Develop Reference

How to get list of all objects associated with a foreign key in Django

Not super experienced with Django so I apologize if this is trivial. Say I had a category instance and I wanted to get access to all of the content objects that I have previously added to my foreign key. How would I do so?
class Organization(models.Model):
id = models.CharField(primary_key=True, max_length=200, default=uuid4, editable=False, unique=True)
name=models.CharField(max_length=200,unique=True)
phoneNumber=models.CharField(max_length=20)
logo=models.CharField(max_length=100000) # storing this as base 64 encoded
location=models.CharField(max_length=200)
class Category(models.Model):
categoryName=models.CharField(max_length=300, unique=True, primary_key=True)
associatedOrganizations=models.ForeignKey(Organization,on_delete=models.CASCADE,related_name='associatedOrgs',null=True,blank=True)
associatedContent=models.ForeignKey(Content, on_delete=models.CASCADE,related_name='associatedContent',null=True,blank=True)
associatedMeetingNotices=models.ForeignKey(MeetingNotice,on_delete=models.CASCADE,related_name='associatedMeetingNotices',null=True,blank=True)
For example:
say I had the following
healthcareCategory=models.Category.objects.get(pk="healthcare")
and I wanted to access all Organizations related to healthcare, what should I do?
This?
healthcareCategory.associatedOrganizations.all()

You are close. You may want to change that related name from associatedOrgs to be associatedorgs to follow more closely to the django coding style. Documentation on this has a few examples.
healthcare_category = Category.objects.get(pk="healthcare")
organizations = healthcare_category.associatedorgs.all()

The answer by #AMG is correct. If you had not defined a related_name for associatedOrganizations you could simply do
organizations = Organization.objects.filter(category__pk='healthcare')
But I think there is another issue. Am I correct in saying that an Organization can have only one Category, but a Category can have many Organizations?
If so, then I think the ForeignKey in your model is in the wrong place.
class Organization(models.Model):
id = models.CharField(primary_key=True, max_length=200, default=uuid4, editable=False, unique=True)
name=models.CharField(max_length=200,unique=True)
phoneNumber=models.CharField(max_length=20)
logo=models.CharField(max_length=100000) # storing this as base 64 encoded
location=models.CharField(max_length=200)
# The ForeignKey should be here:
category = ForeignKey(Category, on_delete=models.CASCADE)
class Category(models.Model):
categoryName=models.CharField(max_length=300, unique=True, primary_key=True)
# remove this
# associatedOrganizations=models.ForeignKey(Organization,on_delete=models.CASCADE,related_name='associatedOrgs',null=True,blank=True)
...
The ForeignKey is a ManyToOneField so you place it in the model that will be the many, and you link it to the model that will be the one.
Now you can find all organizations within the healthcare category like this:
organizations = Organization.objects.filter(category='healthcare')

Error inserting data into Django database field with a OneToOnefield

I've asked this question before and tried to Google it but I've had no luck, so I have simplified my question. I have two very simple models: one holds some shift numbers and the other holds some data related to the sale of gift cards during a shift. In this case, we have an employee who worked shift "1234" and sold $200.45 and $43.67 worth of gift card from each of two terminals. The models are below:
class Data_Shifts(models.Model):
shift_id = models.CharField(max_length=25, primary_key=True, db_column="shift_id", verbose_name="Shift ID")
def __str__(self):
return str(self.shift_id)
class Data_GiftCards(models.Model):
shift_id = models.OneToOneField('Data_Shifts', on_delete=models.CASCADE, primary_key=True, db_column="shift_id", verbose_name="Shift ID")
net_sales_terminal_1 = models.DecimalField(max_digits=8, decimal_places=2, default=0)
net_sales_terminal_2 = models.DecimalField(max_digits=8, decimal_places=2, default=0)
def __str__(self):
return str(self.shift_id)
I then try to insert some test data into the table using the following command:
Data_GiftCards.objects.create(shift_id="1234", net_sales_terminal_1="200.45", net_sales_terminal_2="43.67")
Upon submitting the web form, I get the following error:
Cannot assign "'1234'": "Data_GiftCards.shift_id" must be a "Data_Shifts" instance.
I am boggled by this. I have a workaround that bypasses django and inserts directly into the table successfully, but this is dirty and I'd prefer to use the proper Pythonic Django way. What am I doing wrong here?
Many thanks in advance.

That is because you name your field shift_id. Django's ORM maps the name of the field in your model to an instance of the related model, not to an ID.
You can still work with IDs instead of instances, but then you have to add _id to the end of your field name.
In your case, you have two options, you can simply do that, which would mean your query should look like:
Data_GiftCards.objects.create(shift_id_id="1234", net_sales_terminal_1=200.45, net_sales_terminal_2=43.67)
But shift_id_id looks redundant, so you can tweak the other end and remove the _id suffix in your model:
class Data_GiftCards(models.Model):
shift = models.OneToOneField('Data_Shifts', on_delete=models.CASCADE, primary_key=True, db_column="shift_id", verbose_name="Shift ID")
net_sales_terminal_1 = models.DecimalField(max_digits=8, decimal_places=2, default=0)
net_sales_terminal_2 = models.DecimalField(max_digits=8, decimal_places=2, default=0)
def __str__(self):
return str(self.shift)
Then you will have to query as you are doing, but you should not use strings if the field types are numeric.
Data_GiftCards.objects.create(shift_id="1234", net_sales_terminal_1=200.45, net_sales_terminal_2=43.67)
Also, you don't need the attribute db_column="shift_id". If your field name is shift, the name of the field in the database table will already be shift_id.

How to access data using reverse foreign key reference in django

I have a model named UserProfile and a model PersonalInformation. I would like to fetch all the data of PersonalInformation using UserProfile model when the user is logged into the webiste but i have a foreign key refernce in the PersonalInformation model with the UserProfile model so how do i fetch the personal information using UserProfile model?
User Profile Model :
class UserProfile(models.Model):
"""Represents a user's model inside our system"""
email = models.EmailField(max_length=255, unique=True)
name = models.CharField(max_length=255)
profile_picture = models.ImageField(upload_to='photos/%y/%m/%d/')
is_active = models.BooleanField(default=True)
is_staff = models.BooleanField(default=False)
highest_degree_earned = models.CharField(max_length=255, blank=False)
college_name = models.CharField(max_length=255, blank=False)
graduation_year = models.IntegerField(default=2020, blank=False)
Personal Information Model :
class PersonalInformation(models.Model):
"""Represents a user's personal Infromation inside our system"""
user = models.ForeignKey(UserProfile, on_delete=models.CASCADE)
mobile = models.CharField(max_length=10 ,blank=True)
bio = models.TextField(max_length=200, blank=True)
college_university = models.CharField(max_length=100, blank=False)
course = models.CharField(max_length=100, blank=False)

First of all, in the code, you are showing you have the names of the models wrong. The UserProfile model name is set as PersonalInformation, change it or the migrations won't work (it's not accepted on the database no matter which one you're using).
Referent to the question you're asking, to fetch the related instance of PersonalInformation of a certain UserProfile instance you should just query the next:
user = UserProfile.objects.get(id='') #Introduce the id of the user you want to fetch its personal information.
user.personalinformation_set.all() # This will return you a QuerySet with all the related instances of PersonalInformation class.
user.personalinformation_set.get(id='') #To get a specific one or you may use a filter to get a filtered QS.
If you want, you can use the related_name attribute for ForeignKey class in order to set a different name from personalinformation_set.
I recommend you too to read the Django documentation, it's really well explained and clear I think:
https://docs.djangoproject.com/en/2.2/topics/db/examples/many_to_one/
As I've seen in a comment, you may also think to use a OneToOne relation instead of ForeignKey if you only expect one instance of PersonalInformation per User. The documentation is at:
https://docs.djangoproject.com/en/2.2/topics/db/examples/one_to_one/

How to filter a one-to-one generic relation with Django?

I have a moderation model :
class ItemModeration(models.Model):
class Meta:
indexes = [
models.Index(fields=['object_id', 'content_type']),
]
unique_together = ('content_type', 'object_id')
content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
object_id = models.PositiveIntegerField()
item = GenericForeignKey('content_type', 'object_id')
published = models.BooleanField(default=False)
...
A descriptor to attach a moderation object on-the-fly :
class ItemModerationDescriptor(object):
def __init__(self, **default_kwargs):
self.default_kwargs = default_kwargs
def __get__(self, instance, owner):
ctype = ContentType.objects.get_for_model(instance.__class__)
try:
moderation = ItemModeration.objects.get(content_type__pk=ctype.id,
object_id=instance.pk)
except ItemModeration.DoesNotExist:
moderation = ItemModeration(item=instance,**self.default_kwargs)
moderation.save()
return moderation
And a model I want to moderate :
class Product(models.Model):
user = models.ForeignKey(
User,
null=True,
on_delete=models.SET_NULL)
created = models.DateTimeField(
auto_now_add=True,
blank=True, null=True,
)
modified = models.DateTimeField(
auto_now=True,
blank=True, null=True,
)
name = models.CharField(
max_length=PRODUCT_NAME_MAX_LENGTH,
blank=True, null=True,
)
moderation = ItemModerationDescriptor()
Now I can see a product 'published' state easily :
p=Product(name='my super product')
p.save()
print(p.moderation.published)
-> False
The generic relation is useful because I will be able to search the objects to moderate whatever the type is : it could be products, images, comments.
to_moderate_qs = ItemModeration.objects.filter(published=False)
Now, how can I get a filtered list of published products ?
I would like to do something like this
published_products_qs = Product.objects.filter(moderation__published=True, name__icontains='sony')
But, of course, it won't work as moderation attribute is not a Django model field.
How can I do that efficiently ? I am thinking a about an appropriate JOIN, but I cannot see how to do that with django without using raw SQL.

Django has a great built in answer for this: the GenericRelation. Instead of your descriptor, just define a generic relation on your Product model and use it as a normal related field:
from django.contrib.contenttypes.fields import GenericRelation
class Product(models.Model):
...
moderation = GenericRelation(ItemModeration)
Then handle creation as you normally would with a related model, and filtering should work exactly as you stipulated. To work as your current system, you'd have to put in a hook or save method to create the related ItemModeration object when creating a new Product, but that's no different from other related django models. If you really want to keep the descriptor class, you can obviously make use of a secondary model field for the GenericRelation.
You can also add related_query_name to allow filtering the ItemModeration objects based only on the Product content type.
WARNING if you do use a GenericRelation note that it has a fixed cascading delete behavior. So if you don't want ItemModeration object to be deleted when you delete the Product, be careful to add a pre_delete hook or equivalent!
Update
I unintentionally ignored the OneToOne aspect of the question because the GenericForeignKey is a one-to-many relation, but similar functionality can be effected via smart use of QuerySets. It's true, you don't have access to product.moderation as a single object. But, for example, the following query iterates over a filtered list of products and extracts their name, the user's username, and the published date of the related ModerationItem:
Product.objects.filter(...).values_list(
'name', 'user__username', 'moderation__published'
)

You'll have to use the content_type to query the table by specific model type.
like this:
product_type = ContentType.objects.get_for_model(Product)
unpublished_products = ItemModeration.objects.filter(content_type__pk=product_type.id, published=False)
For more details on the topic check contenttypes doc

Dynamic generation ForeignKey fields on admin page django

I have models:
class CompanyInfo(models.Model):
name = models.CharField('Имя компании',max_length=250)
class Staff(models.Model):
company_name = models.ForeignKey(CompanyInfo)
date = models.DateField( )
name = models.CharField( max_length=30, )
class Relation(models.Model):
company_name = models.ForeignKey(CompanyInfo)
who = models.ForeignKey(Staff, related_name="who")
with_whom = models.ForeignKey(Staff, related_name="with_whom")
info = models.CharField( max_length=30, )
How I can create dynamic generation fields for WHO and WITH_WHOM form element on the admin-page? I chose COMPANY_NAME, and fields WHO and WITH_WHOM that show only people from that company.

Can you please elaborate in a bit more detail on what you mean by dynamic generation fields? Otherwise, I'm afraid it's a bit difficult to help you because it's not really clear what your problem is.
Besides that, let me tell you that your model design is rather odd, especially your Relation model. If you want to establish a many-to-one relationship between two instances of the same model (I think that's what you are trying to accomplish here), then you should write it like that and get rid of your Relation model:
class Staff(models.Model):
with_whom = models.ForeignKey('self')