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Django model with multiple foreign keys

I want to create a list of products that are categorized by area, need, and product category. I created 3 separate models that reply on each other so users will easily add categories and select from the dropdown list area and need.
For now, I have 3 areas and under each area I have needs. What I want is to render a list of items from Area model, under each item from Area model all items from Need model and under each item from Need model all items from Product model (only titles).
ProductCategory model is not used here but I need it somewhere else and it is a connector between products and areas/needs. It is much easier to define categories and just select them from the dropdown list when adding a new product.
I need to create a loop that will show me something like above. I know it will not work but I wanted to show the logic.
My question is what is the best approach to render something like this?
How can I get category_area and category_need in my class and in my html?
models.py
class Area(models.Model):
title = models.CharField(max_length=75, blank=False)
body = models.CharField(max_length=150, default='-', blank=False)
publish = models.DateTimeField('publish', default=timezone.now)
class Need(models.Model):
title = models.CharField(max_length=75, blank=False, null=False, help_text='max 75 characters')
body = models.CharField(max_length=150, default='-', blank=False)
publish = models.DateTimeField(default=timezone.now)
need_area = models.ForeignKey(Area, on_delete=models.CASCADE, related_name='need_area')
class ProductCategory(models.Model):
title = models.CharField(max_length=400, blank=False, null=False, help_text='max 400 characters')
body = models.TextField(default='-')
publish = models.DateTimeField('publish', default=timezone.now)
category_area = models.ForeignKey(Area, on_delete=models.CASCADE, related_name='category_area', null=True)
category_need = models.ForeignKey(Need, on_delete=models.CASCADE, related_name='category_need', null=True)
class Product(models.Model):
id = models.AutoField(primary_key=True)
title = models.CharField(max_length=400, blank=False)
category = models.ForeignKey(ProductCategory, on_delete = models.CASCADE, blank=True, related_name='products')
def get_absolute_url(self):
return reverse("product", kwargs={'slug': self.slug})
views.py
class SearchProducts(LoginRequiredMixin, ListView):
login_url = 'login'
redirect_field_name = 'login'
template_name = 'hubble/search/manual_search.html'
model = Product
queryset = Product.objects.all()
def get_context_data(self, **kwargs):
context = super(SearchProducts, self).get_context_data(**kwargs)
product_results = ProductCategory.objects.prefetch_related("products").all()
context['product_results'] = product_results
return context
product_search.html
<div>
{% for area in product_results %}
<h6>{{area.title}}</h6>
{% endfor %}
</div>

You can prefetch_related all backwards relationship and make an iteration similar to this:
areas = Area.objects.prefetch_related('need_area__category_need__products')
for area in areas:
# iterate through each instance of Area
for need in area.need_area.all():
# iterate through each instance of Need for the given area
for product_category in need.category_need.all():
# iterate through each instance of ProductCategory for the given need
for product in product_category.products.all():
# iterate through each instance of product for the given product category

Show list of related objects in a template Django

I have an issue with displaying list of related articles in my Q&A DetailView.
I have a field where user can connect an article to Q&A from admin site. What I want is to display these related articles.
models.py
class QA(models.Model):
id = models.AutoField(primary_key=True)
author = models.ForeignKey(settings.AUTH_USER_MODEL, blank=True, null=True, on_delete=models.SET_NULL) #settings INSTALLED_APPS
title = models.CharField(max_length=750)
category = models.ForeignKey(Category, on_delete = models.CASCADE, blank=True)
related_articles = models.ManyToManyField(Article, default=None, blank=True, related_name='related_article')
slug = models.SlugField(unique=True, blank=True)
class Article(models.Model):
id = models.AutoField(primary_key=True)
author = models.ForeignKey(settings.AUTH_USER_MODEL, blank=True, null=True, on_delete=models.SET_NULL) #settings INSTALLED_APPS
title = models.CharField(max_length=200)
category = models.ForeignKey(Category, on_delete = models.CASCADE, blank=True)
slug = models.SlugField(unique=True, blank=True)
views.py
class QADetailView(LoginRequiredMixin, DetailView):
login_url = 'login'
redirect_field_name = 'login'
template_name = 'QADetailView.html'
model = QA
def get_context_data(self, **kwargs):
categories = Category.objects.all()
related_articles = Article.objects.filter(related_article=self.kwargs['id']) #No idea what to put in filter
#related_articles = Article.objects.filter(related_article='1')
context['related_article'] = related_articles
context['categories'] = categories
return context
QADetailView.html
{% for article in related_article %}
{{article.title}}
{% endfor %}

You don' t need to inject the related articles in the template context, you can simply write in your QADetailView.html template (without any necessary edit):
{% for article in object.related_articles.all %}
{{article.title}}
{% endfor %}

Check RedWheelBorrow's solution first. If that does not work. Try the following:
There might be a better way of structuring your classes. So in Django, it is possible to simulate a hierarchy. For instance, when creating an invoice representation it would look something like this.
from django.db import models
class Invoice(models.Model):
"""Representing a invoice"""
user = models.ForeignKey(to=User, on_delete=models.PROTECT, related_name="invoices", default=1)
title = models.CharField(max_length=200)
date = models.DateField()
start_time = models.TimeField(default=time(9))
duration = models.IntegerField(default=1)
invoice_number = models.CharField(max_length=500, default=increment_invoice_number) # increment_invoice_number this a function that I will leave out of this answer
class InvoiceLine(models.Model):
"""Representing invoice lines of an invoice"""
invoice = models.ForeignKey(to=Invoice, on_delete=models.CASCADE, related_name="lines")
description = models.CharField(_("Beschrijving"), max_length=512)
quantity = models.IntegerField(_("Aantal"), blank=True, default=1)
discount = models.IntegerField(_("Korting in %"), default=0)
Please note, the invoice representation as presented here lacks some attributes to be a fully functional class in production. It still needs tax references, etc. However, it holds the solution to your problem.
The Invoice class has an attribute user that holds a ForeignKey with 'invoices' being its related name. This means it the object must be linked to a User object.
A User can have multiple Invoices. An Invoice can only be linked to one User.
It is one-to-many relationship:
User -> List[Invoice,...]
When looking at the class InvoiceLine we see a similar pattern. The attribute invoice is a ForeignKey with a link to the Invoice class and holds 'lines' as related name. This is also an one-to-many relationship.
Invoice -> List[InvoiceLine, ...]
To obtain the linked objects we can use the following code:
# obtain user
user = User.objects.get(id=<USER_ID>)
# obtain all Invoice objects linked to user
invoices = user.invoices.all()
# print all string representations of Invoice objects
print(invoices)
# obtain all InvoiceLine objects linked to invoices
for invoice in invoices:
lines = invoice.lines.all()
print(lines)
In the above example the highest object is User. A User can hold multiple Invoice objects. A Invoice object can hold multiple InvoiceLine objects. We can use the same strategy to solve your problem.
We want the following representation:
User -> List[QA, ...]
QA -> List[Article, ...]
class QA(models.Model):
id = models.AutoField(primary_key=True)
# So in your case the author is the user.
# Here you define User -> List[QA, ...]
author = models.ForeignKey(settings.AUTH_USER_MODEL, blank=True, null=True, on_delete=models.SET_NULL) #settings INSTALLED_APPS
title = models.CharField(max_length=750)
category = models.ForeignKey(Category, on_delete = models.CASCADE, blank=True)
slug = models.SlugField(unique=True, blank=True)
# related_articles is removed.
class Article(models.Model):
id = models.AutoField(primary_key=True)
author = models.ForeignKey(settings.AUTH_USER_MODEL, blank=True, null=True, on_delete=models.SET_NULL) #settings INSTALLED_APPS
title = models.CharField(max_length=200)
category = models.ForeignKey(Category, on_delete = models.CASCADE, blank=True)
slug = models.SlugField(unique=True, blank=True)**
related_articles = models.ForeignKey(to=QA, on_delete=models.CASCADE, related_name="related_articles")
class QADetailView(LoginRequiredMixin, DetailView):
login_url = 'login'
redirect_field_name = 'login'
template_name = 'QADetailView.html'
model = QA
def get_context_data(self, **kwargs):
categories = Category.objects.all()
# obtain specific QA
qa = QA.objects.get(pk=id, author=self.request.user)) # check how you named the id variable in your url.
# obtain related articles
related_articles = qa.related_articles.all()
# Save in context for use in template.
context['related_articles'] = related_articles # Added an character 's' to key value for there is can be more than one related article.
context['categories'] = categories
return context
{% for article in related_articles %} # Also add character 's' here
{{article.title}}
{% endfor %}
This should do the trick. There might be some improvements on error handling though
I hope this works. If not, let me know.

What is the best way to handle different but similar models hierarchy in Django?

What is the deal: I'm crating a site where different types of objects will be evaluated, like restaurants, beautysalons, car services (and much more).
At the beginning I start with one app with with Polymorfic Model:
models.py:
from django.db import models
from users.models import ProfileUser
from django.utils import timezone
from polymorphic.models import PolymorphicModel
class Object(PolymorphicModel):
author = models.ForeignKey(ProfileUser, on_delete=models.CASCADE)
title = models.CharField(max_length=300)
city = models.ForeignKey(City, on_delete=models.CASCADE)
address = models.CharField(max_length=300)
phone = models.CharField(max_length=20, default='')
email = models.CharField(max_length=100, default='')
site = models.CharField(max_length=100, default='')
facebook = models.CharField(max_length=100, default='')
instagram = models.CharField(max_length=100, default='')
content = models.TextField()
rating = models.DecimalField(default=10.0, max_digits=5, decimal_places=2)
created_date = models.DateTimeField(default=timezone.now)
approved_object = models.BooleanField(default=False)
admin_seen = models.BooleanField(default=False)
def __str__(self):
return f"{self.title}"
class Restaurant(Object):
seats = models.IntegerField()
bulgarian_kitchen = models.BooleanField(default=False)
italian_kitchen = models.BooleanField(default=False)
french_kitchen = models.BooleanField(default=False)
sea_food = models.BooleanField(default=False)
is_cash = models.BooleanField(default=False)
is_bank_card = models.BooleanField(default=False)
is_wi_fi = models.BooleanField(default=False)
category_en_name = models.CharField(max_length=100, default='restaurants')
category_bg_name = models.CharField(max_length=100, default='Ресторанти')
bg_name = models.CharField(max_length=100, default='Ресторант')
is_garden = models.BooleanField(default=False)
is_playground = models.BooleanField(default=False)
class SportFitness(Object):
is_fitness_trainer = models.BooleanField(default=False)
category_en_name = models.CharField(max_length=100, default='sportfitness')
category_bg_name = models.CharField(max_length=100, default='Спорт и фитнес')
bg_name = models.CharField(max_length=100, default='Спорт и фитнес')
class CarService(Object):
is_parts_clients = models.BooleanField(default=False)
category_en_name = models.CharField(max_length=100, default='carservice')
category_bg_name = models.CharField(max_length=100, default='Автосервизи')
bg_name = models.CharField(max_length=100, default='Автосервиз')
class Comment(models.Model):
object = models.ForeignKey(Object, on_delete=models.CASCADE, related_name='comments')
author = models.ForeignKey(ProfileUser, on_delete=models.CASCADE)
content = models.TextField()
rating = models.TextField()
approved_object = models.BooleanField(default=False)
admin_seen = models.BooleanField(default=False)
created_date = models.DateTimeField(default=timezone.now)
def __str__(self):
return f"{self.content}"
class Images(models.Model):
object = models.ForeignKey(Object, default=None, on_delete=models.CASCADE)
image = models.ImageField(upload_to='attachments',
verbose_name='Image')
class ObjectCoordinates(models.Model):
object = models.ForeignKey(Object, on_delete=models.CASCADE, related_name='coordinates')
latitude = models.CharField(max_length=60)
longitude = models.CharField(max_length=60)
Don't mention that name Object is wrong, I already know that :)
So all logic about different objects was in one App and this start to cause some problems, like:
views.py:
def show_object(request, category, pk, page_num):
categories = {'restaurants' : 'Restaurant', 'sportfitness' : 'SportFitness', 'carservice' : 'CarService'} # probably this is not good way to do it
obj = apps.get_model('objects', categories[category]).objects.get(id=pk)
def show_all_objects(request, category, page_num, city=None):
params_map = {
'restaurants': Restaurant,
'sportfitness': SportFitness,
'carservice': CarService,
}
objects = Object.objects.instance_of(params_map.get(category))
and other problems in templates (a lot of if-else blocks) etc.
So I decide to change whole structure and put every model in different app, so now I have app:restaurants, app:sportfitness, app:carservices, etc. But it begin to cause some problems, again, like this model:
class ObjectCoordinates(models.Model):
object = models.ForeignKey(Object, on_delete=models.CASCADE, related_name='coordinates')
latitude = models.CharField(max_length=60)
longitude = models.CharField(max_length=60)
All of objects (restaurants, car services) has coordinates of map, so I'm not sure how to handle it, with Model ObjectCoordinates . If I create ObjectCoordinates for each of them, respectively a table in BD (then I will have some tables with different names but same structure, which is not very good, because except ObjectCoordinates, models share and other common models like Images and others, so at the end I will have a lot of tables with different names and same structure). Probably I should add one more column for object category, if I got two rows with same id of objects?
Probably change ObjectCoordinates and other common models to ManyToMany relation will prevent identical tables, but I'm not quite sure about that. Other problem is that there is a lot of repeated code (in views, templates). Also, now, I don't know how to get all objects (restaurants, car services) when they do not have common point, like Object model in first scenario with Polymorphic Model. Or I should keep different apps but to create common Model for all objects, and all of them to to inherit it.
Questions:
What structure is better, first one or second one?
What is the best wayt to implement such site (model structure)?
Should I create common point (model) for all models who they will inherit?
Here is my third attempt (notice that Object is renamed to Venue):
from django.db import models
from users.models import ProfileUser
from django.utils import timezone
from polymorphic.models import PolymorphicModel
# Create your models here.
class City(models.Model):
name = models.CharField(max_length=20)
def __str__(self):
return f"{self.name}"
class Category(models.Model):
name = models.CharField(max_length=20)
bg_name = models.CharField(max_length=20, default=None)
category_bg_name = models.CharField(max_length=100, default=None)
def __str__(self):
return f"{self.name}"
class Venue(models.Model):
author = models.ForeignKey(ProfileUser, on_delete=models.CASCADE)
title = models.CharField(max_length=300)
city = models.ForeignKey(City, on_delete=models.CASCADE)
address = models.CharField(max_length=300)
phone = models.CharField(max_length=20, default='')
email = models.CharField(max_length=100, default='')
site = models.CharField(max_length=100, default='')
facebook = models.CharField(max_length=100, default='')
instagram = models.CharField(max_length=100, default='')
content = models.TextField()
rating = models.DecimalField(default=10.0, max_digits=5, decimal_places=2)
created_date = models.DateTimeField(default=timezone.now)
approved_venue = models.BooleanField(default=False)
admin_seen = models.BooleanField(default=False)
venue_category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='category')
def __str__(self):
return f"{self.title}"
class VenueFeatures:
seats = models.IntegerField()
bulgarian_kitchen = models.BooleanField(default=False)
italian_kitchen = models.BooleanField(default=False)
french_kitchen = models.BooleanField(default=False)
sea_food = models.BooleanField(default=False)
is_cash = models.BooleanField(default=False)
is_bank_card = models.BooleanField(default=False)
is_wi_fi = models.BooleanField(default=False)
is_garden = models.BooleanField(default=False)
is_playground = models.BooleanField(default=False)
is_fitness_trainer = models.BooleanField(default=False)
is_parts_clients = models.BooleanField(default=False)
is_hair_salon = models.BooleanField(default=False)
is_laser_epilation = models.BooleanField(default=False)
is_pizza = models.BooleanField(default=False)
is_duner = models.BooleanField(default=False)
is_seats = models.BooleanField(default=False)
is_external_cleaning = models.BooleanField(default=False)
is_internal_cleaning = models.BooleanField(default=False)
is_engine_cleaning = models.BooleanField(default=False)
is_working_weekend = models.BooleanField(default=False)
is_kids_suitable = models.BooleanField(default=False)
is_working_weekend = models.BooleanField(default=False)
venue = models.ForeignKey(Venue, on_delete=models.CASCADE, related_name='venue')
class Comment(models.Model):
venue = models.ForeignKey(Venue, on_delete=models.CASCADE, related_name='comments')
author = models.ForeignKey(ProfileUser, on_delete=models.CASCADE)
content = models.TextField()
rating = models.TextField()
approved_venue = models.BooleanField(default=False)
admin_seen = models.BooleanField(default=False)
created_date = models.DateTimeField(default=timezone.now)
def __str__(self):
return f"{self.content}"
class Images(models.Model):
venue = models.ForeignKey(Venue, default=None, on_delete=models.CASCADE)
image = models.ImageField(upload_to='attachments',
verbose_name='Image')
class VenueCoordinates(models.Model):
venue = models.ForeignKey(Venue, on_delete=models.CASCADE, related_name='coordinates')
latitude = models.CharField(max_length=60)
longitude = models.CharField(max_length=60)
Now I do not now how to use Venue with VenueFeatures
Notice that features are just true/false values (checkboxes in form).

Okay, this is probably the best way to abstract anything as much as I can:
from django.db import models
from users.models import ProfileUser
from django.utils import timezone
from polymorphic.models import PolymorphicModel
# Create your models here.
class City(models.Model):
name = models.CharField(max_length=20)
def __str__(self):
return f"{self.name}"
class Category(models.Model):
name = models.CharField(max_length=20)
bg_name = models.CharField(max_length=20, default=None)
category_bg_name = models.CharField(max_length=100, default=None)
icon = models.CharField(max_length=40, default=None)
def __str__(self):
return f"{self.name}"
class Venue(models.Model):
author = models.ForeignKey(ProfileUser, on_delete=models.CASCADE)
title = models.CharField(max_length=300)
city = models.ForeignKey(City, on_delete=models.CASCADE)
address = models.CharField(max_length=300)
phone = models.CharField(max_length=20, default='')
email = models.CharField(max_length=100, default='')
site = models.CharField(max_length=100, default='')
facebook = models.CharField(max_length=100, default='')
instagram = models.CharField(max_length=100, default='')
content = models.TextField()
rating = models.DecimalField(default=10.0, max_digits=5, decimal_places=2)
created_date = models.DateTimeField(default=timezone.now)
approved_venue = models.BooleanField(default=False)
admin_seen = models.BooleanField(default=False)
category = models.ForeignKey(Category, on_delete=models.CASCADE)
def __str__(self):
return f"{self.title}"
class Feature(models.Model):
name = models.CharField(max_length=100)
code = models.CharField(max_length=100 )
category = models.ForeignKey(Category, on_delete=models.CASCADE)
type = models.CharField(max_length=100)
def __str__(self):
return f"{self.name}"
class VenueFeatures(models.Model): # ManyToMany Venues <-> Features
venue = models.ForeignKey(Venue, on_delete=models.CASCADE)
feature = models.ForeignKey(Feature, on_delete=models.CASCADE)
value = models.CharField(max_length=255)
class Comment(models.Model):
venue = models.ForeignKey(Venue, on_delete=models.CASCADE, related_name='comments')
author = models.ForeignKey(ProfileUser, on_delete=models.CASCADE)
content = models.TextField()
rating = models.TextField()
approved_venue = models.BooleanField(default=False)
admin_seen = models.BooleanField(default=False)
created_date = models.DateTimeField(default=timezone.now)
def __str__(self):
return f"{self.content}"
class Images(models.Model):
venue = models.ForeignKey(Venue, default=None, on_delete=models.CASCADE)
image = models.ImageField(upload_to='attachments',
verbose_name='Image')
class VenueCoordinates(models.Model):
venue = models.ForeignKey(Venue, on_delete=models.CASCADE, related_name='coordinates')
latitude = models.CharField(max_length=60)
longitude = models.CharField(max_length=60)
Now Features are bound with Categories
Also Venues are ManyToMany with Features
I have already linked it to business logic and it works fine.

TL;DR Use a JSONField (JSONB automatically I think) in PostgreSQL WITHOUT a GIN index for your VenueFeatures instead of creating an entirely new model. Postgres has come a long way towards NoSQL/unstructured DB and it's really good. Using a JSONField in your Venue model would work really well. At the very bottom, I talk about how I would design your site's db.
Although I hate saying this, but this could be the job of a NoSQL database. Usually every application uses RDBM which is structured, but you are using unstructured attributes. You could try using PostgreSQL's JSONB field but... stuffing everything into one field would be tiresome for the GIN index + caching.
For now, I'll ignore a lot of weird practices such as needing to partition a couple of attributes, max_length for char field is typically 255 length for all databases, making sure the most accessed tables don't have too many attributes so that caching is better (i.e. you don't have to invalidate your cache every time a user updates your table), GeoDjango for your coordinate system with the standard Mercator projection system on Postgres Geography mode, and you could use sets instead of dicts (sets are iterables and use {} but nothing is repeated)...
Stay away from this option: For one, I NEVER recommend MongoDB, but it could be useful for you... so long as your application doesn't grow too large as in a couple million records could break your system.
The other RECOMMENDED option is PostgreSQL's JSONB or Django's JSONField withOUT a GIN index (I strongly recommend you don't index this field since venues could change them sooo often to the point that REINDEXING and caching would burn your server and slow your app). It can be useful to store a venue's "Features" inside of this JSONB field since everything is super unstructured.
Lowering the number of attributes is better. You've got A LOT of them too which could slow down querying. I recommend you use Django-cachalot for caching since they support JSONField which can avoid your issue of having a LOT of attributes.
Other recommendations in general
Instead of using default='', just do blank=True, null=True since you're basically saying the user doesn't have to fill out the email field.
Kind of like how you would have a user profile instead of stuffing ALL of your attributes inside of the main User model, you want to partition your Venue data into different models.
The way I would've designed this:
Since you originally had these three venues, just make the "Categories" table into choices.
from django.contrib.gis.db import models # This also imports standard models
from django.contrib.postgres.fields import JSONField # Remember to turn on GeoDjango with PostgreSQL's PostGIS extension
from django.contrib.postgres.indexes import BrinIndex
class Venue(models.Model):
id = models.BigAutoField(primary_key=True)
title = models.CharField(max_length=255)
rating = models.DecimalField(default=10.0, max_digits=5, decimal_places=2)
created_date = models.DateTimeField(default=timezone.now)
approved_venue = models.BooleanField(default=False)
admin_seen = models.BooleanField(default=False)
VENUE_TYPES = [
(1, "restaurant"),
(2, "concert"),
(3, "art night")
]
category = SmallPositiveIntegerField(choices=VENUE_TYPES)
location = models.PointField(srid=4326) # mercator projection from GeoDjango. You don't have to use this; you can stick to your old city and address thing
class Meta:
indexes = (
BrinIndex(fields=['category']), # this is in case you have a LOT of categories later on.
)
class VenueProfile(models.Model):
venue = models.OneToOneField(Venue, on_delete=models.CASCADE, primary_key=True)
misc_features = JSONField() # This field is for stuff like your restaurant features OR your concert features. You can put whatever you want in there. Just make sure you have a list of features that people have when trying to access the JSON so you don't run into exceptions.
created_date = models.DateTimeField(auto_now_add=True)
facebook = models.CharField(max_length=100, blank=True, null=True)
instagram = models.CharField(max_length=100, blank=True, null=True)
city = models.ForeignKey(City, on_delete=models.SET_NULL, null=True) # SET_NULL in case you accidentally delete a city. You don't want to also delete the venue.
image = models.ImageField(upload_to='attachments',
verbose_name='Image')
# These attributes are universal for ANY venue so that's why they don't need to be in the JSONField
"""
For the rest of the features, I have no concern EXCEPT for city. Because you're using GeoDjango, you should also use MaxMind's free city database to determine location based on coordinates. That way, you've essentially scraped the need to store the user and such. You could probably save the address field since it could make things easier that a simple coordinate. It's really up to you. You could also use both!
"""
The attributes I've added to the Venue model are THE MOST important things in my opinion that a user would immediately want to know about.
The VenueFeature model is something that isn't updated that much. It's PRIME for using Django-cachalot to take over since it's not modified that often. (50 modifications per second makes invalidation of caches per modification a big hassle).
Comments model is fine.

Make model field equal concatenation of two fields in Django

I have two models and want to create a field for the second class that is a concatenation of a foreign field and a field within the model.
The code I have so far is:
class Drug(models.Model):
drug_name = models.CharField("Drug Name", max_length=200)
reference_title = models.CharField("Publication Title",max_length=1024)
pub_date = models.DateField("Pubication Date",'date published')
pubmed_link = models.CharField("PubMed Link", max_length=300)
class Risk(models.Model):
drug_link = models.ForeignKey(Drug, on_delete=models.CASCADE)
dosage = models.IntegerField(default=0)
independent_risk = models.DecimalField("Individual Risk", max_digits=4, decimal_places=2)
I want to add a new field to the Risk model that is automatically populated by a concatenation of the selected value for drug_link and the entered value for dosage.

This can be accomplished by a python property on the class:
class Risk(models.Model):
drug_link = models.ForeignKey(Drug, on_delete=models.CASCADE)
dosage = models.IntegerField(default=0)
independent_risk = models.DecimalField("Individual Risk", max_digits=4, decimal_places=2)
#property
def name_dosage(self):
return "%s - %s" % ( self.drug_link.drug_name, self.dosage )

If you do not need to store this value in database but rather use it in templates, you would not need to create extra fields. You can use methods like this:
class Risk(models.Model):
drug_link = models.ForeignKey(Drug, on_delete=models.CASCADE)
dosage = models.IntegerField(default=0)
independent_risk = models.DecimalField("Individual Risk", max_digits=4, decimal_places=2)
def dosages(self):
return "{} - {}".format(self.drug_link.drug_name, self.dosage)
And in the templates, you can just do:
{% for risk in risks %}
{{ risk.dosage }}
{% endfor %}

Trouble accessing ForeignKey elements

I currently have two models set up in my Django app that have a ForeignKey relationship.
class Post(models.Model):
title = models.CharField(max_length=100)
body = RichTextField(config_name='awesome_ckeditor')
pub_date = models.DateTimeField('date', null=True)
description = models.CharField(max_length=100, blank=True, null=True)
photo = models.ImageField(upload_to='media/', blank=True, null=True)
def __unicode__(self):
return self.title
class Comment(models.Model):
post = models.ForeignKey(Post, related_name="comments", blank=True, null=True)
name = models.CharField(max_length=100, null=True)
comment = models.TextField(blank=True)
pub_date = models.DateField("date", blank=True, null=True)
def __unicode__(self):
return unicode(self.name)
What I am not getting is making queries between the two. I have tried making queries through the shell but to no success. If I set Post(title="Cat") and then make c = Comment(name="Dog"), I can query each models respective title or name through something like p = Post.object.get(pk=1) and p.title will output Cat. But if I do p.comment or p.comment_id, there is an error. Likewise with any Comment objects. However when I do print c.post, I get None. What am I missing in order to make p.<field_here>" =Dog`?

Since you have related name "comments", access to set foreign model from Post should be called this way:
p.comments
But since you can have many comments for a same Post, this won't return a unique value, but a related manager that you need to query. So you could get:
p.comments.filter(name="Dog")