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Operation of standard Django view, form and template code to update a model

I am trying to understand how a very regularly used code-form in Django views.py actually works. I see the following (or a variation) used a lot, but I can’t find a line-by-line explanation of how the code works – which I need if I am to use it confidently and modify when needed.
Can you let me know if I have understood how Django processes these various components? If not, please indicate where I have misunderstood.
I will start with the model then introduce urls.py the view and the form. I will go through the relevant parts of the code. I will consider:
The model:
#models.py
class CC_Questions(models.Model):
# defining choices in Model : https://docs.djangoproject.com/en/4.0/ref/models/fields/
personality = [
('IF','IF'),
('IT','IT'),
('EF','EF'),
('ET','ET'),
]
q_text = models.CharField('Question text', max_length=200)
#C1_Type = models.CharField('Choice 1 Type', max_length=2)
C1_Type = models.CharField(choices=personality, max_length=2)
Choice1_text = models.CharField('Choice 1 text', max_length=100)
#C2_Type = models.CharField('Choice 2 Type', max_length=2)
C2_Type = models.CharField(choices=personality, max_length=2)
Choice2_text = models.CharField('Choice 2 text', max_length=100)
#
def __str__(self):
return self.q_text[:20]
The url
#
#urls.py
app_name = ‘polls’
urlpatterns = [
…..
# ex: /polls/p2create
path('p2create/', p2_views.p2create, name='p2create'),
…
The view:
#views.py
from.forms import Anyform
#
def p2create(request):
if request.method == 'POST':
form = AnyForm(request.POST)
if form.is_valid():
form.save()
return redirect('/polls/p2')
else:
form = AnyForm()
context = {'form' : form}
return render(request, 'pollapp2/create.html', context)
#
The form:
#forms.py
#
….
from django import forms
from .models import ….. CC_Questions …
…….
class AnyForm(forms.ModelForm):
class Meta:
model = CC_Questions
fields = ['q_text', 'Choice1_text', 'Choice2_text','C1_Type','C2_Type']
The template:
#
# Create.html
#
…..
{% load widget_tweaks %}
…..
<form method="POST">
{% csrf_token %}
…
<div class="row">
<div class="col-lg-5">
<div class="form-group">
<label for="Choice1_text ">Choice 1</label>
{% render_field form.Choice1_text class="form-control" %}
<label for="C1_type">Type 1</label>
{% render_field form.C1_Type class="form-control" %}
…….
Does the code operate as follows?
The user enters URL in browser: http://localhost:8000/polls/p2create/
The urls.py picks the view to execute
path('p2create/', p2_views.p2create, name='p2create'),
views.py runs the view:
def p2create(request):
Now, as no form has yet been "identified" or "loaded" (??) the following test fails:
if request.method == 'POST':
so the Else clause executes
else:
form = AnyForm()
that "sets" the variable form to "AnyForm()"
The following line creates a dictionary, named context, that creates a key 'form' that is linked with the value form (=Anyform)
context = {'form' : form}
The following line searches for create.html in the template directory, passing the directory context as a parameter
return render(request, 'pollapp2/create.html', context)
Then template, create.html, displays various input boxes (??) from :
<label for="Choice1_text ">Choice 1</label>
{% render_field form.Choice1_text class="form-control" %}
When the submit button is pressed on the displayed page, this "passes back" (??) the {% render_field .. %} values to the view (?????)
<form method="POST">
...
<div class="col-lg-4">
<button type="submit" class="btn btn-info">Submit</button>
</div>
...
</form>
the view is executed again (????) , but this time request method is set to "POST" because of the form method="POST" in the template (?????)
if request.method == 'POST':
Now the same form , AnyForm , is "reloaded" (????) but with the parameter value "POST"
if request.method == 'POST':
form = AnyForm(request.POST)
Now if the form is valid (I have no idea what a "valid" or "invalid" form is)
if form.is_valid():
then all the values "captured" in the template by (???)
<label for="Choice1_text ">Choice 1</label>
{% render_field form.Choice1_text class="form-control" %}
(??????)
are written by the view (?????)
form.save
to the corresponding fields in the ModelForm (?????)
class Meta:
model = CC_Questions
fields = ['q_text', 'Choice1_text', 'Choice2_text','C1_Type','C2_Type']
The view then redirects and loads the home page in the browser
return redirect('/polls/p2')

Ok, So with the help of the references (mentioned below) and the workflow suggested by you, let us first see, the Django MVT workflow and then address the various questions asked in between the post.
WebForms with Django MVT in brief:
Prepare data of several different types for display in a form.
Render data as HTML.
Edit, enter data using a convenient interface.
Validate and clean up the data.
Return data to the server.
Save, delete or pass on for further processing.
The URL:
When a user requests a page from your Django-powered site, this is the algorithm the system follows to determine which Python code to execute. Which is handled by our views.py. From the frontend, if the request is not 'POST', then it is a GET request, hence the else part of the handling function in the views.py executes. This you have mentioned already.
The View: - Form data sent back to a Django website is processed by a view, generally, the same view which published the form. This allows us to reuse some of the same logic. To handle the form we need to instantiate it in the view for the URL where we want it to be published.
If we use request.POST, as in this line:
form = AnyForm(request.POST)
It transforms the form into a bound form (Form bound with data). Read more about it here.
Questioned By You (QBY) - When the submit button is pressed on the displayed page, this "passes back" (??) the {% render_field .. %} values to the view (?????)
So, yes, If the action attribute is not mentioned in the form then the data will be passed to the view responsible for displaying the form.
QBY - the view is executed again (????), but this time request method is set to "POST" because of the form method="POST" in the template (?????)
The button type submit, submits the form and make the request a POST request. The Django template sends that submitted data in the request.POST.
QBY - Now the same form, AnyForm, is "reloaded" (????) but with the parameter value "POST"
Here, if the return method at the end of the POST condition is HttpResponseRedirect it will redirect the user to the mentioned URL page, but if the same HTML is used to be rendered then the form will be displayed as a bound form. (It depends upon the requirements)
QBY - Now if the form is valid (I have no idea what a "valid" or "invalid" form is)
Form.is_valid()
The primary task of a Form object is to validate data. With a bound Form instance, call the is_valid() method to run validation and return a boolean designating whether the data was valid. If yes, then the data is being saved in the model.
QBY - then all the values "captured" in the template by (???)
All the values are sent to views in the request.POST. We can check it by
print(request.POST)
QBY - are written by the view (?????), form.save to the corresponding fields in the ModelForm (?????)
Save method is called on the Django ModelForm instance in order to save the data to the database. Calling save would run the validation check. A ValueError will be raised if the data in the form doesn't validate.
This saved data can now be processed further.
References:
[https://docs.djangoproject.com/en/4.0/topics/forms/][2]
[https://www.tangowithdjango.com/book/chapters/models_templates.html][3]
[https://docs.djangoproject.com/en/4.0/ref/forms/api/][4]

Clean Django form fields with same name

I have a django template in which I'm dynamically rendering multiple fields (using ajax)
Below is a Django form (which has been rendered in a template) whose fields have same names. I want to use the cleaned_data method to clean form data in views.py before storing them in the database.
index.html
<div class="form-container">
<!-- ASSUMING I HAVE ALREADY ADDED FIELDS DYNAMICALLY -->
<form id = "orderForm" action="newPickupOrder/" method="post" name="processForm">
<input type='text' name='this_field'>
<input type='text' name='this_field'>
<button type="submit">Submit</button>
</form>
</div>
<form id="addItemForm">
{% csrf_token %}
<!-- BUTTON TO ADD MORE FIELDS DYNAMICALLY -->
<button id = "addItemButton">Add item</button>
</form>
<script>
var addItemButton = document.querySelector('#addItemButton');
addItemButton.onclick = function(){
$.ajax({
type: 'POST',
url: 'addItem/',
data: addItemForm.serialize(),
success: function (response) {
$("#orderForm").append(response);
console.log('Success');
},
error: function (response) {
console.log('Error = '+response);
}
});
};
</script>
forms.py
class ItemForm(forms.Form):
this_field = forms.CharField()
urls.py
urlpatterns = [
url(r'^newPickupOrder/$', views.pickup_order_view, name='new_pickup_order'),
]
views.py
def add_item(request):
if request.method == 'POST':
itemForm = ItemForm()
return HttpResponse(itemForm.as_p())
def pickup_order_view(request):
if request.method == 'POST':
form = ItemForm(request.POST)
same_name_fields = request.POST.getlist('this_field')
# WANT TO CLEAN DATA IN same_name_fields
if form.is_valid():
print(form.cleaned_data)
# ONLY PRINTS THE LAST FIELD's DATA
return HttpResponseRedirect('/viewPickupRequests')
The problem I'm facing is that if I use form.cleaned_data['this_field'], only the last field's data is fetched i.e. in this example, the field with value anotherTestValue is fetched and cleaned. If I fetch the data using request.POST.getlist('this_field'), all the fields' data is fetched and stored as a list, but, I don't know how to clean it using cleaned_data method. Is there a way to apply the cleaned_data method to the list of field data?

I'm sorry, I can't test if this works so this is not really an answer - but the comment system is not suitable for larger code chunks so I'm posting here.
Django forms lack a field type that renders to multiple text inputs with the same name. The proper thing to do would be to write a new form field class and a new widget. Since you are not rendering the form in the template (you are using it only for validation) I will omit the widget part.
class AcceptAnythingMultipleChoiceField(forms.MultipleChoiceField):
def validate(self, value):
if self.required and not value:
raise ValidationError(
self.error_messages['required'],
code='required'
)
Then use this field class instead of forms.CharField() (you may need to pass an empty choices parameter).
[update]
So essentially what you're saying is that I need to create new form field class and then render it to the template each time the user wants to add a new field? What if user has to add 15 fields, I'll need to create 15 classes then! I think this method won't be suitable in scenarios where number of fields required to be generated is large. I feel there should be some elegant way to do this which i'm not aware of – The OP
No, it is not what I'm saying. You probably want to subclass something like MultipleHiddenInput and set AcceptAnythingMultipleChoiceField.widget to it. You will have to create a new template based on the template for MultipleHiddenInput and replace input type="hidden" for type="text" (the original template is django/forms/widgets/multiple_hidden.html).
class AcceptAnythingWidget(MultipleHiddenInput):
template_name = 'django/forms/widgets/multiple_visible.html'
class AcceptAnythingMultipleChoiceField(forms.MultipleChoiceField):
widget = AcceptAnythingWidget
def validate(self, value):
if self.required and not value:
raise ValidationError(
self.error_messages['required'],
code='required'
)
This should render as many <input name='this_field'> as needed for instantiated forms at the frontend if you use:
{{ form.this_field }}
in the template, but will not add/remove them dynamically.
In order to do that you must plug in the JavaScript required to add/remove inputs dynamically in the widget but I will left this as an exercise for you. Look at Form Assets (the Media class) in the docs in order to figure out how to do that.

I think that what you are looking for is formsets. https://docs.djangoproject.com/en/2.0/topics/forms/formsets/
from django.forms import formset_factory
ItemFormSet = formset_factory(ItemForm, extra=2)
You can the essentialy use ItemFormSet in the way you would use a normal form except that this objects is iterable.
You will also have to change your jquery if you want to dynamically add items. There are many examples online on how to do this. In short what you do is
clone one of the forms in the formset
clear all the values from the copied form
update the input's (prefixes of) id's
Using Formsets doesn't solve the problem of fetching and validating
fields with same name. The issue still remains
It does however generate the end result you wanted (see below). My question would be why you need to have inputs with the same name? If there is some jquery stuff that uses these names I dont see any reason why you wouldn't be able to use name like... or assign a class to the inputs instead.
def pickup_order_view(request):
if request.method == 'GET':
ItemFormSet = formset_factory(ItemForm, extra=5)
item_formset = ItemFormSet()
template = "some_template.html"
template_context = {'item_formset': item_formset}
return render(request, template, template_context)
if request.method == 'POST':
ItemFormSet = formset_factory(ItemForm)
item_formset = ItemFormSet(request.POST)
same_name_fields=[]
if item_formset.is_valid():
for item_form in item_formset:
same_name_fields.append(item_form.cleaned_data['this_field'])
print(same_name_fields)
Template
<form id = "orderForm" action="newPickupOrder/" method="post" name="processForm">
{% csrf_token %}
{{ item_formset.management_form }}
{{ for item_form in item_formset }}
{{ item_form.as_p }}
{{ endfor }}
<input type='submit' value='submit'>
</form>
Go to newPickupOrder/ , fill in the 5 fields, hit submit, and watch it print your list.

Calling a field from a model in template other than url pattern not working

I'm new to Django and programming. I'm trying to call the field from a model through a template other than specified in my url patterns but I keep on getting a blank display in the div block I want i to display in. I want a list of categories to be displayed in the left side-bar. I have looked at many answers on SO Django foreign key relation in template and How to display one field from a model in Django template and Ive worked through the Django docs.
I've created a list of categories in the admin class. The code is working as intended but Im not able to extend this list to be displayed from the base.html template class so that I have category navigation throughout.
I have two models:
class Post(models.Model):
category = models.ForeignKey(Categories, related_name='topic')
...
class Categories(models.Model):
topics = models.CharField(max_length=100)
...
Here is my view which works in the 'categories.html' template
def categories(request):
category = Categories.objects.all()
return render(request, 'posts/categories.html', {"category": category})
The url pattern related to it
url(r'^categories/$', views.categories, name='category'),
Here is how i'm calling the field
{% for field in category %}
<div class="col-sm-10">{{ field.topics }}</div>
{% endfor %}
I've tried alot of different approaches such as:
{% for field in category.topic.all %}
{% endfor %}
Please assist. Thank you in advance.

Initializing form input fields from url parameters in Django

I am building my own projects based on the instructions from 'Django by Example' book.
However I got stuck on how does django initialize input form fields using URL parameters?
#models.py
class Image(models.Model):
title = models.CharField(max_length=200)
description = models.TextField(blank=True)
url = models.URLField()
(...)
#views.py
def image_create(request):
if request.method == 'POST':
form = ImageCreateForm(data=request.POST)
(...)
else:
form = ImageCreateForm(data=request.GET)
return render(request,
'create.html',
{'form': form})
#forms.py
class ImageCreateForm(forms.ModelForm):
class Meta:
model = Image
fields = ('title', 'url', 'description')
widgets = {
'url': forms.HiddenInput,
}
#create.html
{% extends "base.html" %}
{% block content %}
<h1>Bookmark an image</h1>
<img src="{{ request.GET.url }}" class="image-preview">
<form action="." method="post">
{{ form.as_p }}
{% csrf_token %}
<input type="submit" value="Bookmark it!">
</form>
{% endblock content %}
I could not find any specific line of code which would explicitly tell to get request.GET parameters and assign each of them to corresponding input field.
I assume that all of this has to do with the form initialization on line: form = ImageCreateForm(data=request.GET) in views.py
Questions:
Can someone please explain me how does django use request.GET parameters to initialize input fields values(assigns them URL parameters' values)?
Does it simply match, for every request.GET key, the corresponding input field 'name' attribute, and then assigns to that particular input field the value corresponding to the key in request.GET?
Also can someone confirm if there is a relationship between the model/form(which one?) field names to the URL parameters?
What is the difference between these two(as both of them seems to work the same way, except the latter returns list in the input field values):
form = ImageCreateForm(data=request.GET)
form = ImageCreateForm(initial=request.GET)

1) Yes - request.GET is simply a fancy dictionary (technically a QueryDict), and the form "data" argument expects a dict with keys corresponding to the fields in the form. You could technically pass the form any dictionary if it had the right keys representing the fields.
2) Generally speaking, there is no relation between model/form fields and url parameters. However, if you are using certain Class Based Views (such as a DetailView) if you set a slug or id in your url, it will pass the value along to the view and map it to the objects slug or id. The get_object() method in the link below has an example.
https://ccbv.co.uk/projects/Django/1.9/django.views.generic.detail/DetailView/
3) The data attribute to a form is what is submitted (usually POSTed) to the form whereas the initial value is what is passed to the form upon first page load. For example, if you were editing an object, typically the existing object data would populate the initial value. Then, if you POSTed edits to the form, it would be passed in as data.

A way to render content to a base template

I have a base template which contains header, footer and a block "content" which then I override in different CBVs.
There is little "user-space" divinside a header where I want to keep user's info in case he is logged in and a login form if he is a guest.
Right now the only way that comes in mind is to create a django app and use it as a tag. But I think there is a better solution. Because as far as I know tags can slow down django project in future.
Also I think that maybe I would like to manipulate this div from a view which renders a child template. For example I calculate and display some value on a page but also I want to display it in a "user-space" div as well. I think this can be achieved by pushing data to the user's session and then using this while rendering "user-space" div from another code.

Assuming you have django.contrib.auth.user in your INSTALLED_APPS, you can access the user's login status using user.is_authenticated():
{% if user.is_authenticated %}
<div>Welcome back, {{ user.username }} | <a href='/logout/'>Logout</a></div>
{% else %}
<div>
<form action='/login/' method='POST'>
{{ csrf_token }}
{{ login_form }}
<input type='submit'>
</form>
</div>
{% endif %}
Edit:
In response to your comment:
Let's suppose client does a POST request by which we calculate some number - total price. And I need to display it in that div.
As documented
Define your view:
from django.shortcuts import render
from .forms import MyForm
def simple_view(request):
if request.method == 'POST':
# create a form instance and populate it with data from the request:
form = MyForm(request.POST)
# check whether it's valid:
if form.is_valid():
# process the data in form.cleaned_data as required
result = form.cleaned_data['some_input'] * 50
return render(request, 'my_template.html', {'result': result})
# if a GET (or any other method) we'll create a blank form
else:
form = MyForm()
return render(request, 'my_other_template.html', {'form': form})
Display result in your template:
<!-- my_template.html -->
<div>{{ result }}</div>
Maybe you need to be more specific with your question, this is what I think you are looking for though. You should put logic like you are describing into a view, not a template.