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.
Related
This is my first time working with Django and while working I have encountered with a confusion to create a particular statement in views that leads to my desired output. I have created a model 'Parents' which has data of a specific student (Foreign Key), and I am confused to access that student id for further process like working with Attendance, or Results of that specific student. Below are necessary codes and my trial to fetch data.
Models.py
class Students(models.Model):
id = models.AutoField(primary_key=True)
admin = models.OneToOneField(CustomUser, on_delete=models.CASCADE)
gender = models.CharField(max_length=50)
address = models.TextField()
course_id = models.ForeignKey(Courses, on_delete=models.DO_NOTHING, default=1)
session_year_id = models.ForeignKey(SessionYearModel, on_delete=models.CASCADE)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
objects = models.Manager()
def __str__(self):
return self.admin.first_name + " " + self.admin.last_name
class Parents(models.Model):
id = models.AutoField(primary_key=True)
admin = models.OneToOneField(CustomUser, on_delete=models.CASCADE)
gender = models.CharField(max_length=50)
**student = models.ForeignKey(Students, on_delete=models.CASCADE)**
relation = models.CharField(max_length=255)
address = models.TextField()
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
objects = models.Manager()
def __str__(self):
return self.admin.first_name + " " + self.admin.last_name
Here I have two models, Students model has all information regarding student and the other model is Parent model which has parent information with its specific student id.
Below is the views file code where I am trying to fetch student id of currently logged in parent,
def HOME(request):
stud_data = Parents.objects.filter(student__id = request.user.id)
print(stud_data)
return None
At the time of page reload, I am able to get an empty QuerySet[] as it is not able to find the id.
Kindly help me finding the solution to this problem, so that I can continue thinking about the development.
Thanks :)
As you mentioned here, you are looking for Student data for currently logged in Parent. Hence you can look for Student data directly from Parent object. Like this:
stud_object = request.user.parent.student
This relation works because Parent has a OneToOne relation with CustomUser (I assume Authentication's custom User model), hence you should get Parent object from request.user.parent (reverse relation for OneToOne). Also, student field is a ForeignKey of Parent model.
Addionally, I think the relation between Parent and Student should be ManyToMany, because a Student can have multiple parents and one parent can have multiple students (or children).
There are two possibilities:
The View code that you have attached should be returning stud_data not None, but I am assuming that you know this and this current state of the code is just for debugging purposes.
The request.user.id contains a value that doesn't belong to any student's ID in the database. As you are using filter, it's not going to complain about it and just return you an empty QuerySet. I'd suggest using the get() filter here which raises the DoesNotExist exception and would help in debugging as well.
def home(request):
stud_data = Parents.objects.get(student__id = request.user.id)
return stud_data
Hope it helps!
Best of luck with your new journey!
I'm new to Django so I make 3 simple tables to return a WishList. The thing is that I want whenever user asks for WishList, his/her user_id is used to make a SELECT query to return his/her own WishList. And I want to get product title and product url from my WishList table. I'm using to_field but with that way I only can get product title back. I don't know much about Django so help me!
Product
class Product(models.Model):
class Meta:
unique_together = (('id', 'title'),)
title = models.CharField(max_length=200, unique=True,
help_text='Name of the product')
url = models.CharField(max_length=300, default='',
help_text='Url of the product')
def __str__(self):
return 'Product: {}'.format(self.title)
WishList
class WishList(models.Model):
class Meta:
unique_together = (('user', 'product'),)
user = models.ForeignKey(fbuser,
on_delete=models.CASCADE,
help_text='Facebook user',
to_field='user_id')
product = models.ForeignKey(Product, to_field='title', db_column='title',
on_delete=models.CASCADE)
def __str__(self):
return 'WishList: {}'.format(self.user)
It's not a good practice to override to_field to another field different than your model.pk unless you have a really good reason and you know what you are doing (definitely not the case right now).
So after you read the docs, you will know that in order to get wishlisht related to a user, you can use the ForeignKey reverse relation to get all related wishlists for a user.
user_wishlists = my_user.wishlist_set.all()
#Because we know that you want to access the wishlist.products
#in order to optimize things (in terms of db queries)
#you can add and .select_related('product')
#e.g, user_wishlists = my_user.wishlist_set.all().select_related('product')
#now follow the wishlist.product foreign key to access the related product for every wishlist
for wishlist in user_wishlists:
product = wishlist.product
print (product.id, product.title, product.url)
Now after you read a little bit more of the documentation
you will notice that your WishList model is in fact an intermediate model for a ManyToMany relation between User and his wished products, then you will know that you can define a M2M field between user and products via WishList like so:
class FbUser(models.Model):
#...
wished_products = models.ManyToManyField(
Product,
through='WishList',
through_fields=('user', 'product')
)
#and now accessing user wished products would be easy as:
user_wished_products = my_user.wished_products.all()
for product in user_wished_products:
print (product.id, product.title, product.url)
I'm struggling with django querysets and GROUP BY queries, I know there are plenty of similar questions, but I really don't get it:/
I would like to be able to create a request similar to this one (SQLite):
SELECT MAX(fb_game_score.value), fb_game_fbuser.first_name, fb_game_fbuser.last_name
FROM fb_game_score
JOIN fb_game_game ON (fb_game_score.game_id = fb_game_game.id)
JOIN fb_game_fbuser ON (fb_game_game.user_id = fb_game_fbuser.id)
GROUP BY fb_game_fbuser.fb_user_id;
The query is quite simple, it lists the users scores by showing only the best score for each players.
For clarification here's the model classes:
class FBUser(AbstractUser):
fb_user_id = models.CharField(max_length=100, null=True)
oauth_token = models.CharField(max_length=1024, null=True)
expires = models.IntegerField(null=True)
highest_score = models.IntegerField(null=True)
class Game(models.Model):
identifier = models.CharField(max_length=100, db_index=True)
user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='games')
class Score(models.Model):
game = models.ForeignKey(Game, related_name='scores')
value = models.IntegerField()
date = models.DateTimeField(auto_now=True)
timestamp = models.FloatField(default=0)
inter = models.BooleanField(default=False)
There's no high-level group_by in the queryset. It's used in calls to aggregate and annotate but it is not available to you.
There's a low-level API which is not documented at all. You can get an internal query description:
queryset = ... #whatever query you'd want to group by
query = queryset.query
and then you can alter the group_by member -which is a list- by adding a field which you'd want to group by:
query.group_by.append('a_field')
But:
you have to seriously know what you're doing.
there's no guarantee of stability of this API.
The current alternative for this is falling back to a raw (django.db.connection.* methods) SQL query.
Edit: I just saw this 3rd-party application which could help you with reports. I don't know if you can use in-code reports, or you have to limit yourself to in-view reports (i.e.: don't know if you can process reports in code or just have them as final results).
Hey, I have models like this:
class Galleries(models.Model):
creation_date = models.DateTimeField()
name = models.CharField(max_length=255, unique=True)
gallery_type = models.ForeignKey(Categories)
class Categories(models.Model):
handle = models.CharField(max_length=255, unique=True)
class Values(models.Model):
category = models.ForeignKey(Categories)
language = models.CharField(max_length=7)
category_name = models.CharField(max_length=50)
And now, I just want to reach the values of categories by starting from Galleries. For example: galleries = Galleries.objects.get(id=1). And now I want to reach somehow the values by using this "galleries" object... To get values with specific language would be much more better... I miss skills in Django ORM, so if you can, please point me to some docs or give some code example. Thanks!
galleries = Galleries.objects.get(id=1)
values = galleries.gallery_type.values_set.filter(language='language')
Interestingly, you used the exact wording that the docs use to refer to the related field lookups. I always found the definition strange to the gut, maybe because they put it in quotes.
FOLLOWING RELATIONSHIPS "BACKWARD"
http://docs.djangoproject.com/en/1.2/topics/db/queries/#following-relationships-backward
You may want to use the select_related method of objects so you reduce the number of queries you are making. select_related
gallery = Galleries.objects.select_related().get(id=1)
You can set a related name for the Values model in the category fk:
class Values(models.Model):
category = models.ForeignKey(Categories, related_name="categories")
language = models.CharField(max_length=7)
category_name = models.CharField(max_length=50)
now you can get your list of values for a specific language by doing
values = gallery.gallery_type.categories.filter(language="language")
i have a model that is having multiple many to many relation to another model it is as follows:
class Match(models.Model):
"""Model docstring"""
Match_Id = models.AutoField(primary_key=True)
Team_one = models.ManyToManyField('Team',related_name='Team one',symmetrical=False,)
Team_two = models.ManyToManyField('Team',related_name='Team two',symmetrical=False,)
stadium = models.CharField(max_length=255, blank=True)
Start_time = models.DateTimeField(auto_now_add=False, auto_now=False, blank=True, null=True)
Rafree = models.CharField(max_length=255, blank=True)
Judge = models.CharField(max_length=255, blank=True)
winner = models.ForeignKey('Team', related_name='winner',to_field='Team_Name')
updated = models.DateTimeField('update date', auto_now=True )
created = models.DateTimeField('creation date', auto_now_add=True )
what is the best way to implement model like this ?. all though django does not throw any errors when passing the model sql once syncdb is excuted it throws up errors saying there is no unique constraint matching given keys
Are you sure Team_one and Team_two should be ManyToMany fields? Surely, a match only has a single team on each side - in which case these should both be ForeignKeys.
Using spaces in related_name attribute makes me uneasy, but I think the real problem is connected to the use of to_field attribute on the winner field. As far as I know you can set database relations only to unique fields. It doesn't really make sense to relate to another object using a field that may not be unique.
I'm not sure what do you want to achieve by connecting through this particular field. You usually connect models using primary key fields. This still allows you to access any other field on the related object.