Django querysets - Performing subqueries - django

How to make query to get all components added by a certain user? Also in the resulting object I want to have the system name and project name too. I saw examples demonstrating sub-queries for two tables, but I need this for 3 tables.
Thank you.
class component(models.Model):
id = models.AutoField(primary_key=True)
server = models.ForeignKey(server, on_delete="CASCADE")
name = models.TextField(blank=True)
comments = models.TextField()
timestamp = models.DateTimeField(auto_now=True)
class system(models.Model):
id = models.AutoField(primary_key=True)
project = models.ForeignKey(project, on_delete="CASCADE")
name = models.CharField(max_length=255,blank=True)
comments = models.TextField()
timestamp = models.DateTimeField(auto_now=True)
class project(models.Model):
id = models.AutoField(primary_key=True)
name = models.CharField(max_length=255,blank=True)
comments = models.TextField()
user = models.ForeignKey(User, on_delete="CASCADE")
timestamp = models.DateTimeField(auto_now=True)

No need to use subqueries here, we can simply perform joins, by looking "through" foreign keys (this is typically denoted with two consecutive underscores __ in Django).
If you want So all the Components that belong to a System that belongs to a Project that belongs to a user, we can query this with:
from django.db.models import F
Component.objects.filter(
system__project__user=someuser
).annotate(
system_name=F('system__name'),
project_name=F('system__project__name')
)
with someuser the user you want to filter with.
The components in this queryset will have extra attributes system_name and project_name that contain the name of the system and the project respectively.

Related

Filtering Django query filtering

I'm doing some querying currently and I was wondering if I would be able to query something from these 3 models where the return would give me all the projects the users are working on. I know about the basic filtering however thats not really enough in this case, how would one go about querying through 2 foreign keys.
class User(models.Model):
first_name = models.CharField(max_length=255)
last_name = models.CharField(max_length=255)
email = models.EmailField()
class ProjectUser(models.Model):
project = models.ForeignKey("Project", on_delete=models.CASCADE)
user = models.ForeignKey("User", on_delete=models.CASCADE)
is_lead = models.BooleanField(default=False)
class Meta:
unique_together = (("project", "user"),)
class Project(models.Model):
name = models.CharField(max_length=255)
client = models.CharField(max_length=255)
complete = models.BooleanField(default=False)
You can obtain the Projects a user is working on with:
Project.objects.filter(
projectuser__user=user
)
The double underscores are used to look "through" relations. Furthermore the default related_query_name=… parameter [Django-doc] is, if not specified, the name of the model in lowercase.

How to fetch translation record in django

I am new in django framework.I have 3 tables in mysql database. I want to fetch data from main table with translation table and images table.
My model.py
class Country(models.Model):
#id = models.IntegerField(primary_key=True)
iso_code = models.CharField(max_length=2, unique=True)
slug = models.CharField(max_length=255, unique=True)
is_featured = models.IntegerField(max_length=1)
class Meta:
db_table = 'rh_countries'
class CountryTranslation(models.Model):
country_id = models.ForeignKey(Country, on_delete=models.CASCADE)
name = models.CharField(max_length=255)
description = models.TextField(blank=True, null=True)
locale = models.CharField(max_length=2)
class Meta:
db_table = 'rh_countries_translations'
class CountryImage(models.Model):
country_id = models.ForeignKey(Country, on_delete=models.CASCADE)
image = models.CharField(max_length=255)
is_main = models.IntegerField(max_length=1)
class Meta:
db_table = 'rh_country_images'
Now I want to fetch all country with translation record by locale and associated image.
Please give a solution if anyone know.
You can do this by using a filtering, and annotate:
from django.db.models import F
Country.objects.filter(
countrytranslation__locale=mylocale
).annotate(
name=F('countrytranslation__name')
)
This will result in a QuerySet with all Countrys (that have a Translation for the given mylocale). These Countrys will have an extra attribute .name that is the translated name of the Country.
So given the translations exist, then for mylocale='en', this will result in a QuerySet, with Country(name='Germany', iso_code='de'), and for mylocale='de', it will result in Country(name='Deutschland', iso_code='de') (here this is a bit an ad hoc format, to demonstrate how it works).
Note: ForeignKeys typically do not end with _id. Django will automatically add an _id suffix to the database column. The foreign key itself is on the Python/Django level represented as a lazy loaded attribute.

Django spanning relationships

I've read the documentation but am still coming up with errors. I have Users placing Orders for Catalog objects. I'd like to create a query which returns all Users that have an Order containing a specific Catalog item.
Here are my models:
class Catalog(models.Model):
name = models.CharField(max_length=100)
price = models.IntegerField()
def __unicode__(self):
return self.name
class Annual(models.Model):
catalog = models.OneToOneField(Catalog, blank=True, null=True, related_name='annual_products')
year_id = models.IntegerField(max_length=4)
start_date = models.CharField(max_length=10)
end_date = models.CharField(max_length=10)
date = models.DateTimeField(auto_now_add=True, blank=True)
def __unicode__(self):
return unicode(self.year_id)
class Order(models.Model):
user = models.ForeignKey(User, related_name='who_ordered')
select = models.ManyToManyField(Catalog, related_name='annuals_ordered', blank=True, null=True)
def __unicode__(self):
return unicode(self.user)
Here is the query I've been trying:
Catalog.objects.filter(order__select__annual='2014')
If you need users, you should start with users. Also, you need to filter on a specific field in Annual, ie year_id.
User.objects.filter(order__select__annual__year_id=2014)
If I got your question correctly then, your query is wrong. There is no attribute name order inside your Catalog model, then how can you use it for filtering ? Or I'm missing anything here ?
Directly using the related name references on the related fields, you can get the users by using -
# id is auto generated field or you can pass one annual_product object.
User.objects.filter(who_ordered__select__annual_products__id=1)
# OR
annual = Annual.objects.all()[0]
User.objects.filter(who_ordered__select__annual_products=annual)
The step by step how you can achieve the same :-
# where 1 is the id of an one object in Catalog model.
# You can pass Catalog object also to filter the users
Order.objects.filter(select__id=1)
# Here is the full query
catalog = Catalog.objects.all()[0]
orders = Order.objects.filter(select=catalog)
users = [o.user for o in orders] # This loop isn't necessary.
Now you have all orders specific to one Catalog, from this you can get the user object by using the user attribute in each order.

How to find the name of the user with whom the file is shared?

I have a file, user and share models like this:
class File(models.Model):
users = models.ForeignKey(User)
file_name = models.CharField(max_length=100)
type = models.CharField(max_length=10)
source = models.CharField(max_length=100)
start_date = models.TextField()
time_overview = models.CharField(max_length=55)
end_date = models.TextField()
duration = models.TextField()
size_overview = models.IntegerField()
size = models.TextField()
flag = models.TextField()
flag_r = models.TextField()
class Share(models.Model):
users = models.ForeignKey(User)
files = models.ForeignKey(File)
shared_user_id = models.IntegerField()
shared_date = models.TextField()
I found out the number of users with whom the particular file is shared using this query:
shared_file = File.objects.filter(id__in= Share.objects.filter(users_id = log_id).values_list('files', flat=True)).annotate(count=Count('share__shared_user_id'))
Now, I want to find out the users name with whom the particular file is shared.
Tried using this:
shared_username = User.objects.filter(id__in= Share.objects.filter(users_id = log_id).values_list('shared_user_id', flat=True))
Didn't get it right. I want to get the username with whole the particular files are shared. How can I do this?
Add the condition of a particular file name in the second queries:
shared_username = User.objects.filter(id__in = Share.objects.filter(users_id = log_id, files__file_name='file1').values_list('shared_user_id', flat=True))
However your model has some problems worth noting:
1- If you replace Share.shared_user_id with a OnetoMany field your model would be more correct and your queries a lot easier.
2- If you use related_name on your foreign keys you can access them from the opposite model and your queries would be much easier.
3- You should not use plural var names for foreign keys as they represent one object. File.users should be File.user and the same for Share.files and Share.users
4- Your model could be a lot more readable if you name your vars properly. For example instead of File.users you could use File.owner or File.owning_user. Same with Share.users: Share.sharing_user.

constructing a joined django query

I'm interacting with a legacy db on another system, so the models are written in stone and not very django-ey.
My models.py:
class Site(models.Model):
site_code = models.CharField(max_length=30, primary_key=True)
name = models.CharField(unique=True, max_length=300)
class Document(models.Model):
id = models.IntegerField(primary_key=True)
site_ref = models.ForeignKey(Site)
description = models.CharField(max_length=1500)
class DocumentStatusCategory(models.Model):
id = models.IntegerField(primary_key=True)
name = models.CharField(unique=True, max_length=90)
class DocumentStatus(models.Model):
id = models.IntegerField(primary_key=True)
document = models.ForeignKey(Document)
status = models.ForeignKey(DocumentStatusCategory)
changed_by = models.ForeignKey(User)
created_at = models.DateTimeField()
In my views.py I want to retrieve a queryset with all the Document objects that belong to a specified Site (say site_ref=mysite) which do not have any related DocumentStatus objects with status=4.
Any idea how I can do this as a single (non-sql intensive) line?
Document.objects.filter(site_ref=mysite).exclude(documentstatus__status_id=4)
Document.objects.filter(site_ref=site_obj).exclude(documentstatus_set__in=DocumentStatus.objects.filter(status_id=4))
Not exactly one query, but I don't think that's achievable without going down to raw sql. Two queries isn't bad though I suppose.
I should mention that the above assumes that the reverse relation between Document and DocumentStatus is documentstatus_set. You can explicitly state what the reverse relation is like so:
# inside the DocumentStatus model definition
document = models.ForeignKey(Document, related_name='document_statuses')
Then the query becomes:
Document.objects.filter(site_ref=site_obj).exclude(document_statuses__in=DocumentStatus.objects.filter(status_id=4))