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 :)
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)
Models.py:
class ScoringModel(models.Model):
title = models.CharField(max_length=64)
class PredictedScore(models.Model):
job = models.ForeignKey('Job')
candidate = models.ForeignKey('Candidate')
model_used = models.ForeignKey('ScoringModel')
score = models.FloatField()
created_at = models.DateField(auto_now_add=True)
modified_at = models.DateTimeField(auto_now=True)
serializers.py:
class MatchingJobsSerializer(serializers.ModelSerializer):
job_title = serializers.CharField(source='job.title', read_only=True)
class Meta:
model = PredictedScore
fields = ('job', 'job_title', 'score', 'model_used', 'candidate')
To fetch the top 3 jobs, I tried the following code:
queryset = PredictedScore.objects.filter(candidate=candidate)
jobs_serializer = MatchingJobsSerializer(queryset, many=True)
jobs = jobs_serializer.data
top_3_jobs = heapq.nlargest(3, jobs, key=lambda item: item['score'])
Its giving me top 3 jobs for the whole set which contains all the models.
I want to fetch the jobs with top 3 scores for a given candidate for each model used.
So, it should return the top 3 matching jobs with each ML model for the given candidate.
I followed this answer https://stackoverflow.com/a/2076665/2256258 . Its giving the latest entry of cake for each bakery, but I need the top 3.
I read about annotations in django ORM but couldn't get much about this issue. I want to use DRF serializers for this operations. This is a read only operation.
I am using Postgres as database.
What should be the Django ORM query to perform this operation?
Make the database do the work. You don't need annotations either as you want the objects, not the values or manipulated values.
To get a set of all scores for a candidate (not split by model_used) you would do:
queryset = candidate.property_set.filter(candidate=candidate).order_by('-score)[:2]
jobs_serializer = MatchingJobsSerializer(queryset, many=True)
jobs = jobs_serializer.data
What you're proposing isn't particularly well suited in the Django ORM, annoyingly - I think you may need to make separate queries for each model_used. A nicer solution (untested for this example) is to hook Q queries together, as per this answer.
Example is there is tags, but I think holds -
#lets get a distinct list of the models_used -
all_models_used = PredictedScore.objects.values('models_used').distinct()
q_objects = Q() # Create an empty Q object to start with
for m in all_models_used:
q_objects |= Q(model_used=m)[:3] # 'or' the Q objects together
queryset = PredictedScore.objects.filter(q_objects)
I am using Django framework, appengine database.
My code for model is:
class Group(models.Model):
name = models.CharField(max_length=200)
ispublic = models.BooleanField()
logo = models.CharField(max_length=200)
description = models.CharField(max_length=200)
groupwebsite = models.CharField(max_length=200)
owner = models.ForeignKey('profile')
class Group_members(models.Model):
profile = models.CharField(max_length=200)
group = models.ForeignKey('group')
I am querying on Group_members to remove group. My query is as follows:
groups = Group_members.objects.filter(Q(profile=profile.id),~Q(group__in=group_id)
INFO:
group_id = ['128','52']
group is a foreign key to group model
My problem is when I run this query, it throws Database error: Lookup type 'in' can't be negated.
I have also performed query using __in it worked fine but does not work for foreign key.
Thanks in advance
I think you trying to filter profile id and remove groups in group_id in single filter
groups = Group_members.objects.filter(Q(profile=profile.id),~Q(group__in=group_id)
instead try this:
1)first filter the profiles form group_member :
groups = Group_members.objects.filter(profile=profile.id)
2)remove the groups form Queryset by:
groupId = [x.group.id for x in groups if x.group.id not in group_id]
Hope this will give you perfect result
2 suggestions.
Use ~Q(group__ pk__in=group_id)
Instead of using filter and not in, use exclude and in