I have one problem
Looking below:
I have this model:
class Shoes(models.Model):
shop = models.ForeignKey(Store, related_name="%(class)s")
name = models.ForeignKey(ShoesItem)
size = models.ManyToManyField(ShoesSize, help_text=_("Get useful sizes"))
price = models.IntegerField()
in my case, I have models ShoesSize for store all ShoesSize and ShoesItem for store this Item
How can I get all sizes and all shops from ShoesItem instance?
there are (not full, for example):
class Store(models.Model):
name = models.CharField(max_length=255)
class Item(models.Model):
name = models.CharField(max_length=255)
brand = models.ForeignKey(Brand, related_name="%(app_label)s_%(class)s")
sysname = models.SlugField(max_length=255)
has_shop = models.BooleanField(editable=False, default=False)
description = models.TextField(blank=True, verbose_name="Описание")
color = models.ManyToManyField(Color, blank=True, related_name='%(app_label)s_%(class)s')
and I get list of instances of Item models. After that, I want to get all available sizes and shops for all kind of items
Use a reverse query by using the model name.
Get a ShoesItem:
shoes_item = ShoesItem.objects.all()[0]
Get ShoesSize objects for the ShoesItem via Shoes object:
sizes = ShoesSize.objects.filter(shoes__name=shoes_item)
Get Store objects for the ShoesItem via Shoes object:
shops = Store.objects.filter(shoes__name=shoes_item)
See more - Lookups that span relationships
For a queryset of ShoesItem:
shoes_items = ShoesItem.objects.filter(has_shop=True)
sizes = ShoesSize.objects.filter(shoes__name__in=shoes_items)
shops = Store.objects.filter(shoes__name__in=shoes_items)
Related
I'm working on a Django Rest project where I'm given two MySQL tables:
metrics: Contain a row for each potential metric
daily_data: Contains a row for each data entry where the column names refer to metrics from the 'metrics' table
What I want to do now, is creating new entries in 'metrics' which should be automatically added to existing 'daily_data' entries (with a default value) and displayed on the website.
Here is how the current models looks like:
class Metrics(model.Model):
metric_id = models.CharField(max_length=255, primary_key=True)
is_main_metric = models.BooleanField(default=False)
name = models.CharField(max_length=255, blank=False, null=False)
description = models.CharField(max_length=255, blank=False, null=False)
lower_bound = models.FloatField(default=0.0, null=False)
upper_bound = models.FloatField(default=0.0, null=False)
class Meta:
verbose_name_plural = "Metrics"
db_table = "metrics"
class DailyData(models.Model):
location = models.CharField(max_length=255, blank=False, null=False)
date = models.DateField(blank=False, null=False)
# then a static field for each metric is added that corresponds to a 'metric_id' in the table 'metrics':
metric_01 = models.FloatField(default=0.0, null=False)
metric_02 = models.FloatField(default=0.0, null=False)
metric_03 = models.FloatField(default=0.0, null=False)
...
class Meta:
verbose_name_plural = "Daily Data"
db_table = "daily_data"
Later on, the Javascript code iterates over all 'metrics' to display them with the corresponding values from a requested 'daily_data' entry. Here is a small example:
let resp = await axios.get(`${API_URL}/daily_data/?location=berlin&date=2021-01-07`);
let data = resp.data[0];
METRICS.forEach(metric => {
let name = metric.name;
let description = metric.description;
let value = data[metric.metric_id];
$content.append(
` <div class="row">
<span>${name}:</span>
<span>${value}</span>
<span>${description}"</span>
</div> `
);
...
}
For the case that all metrics are pre-defined, the application is running fine. If I want to add a new metric, I create a new row in the database table 'metrics', then add the field manually to the 'DailyData' model from above, and finally restart the server.
However, my problem now is that I need the possibility to add new metrics dynamically. I.e. if a user adds a new metric (for example with a POST request), the metric should be added as a column to all existing 'daily_data' entries and should be displayed as an additional field on the website.
The intention is basically something like this (I know that this won't work, but just to get the idea):
def onNewMetricCreation(newMetric):
metric_id = newMetric.metric_id
new_field = models.FloatField(default=0.0, null=False)
DailyData.appendField(metric_id, new_field)
Is there a way to achieve this and add these model fields dynamically? Or is my whole data structure faulty for this case?
Edit: To solve the problem I've actually changed my data structure a bit. I've added a MetricsData model that connects the DailyData with the Metrics and contains the corresponding values. This allows each DailyData object to have a different number of metrics and new ones can be added easily.
The new models look like this:
class DailyData(models.Model):
location = models.ForeignKey("Locations", on_delete=models.CASCADE, blank=False, null=False)
date = models.DateField(blank=False, null=False)
class MetricsData(models.Model):
data_entry = models.ForeignKey("DailyData", on_delete=models.CASCADE, related_name="data_entry")
metric = models.ForeignKey("Metrics", on_delete=models.CASCADE)
value = models.FloatField(default=0.0, null=False)
class Metrics(models.Model):
metric_id = models.CharField(max_length=255, primary_key=True)
...
If I understood you correct I belive you're looking for a ForeignKey(). You would add this to your model:
class DailyData(models.Model):
metrics = models.ForeignKey(Metrics, on_delete=models.CASCADE)
Go inside django admin and I think you'll understand how ForeignKeys work. It's a reference to the metrics instance. Ps. don't add this field dynamically, that's probably impossible. But with this you can simply add another row.
So if you reference an instance of metrics. And then change that. all daily_data that references that will be "changed" since they're still referenceing the same instance.
If you need to reference more the one metrics use ManyToMany
I strongly recommend that you add a Foreign Key for DailyData to Metrics model.
class Metrics(model.Model):
...
related_day = models.ForeignKey(DailyData, on_delete=models.CASCADE, related_name="metrics", related_query_name="metrics", null=True)
Now you also need to add a signal to trigger after creating a metric to connect that metric to its related data.
#receiver(post_save, sender=Metrics)
def add_to_daily_data(sender, instance, created, **kwargs):
if created:
# Put your logic to add a specific metric to a daily data
Also, this way you can access all metrics data related to specific DailyData objects hassle-free.
daily_data.metrics.all()
I have two models of Student and Parent
Student models.py:
class StudentInfo(models.Model):
admissionNumber = models.BigIntegerField(primary_key=True,default=0)
firstName = models.CharField(max_length=20)
lastName = models.CharField(max_length=20)
fullName = models.CharField(max_length=50)
gender = models.CharField(max_length=20)
dob = models.DateField(null=True)
classSection = models.CharField(max_length=20)
Parent models.py
class ParentInfo(models.Model):
student = models.OneToOneField(StudentInfo,primary_key=True, on_delete=models.CASCADE)
fatherName = models.CharField(max_length=20)
motherName = models.CharField(max_length=20)
I have a form to search students through their fatherName.
So, what I want is to filter those students whose father's name contains 'some name'.
I tried this but it resultes in query set of ParentInfo:
parentInfo = ParentInfo.objects.all()
studentsInfo = parentInfo.filter(parent__fName = fName).select_related('student')
You should filter the opposite way, like:
StudentInfo.objects.filter(parentinfo__fatherName='name of father')
You here thus obtain a QuerySet of StudentInfos which contains zero, one, or more StudentInfos where there is a related ParentInfo object where the fatherName field is, in this case 'Name of father'.
Note: It might be better to implement a ForeignKey in the opposite order, such that multiple students can refer to the same ParentInfo object. Right now, a ParentInfo object can refer to exactly one StudentInfo. If there are students with the same parents (so siblings), then you introduce data duplication in the database.
# You can use contains attribute on the field of model and your query can be like this
student = models.ParentInfo.objects.values('student__firstName', 'student__lastName').filter(fatherName__contains='your value')
print(student[0]['student__firstName'])
print(student[0]['student__lastName'])
I am creating a blog application using Django and I am also very much new to django.
This is the models I created
class categories(models.Model):
Title = models.CharField(max_length=40, default='GST')
class Blog(models.Model):
User = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE,null=True,blank=True)
Date = models.DateTimeField(default=datetime.now)
Blog_title = models.CharField(max_length=255)
likes = models.ManyToManyField(settings.AUTH_USER_MODEL,related_name='likes',blank=True)
Description = RichTextUploadingField(blank=True, null=True,config_name='special')
Blog_image = models.ImageField(upload_to='blog_image', null=True, blank=True)
Category = models.ForeignKey(categories,on_delete=models.CASCADE,related_name='blogs')
I was wondering How to count the total no of blog present under a particular category?
I want to track a specific count rate for all Categories...
Done something like this in my model
def categories_count(self):
for a in categories.objects.all():
categories_count = Blog.objects.filter(Category__Title=a.Title).count()
return categories_count
But it is returning only one value...Can anyone suggest me with some suitable codes to resolve this...
Thank you
You can get a list of tuples of category title and blog count with the following query:
categories.objects.annotate(blog_count=Count('Categories')).values_list('Title', 'blog_count')
I've the below inefficient 'destroy' method for deleting Ratings that are held in Stimulus which itself is held within Experiment (I have simplified my models, for reasons of clarity).
Could you advise on a more efficient way of achieving this?
class Rating(models.Model):
rater = TextField(null=True)
rating = FloatField(null=True)
created = models.DateTimeField(null=True)
class Stimulus(TimeStampedModel):
genes = TextField()
weights = ListField()
ratings = ManyToManyField(Rating, null=True)
evaluation = FloatField(null=True)
complete = BooleanField(default=False)
Class Experiment(models.Model):
all_individuals = ManyToManyField(Stimulus, null=True)
def destroy(self):
all_ratings = Rating.objects.all()
for ind in self.all_individuals.all():
ratings = ind.ratings.all()
for rating in ratings:
if rating in all_ratings:
Rating.objects.filter(id = rating.id).delete()
Background: I am using Django to run an experiment (Experiment) which shows Users many Stimuli (Stimulus). Each Stimulus gets rated many times. Thus, I need to save multiple ratings per stimulus (and multiple stimuli per experiment).
Some simple improvements
Remove the if rating in all_ratings, every rating will be in the list of all ratings
Do the delete on the database side
ind.ratings.all().delete()
Use prefetch_related to get the foreign key objects
self.all_individuals.prefetch_related('ratings'):
Combined would be:
def destroy(self):
for ind in self.all_individuals.prefetch_related('ratings'):
ratings = ind.ratings.all().delete()
I think that in this case using ManyToManyField isn't the best choice.
You'll have less problems using common ForeignKey's changing a little the structure of this models.
Eg.
class Rating(models.Model):
rater = TextField(null=True)
rating = FloatField(null=True)
created = models.DateTimeField(null=True)
stimulus = models.ForeignKey('Stimulus', related_name='ratings')
class Stimulus(TimeStampedModel):
genes = TextField()
weights = ListField()
#ratings = ManyToManyField(Rating, null=True)
evaluation = FloatField(null=True)
complete = BooleanField(default=False)
experiment = models.ForeignKey('Experiment', related_name='stimulus')
class Experiment(models.Model):
#all_individuals = ManyToManyField(Stimulus, null=True)
name = models.CharField(max_length=100)
This is a more clear structure and when you delete Experiment by, experiment_instance.delete() a delete cascade will delete all other related models.
Hope it helps.
I hope this is not a duplicate question. I am trying to setup models in django.
In model 1 I have one kind items (parts), these can together form item type 2 (car).
I get the prices for all of these from outside interface to a model prices.
How can I setup the relationship between price - > part and price - > car.
I do not know when I get the prices if the ident belongs to car och part.
class parts(models.Model):
ident = models.CharField("IDENT", max_length = 12, unique = True, primary_key = True)
name = models.CharField(max_length=30)
class car(models.Model):
ident = models.CharField("IDENT", max_length = 12, unique = True)
start_date = models.DateField()
end_date = models.DateField()
parts= models.ManyToManyField(parts)
class Prices(models.Model):
ident= models.CharField(max_length=12)
price = models.DecimalField(max_digits=10, decimal_places= 4)
date = models.DateField()
def __unicode__(self):
return self.ident
class Meta:
unique_together = (("ident", "date"),)
I would imagine you would not store price in your model since you need this to be 100% real time. So you have;
car models.py
from parts.models import parts
name = models.CharField(max_length=100)
parts = models.ManyToManyField(parts)
Hopefully you're not trying to develop like a full scale autozone type deal, but if it's simply a car model object that is comprised of many parts than this is the basic setup you would want. having the many to many relationship to parts allows one car to have many parts. parts can belong to many cars. You don't have to specify a manytomany relationship in the parts model as the two way communication will already be handled in your cars model.
As far as price is concerned you could have a price database field in your parts model, but once again if this needs to be real time, you probably want to request that price via an api and display it directly in your webpage.