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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.

Django forms: List of checkboxes populated from a model

In Django I'm trying to render a list of checkboxes with the choices being populated from values in a model's field. Here is what I have so far:
models
#Model that feeds the list of checkboxes
class Category_Level1(models.Model):
category_level1_name = models.CharField(max_length = 50)
forms
class ProductCategoryLevel1Form(forms.Form):
product_category_level1 = forms.MultipleChoiceField(label = "Product Category", choices = Category_Level1.objects.all(), widget = forms.CheckboxSelectMultiple)
views
def select_product(request):
product_category_level1 = ProductCategoryLevel1Form()
if request.method == 'POST':
product_category_level1_form = ProductCategoryLevel1Form(request.POST)
if product_category_level1_form.is_valid():
product_category_level1_list = product_category_level1_form.cleaned_data.get('product_category_level1', 'Unk')
# Saving the selected categories to another table
product_cat_obj = Product_Category_Level1(category_level1_name = product_category_level1_list)
product_cat_obj.save()
context = {
'product_category_level1' : product_category_level1
}
return render(request, 'select_product/select.html', context)
template
<div class="row">
<label for="id_prod_category"></label>
{% product_category_level1 %}
</div>
I get the following error:
Invalid block tag on line 23: 'product_category_level1', expected
'endblock'. Did you forget to register or load this tag?
What am I doing wrong?
Appreciate any suggestions.

Django uses two types of markup - {% ... %} for tags and {{ ... }} for variables.
In this code you are trying to render the product_category_level1 variable, therefore you should use {{ product_category_level1 }} instead of {% product_category_level1 %} in your template.
However, there are also some other bugs in this code.
You seem to be mixing product_category_level1 and product_category_level1_form in your view code. These should all be the same variable. You need to use the same variable so when binding the POST data and calling is_valid() the form you display to the user contains any validations errors. As you currently have it you always give the user a new instance of the form - if any data validations fail the form will be presented again with all the fields empty and no error messages.
You need to tell Django how you want your form to be rendered - as p tags, as li tags, etc. As such you'll need to add the method call as_p like this: {{ product_category_level1.as_p }}. More rendering options can be found here: https://docs.djangoproject.com/en/1.10/topics/forms/#working-with-form-templates

Django: How to put existing fields when displaying form for UpdateView?

I'm making an episode tracker website and when I want the user to edit a show, the form provided starts with empty fields. How do I fill the form with already existing fields? For example, when a user is watching a show and is originally at episode 5, how do I call the update form with the Episode field already at 5 instead of it being empty?
views.py
class ShowUpdate(UpdateView):
model = Show
slug_field = 'title'
slug_url_kwarg = 'show'
fields = ['description', 'season', 'episode']
show-detail.html
<form action="{% url 'show:show-update' show=show.title %}" method="post">
{% csrf_token %}
<button type="submit">Edit</button>
</form>

You can fill a form with the values in an UpdateView with
def get_initial(self):
return { 'field1': 'something', 'field2': 'more stuff' }
Also the UpdateView inherits from the SingleObjectMixin, which provides get_object and get_queryset, so you could use either to get the object data you want to populate the form with. Something like:
def get_object(self):
return Show.objects.get(pk=self.request.GET.get('pk'))
Check out the docs for more info
Also, if you have a pk or slug as a parameter in your url, it should pick it up as well. Such as:
url(r'^shows/update/(?P<pk>\d+)/$',ShowUpdate.as_view())

Pre-Populate a WTforms in flask, with data from a SQLAlchemy object

I am fairly new to flask framework and was creating an edit profile page for a webportal. I am stuck at a point and am unable to autofill a form.
Here is my form class :
class EditProfile(Form):
username = TextField('Username', [Required()])
email = TextField('Email', [Required()])
about = TextAreaField('About', [Required()])
website = TextField('Website', [Required()])
This is my function that evaluates the form.
def editprofile(nickname = None):
if g.fas_user['username'] == nickname or request.method == 'POST':
form = EditProfile()
form_action = url_for('profile.editprofile')
if request.method == 'POST' and form.validate():
if form.username.data == nickname :
query = EditProfile(form.username.data,
form.email.data,
form.about.data,
form.website.data,
)
print query #debug
db.session.add(query)
db.session.commit()
flash('User Updated')
print "added"
return(url_for('profile.editprofile'))
return render_template('profile/add.html', form=form,
form_action=form_action, title="Update Profile")
else:
return "Unauthorised"
And my html template for form is form is :
{% extends "base.html" %}
{% block title %}
{{ title }}
{% endblock %}
{% block content %}
{% from "_formhelpers.html" import render_field %}
<div id="Edit Profile">
<h2>{{ title }}</h2>
<form method="post" action="{{ form_action }}">
<fieldset>
<legend></legend>
{{ render_field(form.username) }}
{{ render_field(form.email)}}
{{ render_field(form.about )}}
{{ render_field(form.website) }}
</fieldset>
<input type="submit" class="button" value="Save"/>
</form>
</div>
{% endblock %}
I have an object, of user class. And from that object I want to prefill this form.How can I prepopulate the values in the form. I am trying to implement the edit profile functionality here.

You need to pass your object to the form when you create it.
form = EditProfile(obj=user) # or whatever your object is called
You're going to run into some trouble with
query = EditProfile(form.username.data,
form.email.data,
form.about.data,
form.website.data,
)
db.session.add(query)
It creates a new instance of your EditProfile form. You then try to add it to the session. The session wants models, not forms.
Instead, after validating the form, you can associate its values with the object.
form.populate_obj(user) # or whatever your object is called
Because your object was already loaded, you won't need to add it to the session. You can remove db.session.add(query) and just call db.session.commit().

The easiest way I've found of doing this is to fill the form fields on a get request.
#decorator_authorized_user # This decorator should make sure the user is authorized, like #login_required from flask-login
def editprofile(nickname = None):
# Prepare the form and user
form = EditProfile()
form_action = url_for('profile.editprofile')
my_user = Users.get(...) # get your user object or whatever you need
if request.method == 'GET':
form.username.data = my_user.username
form.email.data = my_user.email
# and on
if form.validate_on_submit():
# This section needs to be reworked.
# You'll want to take the user object and set the appropriate attributes
# to the appropriate values from the form.
if form.username.data == nickname:
query = EditProfile(form.username.data,
form.email.data,
form.about.data,
form.website.data,
)
print query #debug
db.session.add(query)
db.session.commit()
flash('User Updated')
print "added"
return(url_for('profile.editprofile'))
return render_template('profile/add.html', form=form,
form_action=form_action, title="Update Profile")
This sets up the function to return a prefilled form on a get request. You'll have to rework the section under form.validate_on_submit. Dirn's answer suggests a few of the right things to do.

To populate the form with your SQLAlchemy object use:
form = EditProfile(obj=<SQLAlchemy_object>)
If your form fields don't match the database columns in your model for whatever reason (they should), the form class takes kwargs:
**kwargs – If neither formdata or obj contains a value for a field, the form will assign the value of a matching keyword argument to the
field, if provided.
I found that one use case for this is if you have a form that contains fields that reference more than one model (e.g. through a relationship); passing the one obj isn't enough.
So let's take your example and say that in your database model (for user) you use site instead of website (the form field name). You'd do this to populate your form from the SQLAlchemy object:
form = EditProfile(obj=user, website=user.site)
Then in the POST you'd have to do this to populate your SQLAchemy object from your form:
form.populate_obj(user)
user.site = form.website.data
db.session.commit()