suppose I have the following three models, see as follow: I wanna to construct a Django model query to archive the same effect as the following SQL statement.
SQL statement
select B.value, C.special
from B inner join C
where B.version = C.version and B.order = C.order;
I got the following three models:
class Process(models.Model):
name = models.CharField(max_length=30)
description = models.CharField(max_length=150)
class ProcessStep(models.Model):
process = models.ForeignKey(Process)
name = models.CharField(max_length=30)
...
order = models.SmallIntegerField(default=1)
version = models.SmallIntegerField(null=True)
class Approve(models.Model):
process = models.ForeignKey(Process)
content = models.CharField(max_length=300)
...
version = models.SmallIntegerField(null=True)
order = models.SmallIntegerField(default=0)
I want to find all Approves that have the same (version, order) tuple matching against the ProcessStep model.
Something like this?
Approve.objects.filter(process__processstep_set__order=<value>)
Right now I can only come out with a solution by using raw SQL, see the following code.
from django.db import connection
cursor = connection.cursor()
cursor.execute("
SELECT A.id, B.id
from approval_approve as A inner join approval_approvalstep as B
where A.process_id = B.process.id
and A.order = B.order
and A.version = B.version;")
# do something with the returned data
If you guys got any better solution, I would like to hear from you, thanks~
Related
Hi i have two models like this,
class Sample(models.Model):
name = models.CharField(max_length=256) ##
processid = models.IntegerField(default=0) #
class Process(models.Model):
sample = models.ForeignKey(Sample, blank=False, null=True, on_delete=models.SET_NULL, related_name="process_set")
end_at = models.DateTimeField(null=True, blank=True)
and I want to join Sample and Process model. Because Sample is related to process and I want to get process information with sample .
SELECT sample.id, sample.name, process.endstat
FROM sample
INNER JOIN process
ON sample.processid = process.id
AND process.endstat = 1;
(i'm using SQLite)
I used
sample_list = sample_list.filter(process_set__endstat=1))
but it returned
SELECT sample.id, sample.name
FROM sample
INNER JOIN process
ON (sample.id = process.sample_id)
AND process.endstat = 1)
This is NOT what I want.
How can i solve the problem?
This should work for you
Process.objects.filter(end_at=1).values('sample__id','sample__name','end_at')
.values() method returns selective table fields.
I'm assuming sample_list = Sample.objects.
When you are filtering a model, only the fields defined in the model are selected. In your example, id and processid. If you want to retrieve values from related models as a single record you need to use values or values_list. To get the desired query you have to do this
sample_list = sample_list.filter(process_set__endstat=1).values('id', 'name', 'process__endstat')
Btw, Django does JOIN on the foreign key field. So, you can't get ON sample.processid = process.id since processid is not a ForeignKey field.
Reference:
https://docs.djangoproject.com/en/4.0/ref/models/querysets/#values
I found JOIN not on foreign key field in django.
sample_list = sample_list.filter(processid__in=Process.objects.filter(endstat=1)
I used the medthod of
Django-queryset join without foreignkey
I fairly new to Django and stuck with creating a left join in Django. I tried so many, but none of them seems to be working:
The query I want to translate to Django is:
select ssc.id
,mgz.Title
,tli.id
,tli.Time
from Subscription ssc
join Person prs
on ssc.PersonID = prs.id
and prs.id = 3
join Magazine mgz
on mgz.id = ssc.MagazineID
and mgz.from <= date.today()
and mgz.until > date.today()
left join TimeLogedIn tli
on tli.SubscriptionID = ssc.id
and tli.DateOnline = date.today()
The model I'm using looks like this:
class Magazine(models.Model):
Title = models.CharField(max_length=100L)
from = models.Datefield()
until = models.Datefield()
Persons = models.ManyToManyField(Person, through='Subscription')
class Person(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
Magazines = models.ManyToManyField(Magazine, through='Subscription')
class Subscription(models.Model):
MagazineID = models.ForeignKey(Magazine,on_delete=models.CASCADE)
PersonID = models.ForeignKey(Person,on_delete=models.CASCADE)
class TimeLogedIn(models.Model):
SubscriptionID = models.ForeignKey('Subscription', on_delete=models.CASCADE)
DateOnline = models.DateField()
Time = models.DecimalField(max_digits=5, decimal_places=2)
Like I said, tried so many but no succes and now I don't know how to do this in Django ORM , is it even possible? I created already a raw-query and this is working ok, but how to create this in Django ORM?
You can use field lookups lte and gt to filter your objects and then values() method.
You can also querying in the opposite direction and use Q objects for null values:
from django.db.models import Q
Subscription.objects.filter(
PersonID_id=3,
MagazineID__from__lte=date.today(),
MagazineID__until__gt=date.today()
).filter(
Q(TimeLogedIn__DateOnline=date.today()) | Q(TimeLogedIn__DateOnline__isnull=True)
).values("id", "MagazineID__Title", "TimeLogedIn__id", "TimeLogedIn__Time")
OR from TimeLogedIn:
TimeLogedIn.objects.filter(DateOnline=date.today()).filter(
SubscriptionID__MagazineID__from__lte=date.today(),
SubscriptionID__MagazineID__util__gt=date.today()
).values(
"SubscriptionID_id", "SubscriptionID__MagazineID__Title", "id", "Time"
)
Querysets also have the query attribute that contains the sql query to be executed, you can see it like following:
print(TimeLogedIn.objects.filter(...).values(...).query)
Note: Behind the scenes, Django appends "_id" to the field name to create its database column name. Therefore it should be
subscription, instead of SubscriptionID.
You can also use prefetch_related() and select_related() to prevent multiple database hits:
SubscriptionID.objects.filter(...).prefetch_related("TimeLogedIn_set")
SubscriptionID.objects.filter(...).select_related("PersonID")
I'm new in Django. So, I want to join two models which are company and client and count the number of clients for each of the company. Here the SQL
SELECT Company_company.name, count(Client_client.cid)
FROM Company_company
LEFT JOIN Client_client
ON Company_company.comid = Client_client.comid_id
GROUP BY Company_company.name;
But since in Django, we use ORM. So I'm a little bit confusing since I'm a beginner. I already refer few SQL to ORM converter website such as Django ORM and do some try and error. But, I didn't know where the problem since I want the output from the ORM to be classified into a different array. Here is my code:
labels = []
data = []
queryClientCompany = client.objects.values('comid').annotate(c=Count('cid')).values('comid__name','c')
for comp in queryClientCompany:
labels.append(comp.comid__name)
data.append(comp.c)
Here some of the relevant things in the client and company models:
class client (models.Model):
#client info
cid = models.AutoField(primary_key = True)
comid = models.ForeignKey(company,related_name='companys',
on_delete = models.DO_NOTHING,verbose_name="Company",null = True, blank = True)
class company(models.Model):
comid = models.AutoField(_('Company'),primary_key = True)
#company info
name = models.CharField(_('Company Name'),max_length = 50)
The error stated that the comid__name is not defined. So actually how to append the result? I hope someone can help me. Thank you for helping in advanced.
You should query from the opposite side to perform the LEFT OUTER JOIN between company and client (and not client and company):
from django.db.models import Count
labels = []
data = []
queryClientCompany = company.objects.annotate(
c=Count('companys__cid')
)
for comp in queryClientCompany:
labels.append(comp.name)
data.append(comp.c)
The companys part is due to the related_name='copanys', but it does not make much sense to name this relation that way. The related_name=… parameter [Django-doc] specifies how to access the Clients for a given Company, so clients is a more appropriate value for the related_name:
class client (models.Model):
cid = models.AutoField(primary_key=True)
comid = models.ForeignKey(
company,
related_name='clients',
on_delete = models.DO_NOTHING,
verbose_name="Company",
null = True,
blank = True
)
then the query is:
from django.db.models import Count
labels = []
data = []
queryClientCompany = company.objects.annotate(
c=Count('clients__cid')
)
for comp in queryClientCompany:
labels.append(comp.name)
data.append(comp.c)
I have a model:
class Distributor(models.Model):
...
#property
def full_name(self):
return self.name + self.surname
class UserProfile(AbstractUser):
links = models.ManyToManyField(
Link, blank=True, related_name='links_by_user')
distributors = models.ManyToManyField(
Distributor, blank=True, related_name='distributors_of_user')
Now I want to make a query like this:
dist_list=request.user.distributors.all().filter(full_name__icontains='')
But this isn't working.
How to make such a query?
Django filters run at the database level. So it isn't possible to what you would like.
Keep in mind that you can always fall back to SQL if you'd like. No need to spend a ton of time figuring out how to make the Django ORM do this when it is a trivial SQL query:
query = """
SELECT *
FROM distributor_distributor d
INNER JOIN user_user_profile up ON up.id = %(user_id)s
INNER JOIN user_user_distributors_of_user udu ON udu.user_profile_id = %(user_id)s
AND udu.distributor_id = d.id
WHERE d.name || d.surname = %(query)s;
"""
dist_list = Distributor.objects.raw(query, {'user_id': request.user.pk, 'query': 'hello world'})
Wrap that in a function, put it in a utils.py module or something, baby you've got a stew going!
What you want to do is not possible. If you want to do that, you would have to do the filtering in python (with something like a list comprehension), like this:
[d for d in request.user.distributors.all() if ''.lower() in d.full_name().lower()]
Doing this would almost definitely be slower than querying the database, however, if request.user.distributors.all() has very many entries.
However, in this specific case, you could probably split up the string you want to query with into first and last name and query each separately? Maybe something like:
request.user.distributors.all().filter(name__icontains=name | surname__icontains=surname)
I have the following models:
class AcademicRecord(models.Model):
record_id = models.PositiveIntegerField(unique=True, primary_key=True)
subjects = models.ManyToManyField(Subject,through='AcademicRecordSubject')
...
class AcademicRecordSubject(models.Model):
academic_record = models.ForeignKey('AcademicRecord')
subject = models.ForeignKey('Subject')
language_group = IntegerCharField(max_length=2)
...
class SubjectTime(models.Model):
time_id = models.CharField(max_length=128, unique=True, primary_key=True)
subject = models.ForeignKey(Subject)
language_group = IntegerCharField(max_length=2)
...
class Subject(models.Model):
subject_id = models.PositiveIntegerField(unique=True,primary_key=True)
...
The academic records have list of subjects each with a language code and the subject times have a subject and language code.
With a given AcademicRecord, how can I get the subject times that matches with the AcademicRecordSubjects that the AcademicRecord has?
This is my approach, but it makes more queries than needed:
# record is the given AcademicRecord
times = []
for record_subject in record.academicrecordsubject_set.all():
matched_times = SubjectTime.objects.filter(subject=record_subject.subject)
current_times = matched_times.filter(language_group=record_subject.language_group)
times.append(current_times)
I want to make the query using django ORM not with raw SQL
SubjectTime language group has to match with Subject's language group aswell
I got it, in part thanks to #Robert Jørgensgaard Eng
My problem was how to do the inner join using more than 1 field, in which the F object came on handly.
The correct query is:
SubjectTime.objects.filter(subject__academicrecordsubject__academic_record=record,
subject__academicrecordsubject__language_group=F('language_group'))
Given an AcademicRecord instance academic_record, it is either
SubjectTime.objects.filter(subject__academicrecordsubject_set__academic_record=academic_record)
or
SubjectTime.objects.filter(subject__academicrecordsubject__academic_record=academic_record)
The results reflect all the rows of the join that these ORM queries become in SQL. To avoid duplicates, just use distinct().
Now this would be much easier, if I had a django shell to test in :)