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How to replace Foreign Key with Many To Many in Django models without broking whole app?

I want to change my Foreign Key to Many To Many field to let the user select multiple categories in a dropdown list.
This is what I already have. After I change Foreign Key to Many To Many I'm getting milion errors, I have to get rid of on_delete=models.CASCADE which is a core of my app. What can I do? Which way should I take? Maybe add another model? I'm so confused, especially when I am a Django newbie. Thank you for your help!
MODELS
class Category(models.Model):
name = models.CharField(max_length=50, unique=True)
def __str__(self):
return f'{self.name}'
class Expense(models.Model):
class Meta:
ordering = ('date', '-pk')
category = models.ForeignKey(Category, null=True,blank=True, on_delete=models.CASCADE)
name = models.CharField(max_length=50)
amount = models.DecimalField(max_digits=8,decimal_places=2)
date = models.DateField(default=datetime.date.today,db_index=True)
def __str__(self):
return f'{self.date} {self.name} {self.amount}'
The clue of the application is to let the user create a category e.g "PC". Then add some expenses like "GPU", "CPU" etc... and let the user link it to the "PC" category. And when the user wants to delete certain categories, all the expenses linked to it, gonna be deleted too. And this is the thing I have already did. BUT NOW I want to let the user search the main table of expenses by multiple categories. And here comes my problem, I don't have a clue how to do it and keep the whole application in one piece with all the functionalities.
SCREENSHOTS:
Categories View with just added PC category
Expense Add View

I don't think there is a simple answer to your question, but here are some resources that might help. First, I don't think you should change your models. From the way you described your application, I think a foreign key model with on_delete=CASCADE is good. The basic idea here is that you need to change your list view function so that it performs a query of your database. Also modify your template.html to include a search bar.
https://github.com/csev/dj4e-samples/tree/master/well
https://www.dj4e.com/lessons/dj4e_ads4
Modify Your List View To Allow The Searching
This is an example of a list view that allows you to search for a single term, and returns anything in the database that matches from any field. This isn't what you want to do exactly, but if you can get this working then you can modify the search conditions for your specific application. What is going on in the code below is that instead of return every item in my Ad table in my SQL database, I filter it based on the search. Then, I pass "ad_list" to the template view. Since I already filtered ad_list based on the search, in the template view it will only list the items that match. This is based on the DJ4E course, and you can watch the video there to get an idea of how he implements the search bar better.
from ads.models import Ad
from django.views import View
from django.shortcuts import render, redirect, get_object_or_404
from django.urls import reverse_lazy, reverse
from django.http import HttpResponse
from django.core.files.uploadedfile import InMemoryUploadedFile
from django.contrib.humanize.templatetags.humanize import naturaltime
from ads.utils import dump_queries
from django.db.models import Q
class AdListView(ListView):
# By convention:
template_name = "ads/ad_list.html"
def get(self, request) :
strval = request.GET.get("search", False)
if strval :
# Simple title-only search
# objects = Ad.objects.filter(title__contains=strval).select_related().order_by('-updated_at')[:10]
# Multi-field search
query = Q(title__contains=strval)
query.add(Q(text__contains=strval), Q.OR)
objects = Ad.objects.filter(query).select_related().order_by('-updated_at')[:10]
else :
# try both versions with > 4 posts and watch the queries that happen
objects = Ad.objects.all().order_by('-updated_at')[:10]
# objects = Ad.objects.select_related().all().order_by('-updated_at')[:10]
# Augment the post_list
for obj in objects:
obj.natural_updated = naturaltime(obj.updated_at)
ctx = {'ad_list' : objects, 'search': strval}
retval = render(request, self.template_name, ctx)
dump_queries()
return retval;
Modify Your Template.html to include a search bar
<form>
<input type="text" placeholder="Search.." name="search"
{% if search %} value="{{ search }}" {% endif %}
>
<button type="submit"><i class="fa fa-search"></i></button>
<i class="fa fa-undo"></i>
</form>
PS, I think you can answer your own question better when you figure it out, so help others and post it!

Problem with ManyToManyField in other model's forms using Bootstrap

I would like to show possible choices from ManyToManyField (which I have in Homes model) in the Owners form. I have Owners <--Many2Many--> Homes with custom class HomesOwners. In Homes it works out of the box, I don't know how to make it work in Owners.
I am using Django 2.2.4 with Bootstrap 4 and Postgresql. I started my project based on django-bookshelf project (also just Django and Bootstrap4). I do not use any render. Comment in django-bookshelf project mentioned How to add bootstrap class to Django CreateView form fields in the template?, so I stick to that if it comed to forms.
I'm pretty new to Python (so Django too) and web technologies in general. I googled dozen of different questions/answers but I couldn't find any nice explanation of what is what and how to use it in real life. Most of them ended up with basic usage.
I did some experimentation on my own, but no success so far...
Here is the code
I have two models - Homes/models.py and Owners/models.py
Homes/models.py:
class Homes(models.Model):
id = models.AutoField(primary_key=True)
# other fields
some_owners = models.ManyToManyField(Owners, through='HomesOwners', through_fields=('id_home', 'id_owner'), related_name='some_owners')
# end of fields, some other code in the class like "class Meta" etc.
class HomesOwners(models.Model):
id = models.AutoField(primary_key=True)
id_home = models.ForeignKey(Homes, models.DO_NOTHING, db_column='id_home')
id_owner = models.ForeignKey('owners.Owners', models.DO_NOTHING, db_column='id_owner')
Owners/models.py do not have anything special, no imports from my Homes/models.py etc.
and my forms:
Homes/forms.py:
class HomesForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(HomesForm, self).__init__(*args, **kwargs)
self.fields['some_field_from_homes_model'].widget.attrs = {'class': 'form-control '}
#
# --> no need self.fields for M2M, Django does the work
#
# but I tried also and have a --> Question 2
# self.fields["some_owners"].widget = forms.widgets.CheckboxSelectMultiple()
# self.fields["some_owners"].queryset = HomesOwners.objects.all()
Without any code as "self.fields" for M2M field, Django is able to generate for me list of owners.
Question 1
I would like to get list of Homes in my OwnersForms.
I do not know what to add. I assume that I cannot add
# Owners/models.py
some_homes = models.ManyToManyField(Homes, through='HomesOwners', through_fields=('id_home', 'id_owner'), related_name='some_homes')
because of circular import, am I right?
How do I get my Homes list using self.fields?
What do I need to add to my code?
Question 2
When I've added
# Homes/forms.py
self.fields["some_owners"].widget = forms.widgets.CheckboxSelectMultiple()
self.fields["some_owners"].queryset = HomesOwners.objects.all()
I got
<!-- html page -->
HomesOwners object (1)
HomesOwners object (2)
<!-- and so on... -->
How can I just list Owners?
How to filter/order them so first they would appear Owners not connected to any Home?
Question 3
class HomesOwners(models.Model):
id = models.AutoField(primary_key=True)
id_home = models.ForeignKey(Homes, models.DO_NOTHING, db_column='id_home')
id_owner = models.ForeignKey('owners.Owners', models.DO_NOTHING, db_column='id_owner')
def __str__(self):
return pass #return something
I can't get my head around this. This class connects Homes and Owners. When I'm thinking of Homes I would like to return Owners and vice versa. So it should return different things depending on what object we are using (home or owner). I think this is connected to my 2nd question about:
HomesOwners object (1)
Also...
In homes.html I'm using my M2M like that:
{% for owner in homes.homesowners_set.all %}
{{ owner.id_owner.id }}
{% endfor %}
I would like to write something similar to my owners.html and list homes. This is connected to my previous question, I would like to have full answer if that's possible.
EDIT
With the answer given to me I was able to add Homes to OwnerUpdate view. I have views like that:
owners/views.py
# List View
class OwnersList(ListView):
model = Owners
# Detail View
class OwnersView(DetailView):
model = Owners
# Create View
class OwnersCreate(CreateView):
model = Owners
form_class = OwnersForm
# Setting returning URL
success_url = reverse_lazy('owners_list')
# Update View
class OwnersUpdate(UpdateView):
model = Owners
form_class = OwnersForm
success_url = reverse_lazy('owners_list')
# Delete View
class OwnersDelete(DeleteView):
model = Owners
success_url = reverse_lazy('owners_list')
What change do I need to make to be able to show in OwnersList Homes they own?
In Homes DetailView I am able to show Owners. I would like to do the same for Homes' DetailView and Homes ListView.

I don't really get it what you asking for,
but if I understand your question correctly,
I assume you want to add Homes list (not HomesOwners list) into your Owners form, right?
you can add extra field in your form like this:
class OwnersForm(ModelForm):
# notice the queryset is 'Homes' not 'HomesOwners'
homes = forms.ModelMultipleChoiceField(queryset=Homes.objects.all(), widget=forms.CheckboxSelectMultiple)
class Meta:
model = Owners
fields = ('homes', 'your_other_fields',)
# then you can access in init function too if you want
def __init__(self, *args, **kwargs):
super(OwnersForm, self).__init__(*args, **kwargs)
self.fields['homes'].required = False
then, since it using CheckboxSelectMultiple widget, you can iterate it in your html template like this:
{% for key, value in your_form.homes.field.choices %} <!-- notice '.field.'-->
{{ key }} = {{ value }}
{% endfor %}
you probably need to create custom save too for your form.
for your question 3, it is not about the form?
If you want to show HomesOwners, you are already doing right.
{% for owner in homes.homesowners_set.all %}
{{ owner.id_owner.id }}
{% endfor %}
but it will work if that homes is only 1 object.
if homes is a queryset, you have to iterate it first
{% for home in homes %}
{% for owner in home.homesowners_set.all %}
{{ owner.id_owner.id }}
{% endfor %}
{% endfor %}
sorry if I misunderstanding your questions,
maybe you can provide your views.py too, so I or others can help you more specific

Return the first image from the model using the tag '{{value | first}}'

I have a list of photos from which I would like to always be the first to add as a profile photo. I found the following '|first' tag in the django documentation, but I have problems to add it in my situation, every time I try to do it in this way, '{{ image_list|first.photo.url }}' i receives nothing.
Any help will be appreciated.
My models.py
class Image(models.Model):
photo = models.ImageField()
added_at = models.DateTimeField(auto_now_add=True)
masseurs = models.ForeignKey(Masseurs, on_delete=models.CASCADE)
views.py
masseur = get_object_or_404(Masseurs, pk=masseurs_id)
image_list = Image.objects.filter(masseurs_id = masseurs_id)
return render(request, 'masseur/masseur_detail.html', {'image_list':image_list})

Since image_list is a QuerySet and not a list, |first won't work. You can however use:
{{ image_list.first.photo.url }}
For reference, see : Accessing Method Calls
Most method calls attached to objects are also available from within templates. This means that templates have access to much more than just class attributes (like field names) and variables passed in from views.

Why don't you do it in the view?
image = Image.objects.filter(masseurs_id=masseurs_id).first()
But if you need to do it in the template:
{{ image_list.first.photo.url }}
This is because image_list is a queryset, so you can get the first item of the queryset with the .first() syntax

how to filter users who are not being followed in django

Friends, I am using django-friendship with django 1.9 to implement user follows. But on a 'users to follow' page, I want to filter those users who aren't being followed by the current user. How should I implement this?
Here is my views.py
def users_to_follow(request):
follow = Follow.objects.following(request.user)
all_users = User.objects.all().exclude(follow)
return render(request,"auths/users_to_follow.html",locals())
and here is my users_to_follow.html
{% for u in all_users %}
{{ u.username }}
Follow
{% endfor %}
I think there is something wrong with views.py . But i haven't been able to figure it out. Help me friends.

The follow name (variable) is a list of user objects. You can get the IDs of those users like these:
follow = Follow.objects.following(request.user)
follow_ids = [x.id for x in follow]
And then use exclude like this:
to_follow = User.objects.all().exclude(id__in=follow)
The to_follow list should contain the users you want.

exclude does not work this way. You can try the following:
def users_to_follow(request):
all_users = User.objects.exclude(following__follower=request.user)
return render(request,"auths/users_to_follow.html",locals())

According to Django QuerySet documentation (emphasis mine):
Field lookups are how you specify the meat of an SQL WHERE clause. They’re specified as keyword arguments to the QuerySet methods filter(), exclude() and get().
So, your exclude() method call can be adjusted as
all_users = User.objects.all().exclude(pk=follow)
And that's it!

Django admin - inline inlines (or, three model editing at once)

I've got a set of models that look like this:
class Page(models.Model):
title = models.CharField(max_length=255)
class LinkSection(models.Model):
page = models.ForeignKey(Page)
title = models.CharField(max_length=255)
class Link(models.Model):
linksection = models.ForeignKey(LinkSection)
text = models.CharField(max_length=255)
url = models.URLField()
and an admin.py that looks like this:
class LinkInline(admin.TabularInline):
model = Link
class LinkSectionInline(admin.TabularInline):
model = LinkSection
inlines = [ LinkInline, ]
class PageAdmin(admin.ModelAdmin):
inlines = [ LinkSectionInline, ]
My goal is to get an admin interface that lets me edit everything on one page. The end result of this model structure is that things are generated into a view+template that looks more or less like:
<h1>{{page.title}}</h1>
{% for ls in page.linksection_set.objects.all %}
<div>
<h2>{{ls.title}}</h2>
<ul>
{% for l in ls.link_set.objects.all %}
<li>{{l.title}}</li>
{% endfor %}
</ul>
</div>
{% endfor %}
I know that the inline-in-an-inline trick fails in the Django admin, as I expected. Does anyone know of a way to allow this kind of three level model editing? Thanks in advance.

You need to create a custom form and template for the LinkSectionInline.
Something like this should work for the form:
LinkFormset = forms.modelformset_factory(Link)
class LinkSectionForm(forms.ModelForm):
def __init__(self, **kwargs):
super(LinkSectionForm, self).__init__(**kwargs)
self.link_formset = LinkFormset(instance=self.instance,
data=self.data or None,
prefix=self.prefix)
def is_valid(self):
return (super(LinkSectionForm, self).is_valid() and
self.link_formset.is_valid())
def save(self, commit=True):
# Supporting commit=False is another can of worms. No use dealing
# it before it's needed. (YAGNI)
assert commit == True
res = super(LinkSectionForm, self).save(commit=commit)
self.link_formset.save()
return res
(That just came off the top of my head and isn't tested, but it should get you going in the right direction.)
Your template just needs to render the form and form.link_formset appropriately.

Django-nested-inlines is built for just this. Usage is simple.
from django.contrib import admin
from nested_inlines.admin import NestedModelAdmin, NestedStackedInline, NestedTabularInline
from models import A, B, C
class MyNestedInline(NestedTabularInline):
model = C
class MyInline(NestedStackedInline):
model = B
inlines = [MyNestedInline,]
class MyAdmin(NestedModelAdmin):
pass
admin.site.register(A, MyAdmin)

My recommendation would actually be to change your model. Why not have a ForeignKey in Link to LinkSection? Or, if it's not OneToMany, perhaps a ManyToMany field? The admin interface will generate that for free. Of course, I don't recommend this if links don't logically have anything to do with link sections, but maybe they do? If they don't, please explain what the intended organization is. (For example, is 3 links per section fixed or arbitrary?)

You can create a new class, similar to TabularInline or StackedInline, that is able to use inline fields itself.
Alternatively, you can create new admin templates, specifically for your model. But that of course overrules the nifty features of the admin interface.