I have this model:
class Foo(models.Model):
foo_id = models.IntegerField()
foo_old_prize = models.FloatField()
foo_new_prize = models.FloatField()
def get_dif(self):
return self.foo_old_prize - self.foo_new_prize
Is there some trick how to do this Foo.objects.all().order_by('get_dif') ?
Thx
Look into the extra Django queryset operator:
q = Foo.objects.extra(select={'dif': 'foo_old_prize - foo_new_prize'})
q = q.extra(order_by = ['dif'])
You can use extra for this:
Foo.objects.extra(
select={'diff':'foo_old_prize - foo_new_prize'},
order_by=('diff',)
)
I'm not sure you can do it like that.
Here's another method that should work:
objList = Foo.objects.all()
objList.sort(key = get_dif)
Related
I'm beginner and I need some solution
First, I have Racket and Detail class.
class Racket(models.Model):
name = models.CharField(max_length=20)
class RacketDetail(models.Model):
racket = models.OneToOneField(Racket, related_name='detail', on_delete=models.CASCADE)
adminReview = models.TextField()
adminPower = models.FloatField(default=0)
adminSpin = models.FloatField(default=0)
adminManeuverability = models.FloatField(default=0)
adminStability = models.FloatField(default=0)
adminComfort = models.FloatField(default=0)
#property
def adminAvgScore(self):
scoreAvg = (
self.adminPower +
self.adminSpin +
self.adminManeuverability +
self.adminStability +
self.adminComfort
) / 5
return round(scoreAvg, 2)
Second, I want to rander list using the #property(adminAvgScore), so I made view like this.
def racketMain(request: HttpRequest):
getRacket = Racket.objects.all().order_by('detail__adminAvgScore')
return render(request, "racket/racketMain.html", {'racketItems': getRacket, })
Unfortunally when I use 'RacketDetail' class's column I can access all column except 'adminAvgScore' using by "order_by('detail__".
If I use like "order_by('detail__adminAvgScore')" then Django show to me error "Unsupported lookup 'adminAvgScore' for BigAutoField or join on the field not permitted."
How can I solve it? Or should I think in a different way?
You cannot use property with Query as Property is Function. You can use annotate and aggregate combination to get the result as your property function but inside a query.Something like this will do the trick.
from django.db.models import F, Sum, FloatField, Avg
Model.objects.filter(...)\
.values('id')\
.annotate(subtotal=Sum(...math here..., output_field=FloatField()))\
.aggregate(total=Avg(F('subtotal')))
I have a models that has a M2M relationship to another model.
These are my models:
class Catalogue(models.Model):
city = models.CharField(db_index=True,max_length=100, null=True)
district = models.CharField(db_index=True,max_length=100, null=True)
type = models.ManyToManyField(Type, db_index=True)
datetime = models.CharField(db_index=True, max_length=100, null=True)
class Type(models.Model):
name = models.CharField(max_length=100)
def __str__(self):
return self.name
And this is views.py:
class all_ads(generic.ListView):
paginate_by = 12
template_name = 'new_list_view_grid-card.html'
def get_queryset(self):
city_district = self.request.GET.getlist('city_district')
usage = self.request.GET.get('usage')
status = self.request.GET.get('status')
last2week = datetime.datetime.now() - datetime.timedelta(days=14)
status = status.split(',')
if usage:
usage = usage.split(',')
else:
usage = ['1','2','3','4','5','6','7','8','9','10','11','12','13','14','15','16','17','18','19','20','21','22','23','24','25','26','27','28','29','30','31']
intersections = list(set(status).intersection(usage))
type_q = (Q(type__in=intersections) & Q(type__isnull=False))
result = models.Catalogue.objects.filter(
Q(datetime__gte=last2week) &
type_q &
((reduce(operator.or_, (Q(city__contains=x) for x in city_district)) & Q(city__isnull=False)) |
(reduce(operator.or_, (Q(district__contains=x) for x in city_district)) & Q(district__isnull=False)))
).distinct().order_by('-datetime').prefetch_related('type')
return result
I want to filter MySQL db with some queries and return result in a listview.
It works good on a small database, but with large database it takes over 10 seconds to return results. If I delete type_q query, It takes 2 seconds (reduce 10 second!).
How can I improve performance of __in queryset?
It looks like type_q itself is not really the culprit, but acts as a multiplier, since now we make a LEFT OUTER JOIN, and thus the __contains runs over all combinations. This is thus more a peculiarity of two filters that work together
We can omit this with:
cat_ids = list(Catalogue.objects.filter(
Q(*[Q(city__contains=x) for x in city_district], _connector=Q.OR) |
Q(*[Q(district__contains=x) for x in city_district], _connector=Q.OR)
).values_list('pk', flat=True))
result = models.Catalogue.objects.filter(
Q(datetime__gte=last2week),
type_q,
pk__in=cat_ids
).distinct().order_by('-datetime').prefetch_related('type')
Some database (MySQL is known to not optimize a subquery very well), can even do that with a subquery with. So here we do not materialize the list, but let Django work with a subquery:
cat_ids = Catalogue.objects.filter(
Q(*[Q(city__contains=x) for x in city_district], _connector=Q.OR) |
Q(*[Q(district__contains=x) for x in city_district], _connector=Q.OR)
).values_list('pk', flat=True)
result = models.Catalogue.objects.filter(
Q(datetime__gte=last2week),
type_q,
pk__in=cat_ids
).distinct().order_by('-datetime').prefetch_related('type')
Let's say that i have this queryset :
result_list = []
get_result_list = [x for x in search_text_imported.split() if len(x) > 2]
for keyword in get_result_list:
result_list += list(Node.objects.filter((Q(name__icontains=keyword) | Q(Tags__icontains=keyword)), tree_type='root', tunisia_office=True, published=True ).order_by('-bookmarked_by'))
result = list(OrderedDict.fromkeys(result_list))
models.py
class Node(MPTTModel):
name = models.TextField(blank=True, null=True)
bookmarked_by = models.ManyToManyField(CustomUser, null=True, blank=True)
I want to show first the objects that have the most number of entries in the bookmarked_by field.
Is there a way to do it ?
Any help is appreciated.
Use the aggregate function Count
from django.db.models import Count
Node.objects.annotate(
num_bookmarks=Count('bookmarked_by')
).order_by('-num_bookmarks')
https://docs.djangoproject.com/en/2.2/topics/db/aggregation/#aggregation
I have 2 classes in model
class A(models.Model):
name = models.CharField(max_length = 20)
class B(models.Model):
a = models.ForeignKey(A)
and I want to filter objects of B which does not have 'a' not has name of "exclude".
I tried
objects = B.objects.exclude(a.name == "exclude")
in my view, but it does not work.
How can I do this?
This will work:
objects = B.objects.exclude(a__name="exclude")
objects = B.objects.exclude(a__name="exclude")
or
from django.db.models import Q
objects = B.objects.filter(~Q(a__name="exclude"))
but the former one is good enough..
I have the following model structure below:
class Master(models.Model):
name = models.CharField(max_length=50)
mounting_height = models.DecimalField(max_digits=10,decimal_places=2)
class MLog(models.Model):
date = models.DateField(db_index=True)
time = models.TimeField(db_index=True)
sensor_reading = models.IntegerField()
m_master = models.ForeignKey(Master)
The goal is to produce a queryset that returns all the fields from MLog plus a calculated field (item_height) based on the related data in Master
using Django's raw sql:
querySet = MLog.objects.raw('''
SELECT a.id,
date,
time,
sensor_reading,
mounting_height,
(sensor_reading - mounting_height) as item_height
FROM db_mlog a JOIN db_master b
ON a.m_master_id = b.id
''')
How do I code this using Django's ORM?
I can think of two ways to go about this without relying on raw(). The first is pretty much the same as what #tylerl suggested. Something like this:
class Master(models.Model):
name = models.CharField(max_length=50)
mounting_height = models.DecimalField(max_digits=10,decimal_places=2)
class MLog(models.Model):
date = models.DateField(db_index=True)
time = models.TimeField(db_index=True)
sensor_reading = models.IntegerField()
m_master = models.ForeignKey(Master)
def _get_item_height(self):
return self.sensor_reading - self.m_master.mounting_height
item_height = property(_get_item_height)
In this case I am defining a custom (derived) property for MLog called item_height. This property is calculated as the difference of the sensor_reading of an instance and the mounting_height of its related master instance. More on property here.
You can then do something like this:
In [4]: q = MLog.objects.all()
In [5]: q[0]
Out[5]: <MLog: 2010-09-11 8>
In [6]: q[0].item_height
Out[6]: Decimal('-2.00')
The second way to do this is to use the extra() method and have the database do the calculation for you.
In [14]: q = MLog.objects.select_related().extra(select =
{'item_height': 'sensor_reading - mounting_height'})
In [16]: q[0]
Out[16]: <MLog: 2010-09-11 8>
In [17]: q[0].item_height
Out[17]: Decimal('-2.00')
You'll note the use of select_related(). Without this the Master table will not be joined with the query and you will get an error.
I always do the calculations in the app rather than in the DB.
class Thing(models.Model):
foo = models.IntegerField()
bar = models.IntegerField()
#Property
def diff():
def fget(self):
return self.foo - self.bar
def fset(self,value):
self.bar = self.foo - value
Then you can manipulate it just as you would any other field, and it does whatever you defined with the underlying data. For example:
obj = Thing.objects.all()[0]
print(obj.diff) # prints .foo - .bar
obj.diff = 4 # sets .bar to .foo - 4
Property, by the way, is just a standard property decorator, in this case coded as follows (I don't remember where it came from):
def Property(function):
keys = 'fget', 'fset', 'fdel'
func_locals = {'doc':function.__doc__}
def probeFunc(frame, event, arg):
if event == 'return':
locals = frame.f_locals
func_locals.update(dict((k,locals.get(k)) for k in keys))
sys.settrace(None)
return probeFunc
sys.settrace(probeFunc)
function()
return property(**func_locals)