,
    context={}
):
    cls = apps.get_model(app_name, model_name)
    qs = cls.objects.select_related(related_field).get(id=id_field)
    if cls.field_exists('user'):
        user = qs.user
        print('User exists or not ==>> ', cls.field_exists('user'))
    else:
        user=None

    print('User exists or not ==>> ', cls.field_exists('user'))

    form = form_class(
            request.POST or None,
            request.FILES or None,
            user=user,
            f1=field_1,
            f2=field_2,
            instance=qs
        )
    if form.is_valid():
        save_form = form.save()
        save_form.save()
        messages.success(
            request, 'Save changes to (' + str(model_name) + ') done successfully')
        return redirect(reverse(url, args=(save_form.id,)))

    return render(request, template_path, context=({'form':form,} | context))

## Then you can use it in views.py as follows
from your_project_name.utils import adding, editing
def add_inventory(request, pro_id):
    product = Product.objects.only().get(id=pro_id)
    # print(product)
    context = {
        'product': product,
    }
    return adding(
        request,
        form_class=InventoryForm,
        app_name='inventories',
        model_name='Inventory',
        url='edit_inventory',
        template_path='inventories/add_inventory.html',
        user=request.user,
        field_1=product,
        field_2=None,
        field_3=None,
        context=context
    )


def edit_inventory(request, inv_id):
    qs = Inventory.objects.select_related('product').get(id=inv_id)
    context={
        'qs':qs
    }
    return editing(
        request,
        id_field=inv_id,
        form_class=InventoryForm,
        app_name='inventories',
        model_name='Inventory',
        url='edit_inventory',
        template_path='inventories/edit_inventory.html',
        # user=None,
        field_1=qs.product,
        field_2=None,
        field_3=None,
        context=context
    )

#### forms.py
class InventoryForm(forms.ModelForm):
    class Meta:
    model = Inventory
    fields = [
        'user',
        'product',
        'quantity',
        'reserved_quantity',
        'available_quantity',
    ]

    def __init__(self, *args, user, f1, f2, **kwargs):
    self.user = user
    self.product = f1
    super(InventoryForm, self).__init__(*args, **kwargs)
    self.initial['user'] = self.user
    self.initial['product'] = self.product

########################################