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')))
Related
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')
I have a few transformations I need to perform on my table before I aggregate.
I need to multiply transaction_type (which is either 1 or -1) by amount to yield a signed_amount. Then I need to sum all signed_amounts by primary_category (which is a foreign key to secondary category which is a foreign key of my table).
DEBIT = -1
CREDIT = 1
TRANSACTION_TYPE_CHOICES = (
(DEBIT, 'debit'),
(CREDIT, 'credit'),
)
class Transaction(models.Model):
amount = models.DecimalField(max_digits=7, decimal_places=2)
transaction_type = models.IntegerField(choices=TRANSACTION_TYPE_CHOICES)
secondary_category = models.ForeignKey(Secondary_Category)
class Primary_Category(models.Model):
name = models.CharField("Category Name", max_length=30)
category = models.ForeignKey(Primary_Category_Bucket)
class Secondary_Category(models.Model):
name = models.CharField("Category Name", max_length=30)
primary_category = models.ForeignKey(Primary_Category)
I'm stuck on the first bit though.
from django.db.models import Sum, Count, F
original_transactions = Transaction.objects.all()
original_transactions.signed_amount = F('transaction_type') * F('amount')
for transaction in original_transactions:
print transaction.signed_amount
When I try to sanity check that signed_amount is being calculated, I get an error that 'Transaction' object has no attribute 'signed_amount'. I don't want to save signed_amount to the database. I just want to generate it as derived field so I can calculate my totals.
How do I calculate this derived field and subsequently aggregate by primary_category.name?
User python decorator property on a method for class Transaction:
class Transaction(models.Model):
amount = models.DecimalField(max_digits=7, decimal_places=2)
transaction_type = models.IntegerField(choices=TRANSACTION_TYPE_CHOICES)
secondary_category = models.ForeignKey(Secondary_Category)
#property
def signed_amount(self):
return self.amount * self.transaction_type
Then for each Transaction object you can do transaction.signed_amount.
I'm not sure if the aggregation part could be done using queries, but if you don't have that many PrimaryCategory, then python would be good enough to achieve it.
Or you can do this.
all_transactions = Transaction.objects.all().order_by('secondary_category__primary_category_id')
sum = 0
if all_transactions:
primary_category_id = all_transactions[0].secondary_category.primary_category_id
for transaction in all_transactions:
if primary_category_id == transaction.secondary_category.primary_category_id:
sum += (transaction.amount * transaction_type)
else:
sum = (transaction.amount * transaction_type)
print sum
I have a models.py like so:
class ScoreCard(models.Model):
user = models.ForeignKey(User)
course = models.ForeignKey(Course)
created = models.DateTimeField(default=datetime.now)
score = models.IntegerField()
holes = models.IntegerField(
default=9
)
handicap = models.IntegerField(default=0)
class UserProfile(User):
...
def get_nine_stats(self, course):
nine_stats = ScoreCard.objects.filter(course=course) \
.filter(holes=9) \
.aggregate(Avg('score'), Max('score'), Min('score'))
return nine_stats
This is fine and returns almost what I need - a dict of max, min and avg. However, I really want those values with the associated created fields. Is this possible using the aggregate method?
I Have 3 models
class Room(models.Model):
house = models.ForeignKey('Property', related_name='rooms')
beds = models.IntegerField(max_length=10)
class Property(models.Model):
......
def free_places():
places = 0
for r in self.rooms:
x = r.beds - ((r.tenant).size())
places = places + x
return places
class Profile(model.Models):
room = models.ForeignKey(Room, blank=True, null=True, related_name='tenant')
First of all I would like to know if free_places method should be: free_places(self) or free_places(). I think it has some errors too but I don't know how to test it, so here it's the question how can I call the method? and is it correct the function?
I want to call it from a django template.
To try it from "./manage.py shell" what do I need?
Thanks
It should be free_places(self):
You can define the method as a property and then call that from the template:
https://docs.djangoproject.com/en/dev/topics/db/models/#model-methods
Last example in that code block
def _free_places(self):
places = 0
for r in self.rooms:
x = r.beds - ((r.tenant).size())
places = places + x
return places
free_places = property(_free_places)
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)