Is it possible to modify prefetched objects without using save()?
class First(models.Model):
field = models.IntegerField()
class Second(models.Model):
first = models.ForeignKey(First, related_name='seconds')
some = models.IntegerField()
qs = First.objects.filter(field=12).prefetch_related('seconds')
qs[0].seconds.all()[0].some = 999
qs[0].seconds.all()[0] == 999 # should be True
UPDATE:
I found what was wrong. First need evaluate queryset e.g. len(qs) after filter.
I want to alter my question slightly. Can i modify foreign key relationship without hitting db?
qs = First.objects.filter(field=12).prefetch_related('seconds')
len(qs)
print(len(qs[0].seconds.all())) # output: 5
qs[0].seconds.all()[0].first_id = 2
print(len(qs[0].seconds.all())) # output: 4
Instead of doing
f.seconds.all()[0].some = 999
f.seconds.all()[0] == 999 # should be True
Do this..
first_object = f.seconds.all()[0]
first_object.some = 999
first_object.some == 999 #true
Related
if i inserting the number 5 i want to check all the numbers before 5( like 1,2,3 and 4 )is must have inside the db ,then only can i add the number 5 ,otherwise show error. And also check is any duplication in the Db using rest django model serilaizer.
def validate_match_round(self, match_round):
if not match_round :
raise serializers.ValidationError("Enter value more than 0 ")
matchscore model
class Matchscore(TimeStampedModel):
gameevent = models.ForeignKey(GameEvent, null=True, related_name='game_event',on_delete=models.DO_NOTHING)
match_round = models.IntegerField(null=True,blank=True)
team_a = models.ForeignKey(Team,null=True,related_name='team_one',on_delete=models.DO_NOTHING)
team_a_score = models.PositiveIntegerField(null=True,blank=True)
team_b = models.ForeignKey(Team,null=True,related_name='team_two',on_delete=models.DO_NOTHING)
team_b_score = models.PositiveIntegerField(null=True,blank=True)
team_won = models.ForeignKey(Team,null=True,related_name='team', on_delete=models.DO_NOTHING)
if match_round == 1:
return match_round
match = Matchscore.objects.aggregate(Max('match_round'))
print(match)
if match_round == match["match_round__max"] + 1 :
return match_round
else:
raise serializers.ValidationError("Enter a valid match_round")
all_rounds = Matchscore.objects.filter(match_round__lte=match_round).order_by('match_round').values_list('match_round', flat=True)
Will return list of match_round values that lower or equal than match_round passed to function
all_rounds_count = Matchscore.objects.filter(match_round__lte=match_round).count()
Will return count of these rounds. and if (all_rounds_count + 1) == match_round check is what you want
And also check is any duplication in the Db using rest django model serilaizer.
To avoid keys duplication
Set unique=True for model.Field to disable round duplicates match_round = models.IntegerField(..., unique = True)
Add unique validator to serializer
I have a Item model with a numeric number field. This number field defaults to null.
# models.py
class Item(models.Model):
number = models.IntegerField(default=None, blank=True, null=True)
I want to set-up filters that can return a queryset of Items where number is in range - which is straightforward enough:
# filters.py
class ItemFilter(django_filters.FilterSet):
min_num = django_filters.NumberFilter(method="min_num_filter")
max_num = django_filters.NumberFilter(method="max_num_filter")
class Meta:
model = Item
fields = ("min_num", "max_num", "incl_null")
def min_num_filter(self, queryset, name, value):
return queryset.filter(number__gte=value)
def max_num_filter(self, queryset, name, value):
return queryset.filter(number__lte=value)
But what if I want to have an additional Boolean filter that can include Items that has null for number along with whatever Items matches the min_num and max_num range?
So for example, a URL query in the form of ?min_num=1&max_num=10&incl_null=True should return all Items where number is between 1 and 10 OR number is equal to None.
The following code does not work:
class ItemFilter(django_filters.FilterSet):
...
incl_null = django_filters.BooleanFilter(method="incl_null_filter")
class Meta:
model = Item
fields = ("min_num", "max_num", "incl_null")
// doesn't work
class incl_null_filter(self, queryset, name, value):
if value is True:
return queryset | Item.objects.filter(number=None)
if value is False:
return queryset
Edit: I've tried the methods in the "Filtering by empty values" documentation but I think that's for null values exclusively - where I'm looking for a range match OR a null value.
Try this query:
from django.db.models import Q
min_ = 0
max_ = 10
Item.objects.filter(Q(number__gte=min_, number__lte=max_) | Q(number__isnull=True))
Well, the only solution I can think of is to pass the min range, max range, and is_null boolean into a single char field then convert it into the 3 individual filters for actioning.
So the query URL will look like ?master_num=1-10-1 for range 1 - 10 incl. None and ?master_num=1-10-0 for range 1 - 10 excl. None.
class ItemFilter(django_filters.FilterSet):
master_num = django_filters.CharFilter(method="master_num_filter")
class Meta:
model = Item
fields = ("master_num")
def master_num_filter(self, queryset, name, value):
# array = [min, max, 1 or 0 for True and False]
array = value.split("-")
min = Q(year_published__gte=int(array[0]))
max = Q(year_published__lte=int(array[1]))
if array[2] == "1":
incl_null = Q(year_published=None)
return queryset.filter((min & max) | incl_null)
else:
return queryset.filter(min & max)
Would like to know if there's a better way to do this.
I have two tables as follows,
cabinet
cabinet_id cabinet_name
1 Test1
2 Test2
3 Test3
cabinet_maping
id product_id cabinet_id size
1 34 1 20
2 34 3 25
How can I select all cabinet_name from cabinet table where cabinet_maping.product_id = 34 in Django
Expected Output as follows,
cabinet_id cabinet_name size
1 Test1 20
2 Test2 0
3 Test3 25
I think that yours models could look like
class Cabinet(models.Model):
name = models.CharField(max_length = 30)
class cabinet_maping(models.Model):
product = models.ForeignKey(Product)
cabinet = models.ForeignKey(Cabinet)
size = .....
You should do sth like this:
cabinet_name = cabinet_maping.objects.filter(product__id = 34)
for item in cabinet_name:
print item.cabinet.id
print item.cabinet.name
print item.size
I didn't check it but i think that should work (that works :))
I agree with Silwestpl that your models are wrong as using Foreign Key would make this query a lot easier. But just an answer to your question would be. I am assuming that you dont have any relationships between the two tables as you haven't mentioned any.
x = Cabinet_mapping.objects.filter(product_id = somevalue).distinct('cabinet_id')
response_list = []
for y in x:
response_dict = {}
response_dict['cabinet_id'] = y.cabinet_id
response_dict['cabinet_name'] = cabinet.objects.get(id = y.cabinet_id).cabinet_name
response_dict['size'] = y.size
response_list.append(response_dict)
return response_list
This would be the answer according to the details you have provided.
But Ideally I would do something like this
class Product(models.Model):
# id is generated automatically.
## any other fields that you want for product.
class Cabinet(models.Model):
# again id is auto-genearated.
cabinet_name = models.CharField(max_length=100)
cabinet_size = models.IntegerField()
products = models.ManytoManyField(Product)#This automatically maps product_id n cabinet_id.
And your query would be.
x = Cabinet.objects.filter(product.id=some_value)
print (x.id , x.cabinet_name, x.cabinet_size) # I used print, but you can use it anyway you want.
This would be what you require. Please use the second solution if you are looking into something serious.
I have 3 models in django:
class Movie(models.Model):
mid = models.IntegerField(primary_key = True)
name = models.CharField(max_length = 100)
class User(models.Model):
username = models.CharField(max_length=128, null=True)
uid = models.CharField(max_length=100)
movie = models.ManyToManyField(Movie, through = "Vote")
class Vote(models.Model):
movie = models.ForeignKey(Movie)
user = models.ForeignKey(User)
rating = models.IntegerField()
here rating = 0/1, 0 means dislike, 1 means like
i want to make some queries using filters:
find out all movies that a current user likes. For that i use this following 2 queries, but none of them work. In both cases it gives erroneous results
ans = Movie.objects.filter(vote__user = self).filter(vote__rating = 1)
ans = Movie.objects.filter(user__uid = self.uid).filter(vote__rating = 1)
I have a list of users in an array ids. I want to find out how many users from this list like a particular movie?
i tried this, but this is also incorrect:
ret = User.objects.filter(uid__in = ids).filter(vote__movie = mov).filter(vote__rating = 1)
can somebody please help me with these 2 queries?
I'd also suggest letting django assign the model's id's but if you are using a legacy database or for some other reason need to assign the id's you can query like so:
# uid is some uid
user = User.objects.get(uid=uid)
likes = Movie.objects.filter(vote__user=user, vote__rating=1)
or
likes = Movie.objects.filter(vote__user__uid=some_uid, vote__rating=1)
count of people in the list of users who like a specific movie:
>>> uids = ['1','2','3']
>>> # if mov is a Movie instance
>>> votes = Vote.objects.filter(user__uid__in=uids, movie=mov, rating=1)
>>> print votes.query
SELECT "so1_vote"."id", "so1_vote"."movie_id", "so1_vote"."user_id", "so1_vote"."rating" FROM "so1_vote" INNER JOIN "so1_user" ON ("so1_vote"."user_id" = "so1_user"."id") WHERE ("so1_user"."uid" IN (1, 2, 3) AND "so1_vote"."movie_id" = 1 AND "so1_vote"."rating" = 1 )
>>> # if mov is a mid for a movie
>>> # get movie instance by using Movie.objects.get(mid=mov)
>>> # or query:
>>> # votes = Vote.objects.filter(user__uid__in=uids, movie__mid=mov, rating=1)
>>> likes_count = votes.count()
>>> print likes_count
0
combined:
likes_count = Votes.objects.filter(user__uid__in=uids, movie=mov, rating=1).count()
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)