I have about 5 tables with user foreign key, i.e.:
class Passport(models.Model):
user = models.OneToOneField(User)
...
Also, classes like UserProfile, Company, UserOptions, NotifySettings, etc. I need to get dict with joined values for user-summary page. Also i need to join to this union this summary stats:
rent_sums = WriteOff.objects.filter(created_at__range=(rent_start, rent_finish), write_off_type='rent').values('user').\
annotate(rent_amount=Sum('amount')).order_by()
How can i do it without manualy update of a result dict?
you can do this by executing a custom SQL from django but the main problem I see here is the way the models are been handled, it would be a lot easier if you mixed all this user foreign keys to be in the UserProfile, for example:
class UserProfile(models.Model):
user = fields.OneToOneField(User)
company = fields.ForeignKey(Company)
options = fields.ForeignKey(Options)
notification_settings = fields.ForeignKey(NotifySettings)
...
This way you can use the ORM django brings with more ease. In my opinion it would be faster for you to create a migration instead of this huge query.
Related
I have three models
class A(Model):
...
class B(Model):
id = IntegerField()
a = ForeignKey(A)
class C(Model):
id = IntegerField()
a = ForeignKey(A)
I want get the pairs of (B.id, C.id), for which B.a==C.a. How do I make that join using the django orm?
Django allows you to reverse the lookup in much the same way that you can use do a forward lookup using __:
It works backwards, too. To refer to a “reverse” relationship, just use the lowercase name of the model.
This example retrieves all Blog objects which have at least one Entry whose headline contains 'Lennon':
Blog.objects.filter(entry__headline__contains='Lennon')
I think you can do something like this, with #Daniel Roseman's caveat about the type of result set that you will get back.
ids = B.objects.prefetch_related('a', 'a__c').values_list('id', 'a__c__id')
The prefetch related will help with performance in older versions of django if memory serves.
Suppose I have the following model:
class User(models.Model):
blogs = model.ManyToManyField(Blog)
What is the best way to add a blog to the field for multiple users e.g. I want to add an instance of Blog called blog to all users (i.e. User.object.all()). Do I have to iterate over each result individually or is there a way to do it all at once?
Thanks.
You could do a bulk_create on the through table. For example:
blog = Blog.objects.get(…)
users = User.object.all()
User.blogs.through.objects.bulk_create(
[User.blogs.through(user_id=user.pk, blog_id=blog.pk) for user in users]
)
That will do one database query.
I am trying to make a query that selects all uuids of ProblemSet whose problems contains at least one problem with a specific problem type. How can I do it in Django? In mysql it will be a simple join but django's '__contains' doesn't serve the needs..
Thanks!!
class ProblemType:
name ..... (many fields)
class Problem:
problem_type = models.ManyToManyField(ProblemType)
...... (many fields)
class ProblemSet:
problems = models.ManyToMnayField(Problem)
uuid = models.CharField(...)
...... (many fields)
Does a normal filter not work?
uuids = ProblemSet.objects.filter(problems__problem_type__name='MyProblemType')
.values_list('uuid', flat=True)
Also, do your problems have multiple problem_types? If so, then you should reflect that fact by renaming your ManyToManyField as problem_types (note the pluralization). Otherwise, you shouldn't use a ManyToManyField.
I need to make a smart menu, for which I need a ManyToMany relation.
My model is:
from django.db import models
class Health_plan(models.Model):
a = models.IntegerField ()
b = models.IntegerField ()
class Doctors_list(models.Model):
name = models.CharField(max_length=30)
hp_id = models.ManyToManyField(Health_plan)
def __unicode__(self):
return self.name
How do I make this relation in the database ? I was thinking in puting the health_plans (a,b) as columns, and the doctors as rows, with 0s and 1s to identify their covered health_plans.
Someone told me this was a misuse of a ManyToManyField, I don't know wich step to take.
Help appreciated
The approach of puting the health_plans as columns is not necessarily wrong, but it implies that you have a fixed number of health plans and that you will never add a new one.
The traditional approach for many-to-many relationships in relational databases is to introduce a table in the middle. This table will just contain the association between a doctor and a health plan.
If you have a Doctor table that contains:
id name
1 foo
2 bar
And a HealthPlan table:
id model
1 a
2 b
You then add a table Doctor_HealthPlan that is like:
doctor_id healthplan_id
1 2
2 1
2 2
The ManyToMany field type in django will automatically create this table for you. Your code is correct, but you should probably rename hp_id to something like health_plans, since it is a proxy that allows you to access the list of health plans associated to a doctor.
Django's ORM already takes care of the intermediate table so you don't have to "make this relation(ship) in the database", but given your question you obviously need to learn about proper relational model normalisation - if you don't understand the relational model you won't get nowhere with Django's ORM, nor with any other sql stuff FWIW.
For the record, in the relational model, a many to many relationship is modeled as a relation ("table" in SQL) with foreign keys on both other tables, ie:
health_plan(#health_plan_id, name, ...)
doctor(#doctor_id, firstname, lastname, ...)
doctors_health_plans(#health_plan_id, #doctor_id)
So your django models should be:
class HealthPlan(models.Model):
# no need to define an 'id' field,
# the ORM provides one by default
name = models.CharField(....)
class Doctor(models.Model):
firstname = models.CharField(....)
lastname = models.CharField(....)
health_plans = models.ManyToManyField(HealthPlan, related_name="doctors")
Then you'll be able to get all HealthPlans for a Doctor :
doc = Doctor.objects.get(pk=xxxx)
doc.health_plans.all()
and all Doctors for an HealthPlan:
plan = HealthPlan.objects.get(pk=xxxx)
plan.doctors.all()
The FineManual(tm) is your friend as usual...
You just need to save the two models first then add the healthplan instance to the doctors list. Django will handle the rest for you .
For example :
doctor_list = Doctors_list(name="Bwire")
health_plan.save()
doctor_list.save()
#Then add the plan to the doctors list.
doctor_list.hp_id.add(health_plan)
Django creates the tabels for you. In your project folder run:
python manage.py syncdb
Health_plan and Doctors_list are both tables.
'a' and 'b' are columns in Health_plan. 'Name' and 'hp_id' are columns in Doctors_list.
Django will create a column for id in each table. Django will also create a table "Doctor_list_Health_plan" to store the relation information.
Django models are Python classes, so the Python naming conventions apply. Use HealthPlan and Doctor (CapitalizeWord singular).
Your field names are a bit abstract. I suggest you use more descriptive names. Eg:
class HealthPlan(models.Model):
name = models.CharField()
extra_care = models.BooleanField()
I have 2 models in my Django code:
class ModelA(models.Model):
name = models.CharField(max_length=255)
description = models.CharField(max_length=255)
created_by = models.ForeignKey(User)
class ModelB(models.Model):
category = models.CharField(max_length=255)
modela_link = models.ForeignKey(ModelA, 'modelb_link')
functions = models.CharField(max_length=255)
created_by = models.ForeignKey(User)
Say ModelA has 100 records, all of which may or may not have links to ModelB
Now say I want to get a list of every ModelA record along with the data from ModelB
I would do:
list_a = ModelA.objects.all()
Then to get the data for ModelB I would have to do
for i in list_a:
i.additional_data = i.modelb_link.all()
However, this runs a query on every instance of i. Thus making 101 queries to run.
Is there any way of running this all in just 1 query? Or at least less than the 101 queries.
I've tried putting in ModelA.objects.select_related().all() but this didn't seem to have any effect.
As Ofri says, select_related only works on forwards relations, not reverse ones.
There's no built-in way to automatically follow reverse relations in Django, but see my blog post for a technique to do it reasonably efficiently. The basic idea is to get all the related objects for every item at once, then associate them manually with their related item - so you can do it in 2 queries rather than n+1.
Django ORM is a good thing but some some things is better to do manually.
You may import connection cursor and execute raw sql in single query.
from django.db import connection
cur=connection.cursor()
cur.execute(query)
rows = cur.fetchall()
your query should look like (for MySQL)
SELECT * FROM appname_modela INNER JOIN appname_modelb ON appname_modela.id=appname_modelb.modela_link_id
The reason .select_related() didn't work, is that .select_related() is used to follow foreign keys. Your ModelA doesn't have a foreign key to ModelB. Its ModelB that has a foreign key to ModelA. (so a ModelA instance can have multiple ModelB instances related to it).
You could use this to do it in 2 queries, and a bit of python code:
list_b = ModelB.objects.all()
list_a = ModelA.objects.all()
for a in list_a:
a.additional_data = [b for b in list_b if b.modela_link_id==a.id]
from django.db.models import OuterRef, Subquery
newest = ModelB.objects.filter(modela_link=OuterRef('pk'))
ModelA.objects.annotate(newest=Subquery(newest))
https://docs.djangoproject.com/en/3.2/ref/models/expressions/#subquery-expressions