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")
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 have the following models:
class Workspace(Model):
pass
class Event(Model):
workspace = ForeignKey(Workspace)
limit = FloatField(default=0)
entity_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
entity_id = models.PositiveIntegerField()
entity = GenericForeignKey('entity_type', 'entity_id')
class Entity(Model):
events = GenericRelation(Event, content_type_field='entity_type', object_id_field='entity_id')
class Meta:
abstract = True
class SomeEntity(Entity):
pass
Now I need to build a queryset to sort objects of SomeEntity by the limit of their events inside a given Workspace
The SQL query I'm hoping to have is something like this:
SELECT
"some_entity"."id", workspace_events."id", COALESCE(workspace_events."limit", 0) AS "limit"
FROM "some_entity" LEFT OUTER JOIN "event" workspace_events
ON (
"some_entity"."id" = workspace_events."entity_id" AND
workspace_events."entity_type_id" = SOME_ENTITY_CONENT_TYPE_ID AND
workspace_events."workspace_id" = GIVEN_WORKSPACE_ID
)
) ORDER BY "limit" DESC'
Where:
SOME_ENTITY_CONTENT_TYPE_ID is the content type id of the SomeEntity model.
GIVEN_WORKSPACE_ID is the workspace id I want to filter the events on.
The queryset I'm using is this:
SomeEntity.objects.annotate(
workspace_events=FilteredRelation('events', condition=Q(events__workspace_id=GIVEN_WORKSPACE_ID)),
limit=Coalesce('workspace_events__limit', 0),
).values('id', 'workspace_events__id', 'limit').order_by('-limit')
But the query I'm getting from the above queryset doesn't include the workspace condition in the join at all!
SELECT
"some_entity"."id", workspace_events."id", COALESCE(workspace_events."limit", 0) AS "limit"
FROM "some_entity" LEFT OUTER JOIN "event" workspace_events
ON (
"some_entity"."id" = workspace_events."entity_id" AND
workspace_events."entity_type_id" = SOME_ENTITY_CONENT_TYPE_ID AND
)
) ORDER BY "limit" DESC'
What am I doing wrong? Why the workspace condition is not added to the join conditions? And if it's not possible to use FilteredRelation with generic relations then how can I produce the SQL query I want using django ORM?
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 the following working code:
houses_of_agency = House.objects.filter(agency_id=90)
area_list = AreaHouse.objects.filter(house__in=houses_of_agency).values('area')
area_ids = Area.objects.filter(area_id__in=area_list).values_list('area_id', flat=True)
That returns a queryset with a list of area_ids. I want to filter further so that I only get area_ids where there are more than 100 houses belonging to the agency.
I tried the following adjustment:
houses_of_agency = House.objects.filter(agency_id=90)
area_list = AreaHouse.objects.filter(house__in=houses_of_agency).annotate(num_houses=Count('house_id')).filter(num_houses__gte=100).values('area')
area_ids = Area.objects.filter(area_id__in=area_list).values_list('area_id', flat=True)
But it returns an empty queryset.
My models (simplified) look like this:
class House(TimeStampedModel):
house_pk = models.IntegerField()
agency = models.ForeignKey(Agency, on_delete=models.CASCADE)
class AreaHouse(TimeStampedModel):
area = models.ForeignKey(Area, on_delete=models.CASCADE)
house = models.ForeignKey(House, on_delete=models.CASCADE)
class Area(TimeStampedModel):
area_id = models.IntegerField(primary_key=True)
parent = models.ForeignKey('self', null=True)
name = models.CharField(null=True, max_length=30)
Edit: I'm using MySQL for the database backend.
You are querying for agency_id with just one underscore. I corrected your queries below. Also, in django it's more common to use pk instead of id however the behaviour is the same. Further, there's no need for three separate queries as you can combine everything into one.
Also note that your fields area_id and house_pk are unnecessary, django automatically creates primary key fields which area accessible via modelname__pk.
# note how i inlined your first query in the .filter() call
area_list = AreaHouse.objects \
.filter(house__agency__pk=90) \
.annotate(num_houses=Count('house')) \ # <- 'house'
.filter(num_houses__gte=100) \
.values('area')
# note the double underscore
area_ids = Area.objects.filter(area__in=area_list)\
.values_list('area__pk', flat=True)
you could simplify this even further if you don't need the intermediate results. here are both queries combined:
area_ids = AreaHouse.objects \
.filter(house__agency__pk=90) \
.annotate(num_houses=Count('house')) \
.filter(num_houses__gte=100) \
.values_list('area__pk', flat=True)
Finally, you seem to be manually defining a many-to-many relation in your model (through AreaHouse). There are better ways of doing this, please read the django docs.
I have two models:
class Project(models.Model):
...
class StateChange(models.Model):
created_at = models.DateTimeField(default=now, db_index=True)
project = models.ForeignKey("project.Project")
state = models.IntegerField(choices=PROJECT_STATE_TYPES, db_index=True)
...
The models are linked and I need a list of projects which is filtered by the related StateChange if there's one.
I build my queryset like this:
state_checked = Case(
When(statechange__state=PROJECT_STATE_CHECKED, then=F('statechange__created_at'))
)
state_construction_ordered = Case(
When(statechange__state=PROJECT_STATE_CONSTRUCTION_ORDERED, then=F('statechange__created_at'))
)
qs = Projekt.objects.visible_for_me(self.request.user) \
.annotate(date_reached_state_checked=state_checked) \
.annotate(date_reached_state_construction_ordered=state_construction_ordered)\
.exclude(Q(date_reached_state_checked__isnull=True) & Q(statechange__state=PROJECT_STATE_CHECKED) |
Q(date_reached_state_construction_ordered__isnull=True) & Q(statechange__state=PROJECT_STATE_CONSTRUCTION_ORDERED))
The Project may have no matching StateChange, or one or both.
I need the list to show one Project-line in all cases. My queryset only works for zero or one matching StateChange. It excludes the Projects where both StateChanges are present and I see why it does it when I look at the generated query.
If I do not exclude anything, it shows 1 line for each case.
Can anyone give me a hint about how to make django create the JOINs I need?
We did it by using .extra():
return Projekt.objects.all().extra(
select={
"date_reached_state_checked": "SELECT created_at FROM tracking_statechange WHERE tracking_statechange.projekt_id = projekt_projekt.id AND tracking_statechange.state = 20",
"date_reached_state_construction_ordered": "SELECT created_at FROM tracking_statechange WHERE tracking_statechange.projekt_id = projekt_projekt.id AND tracking_statewechsel.state = 50"
})